JOES Chassis Sheets are formatted for you to download and make as many copies as you want on your personal printer or copy machine. Tell your racing friends and spread the word about the JOES Free Download!
- JOES Chassis Sheets PDF
Roll Center Magic
Dialing in your Front Roll Center could be the magic difference that makes your car prevail in the center of the turn. But, is it really magic? I think that many times we over analyze Roll Center when really it is just another adjustment. We throw springs at the car and make shock changes. We adjust the bite and stagger on a whim. Changing the Front Roll Center at the track is crazy talk – or is it?
For perspective – we often move the Rear Roll...read more »
Using and A-Plate slug to adjust your A-Arm inner pivot points gives you an easy and repeatable way to adjust your Front Roll Center right at the track.
You can move the lower points too, but you bring in rack location issues and bump steer corrections. If you take the time in your shop and know which rack spacers and lower pivot slugs to use at the track you could bolt in the new slugs quickly giving you more options. Your options need to consider camber change curves, static settings and bump steer effects. Changing the lower angles relieve you of camber curve considerations but are more time consuming so a focus on the upper A-Arms may be the best trackside compromise?
A slotted A-Arm plate allows you to use slugs to make Front Roll Center Adjustments at the track giving you another weapon in your adjustment arsenal.
Lowering the RF A-Arm inner pivot raises the Front Roll Center and moves it to the right. Negative Camber is added and may need to be reset.
Raising the RF A-Arm inner pivot lowers the Front Roll Center and moves it to the left. Negative camber is reduced and may need to be reset.
Lowering the LF A-Arm inner pivot raises the Front Roll Center and moves it to the left. Positive camber is reduced and may need to be reset.
Raising the LF A-Arm inner pivot lowers the Front Roll Center and moves it to the right. Positive camber is added and may need to be reset.
Adjustable Ball Joints
An adjustable ball joint uses shims to change the A-Arm angle for quick Front Roll Center adjustments right at the track. A-Arm height an angle adjustments can be made just at the ball joint or in conjunction with inner pivot slug adjustments.
To further illustrate the point, I think that Front Roll Center is a design parameter that involves plenty of engineering and thought. I also think that if you have a basic understanding of Roll Center geometry that you can short cut the thought process at the track and simply focus on the LF and RF Instant Centers. At the track – you can easily visualize the effect on the RF instant center if you raise the RF a-arm inner pivot Â½”. At this point in time you car is already “engineered” and you can just make the adjustment. By focusing on the Instant Centers you can readily make repeatable adjustments without having to worry about a bunch of imaginary lines. You can understand Instant Centers and their location quickly and easily. The reality is that Front Roll Center is simply a derivative of the Instant Center locations. Instant Centers are simple even through dynamic roll. Why complicate your trackside thought process with imaginary lines? Save the heavy thinking for the engineering room. At the track - just give it a try!
By understanding the Front Roll Center parameters and the imaginary points you can simplify the process and easily document which slug you are using to adjust your a-arms up and down. Focusing on Instant Centers makes it possible at the track. With this simplified thought process you can add another weapon to your adjustment arsenal and make adjustments that gets you ahead of your competition.
- JOES Farrell Frameworks Complete Rear Axle Diagram 25829-Instructions.pdf
- Build your own axle spacing diagram Build-your-own-axle-spacing.pdf
- Axle spacing reference for Wilwood GP320 caliper with 3/16" rotor Wilwood-GP320-JOES-Rotor.pdf
- Axle spacing reference for Wilwood GP320 caliper with 1/4" rotor Wilwood-GP320-250-Rotor.pdf
- Axle spacing reference for Wilwood Dynapro Single caliper with 3/16" rotor (JOES single bearing caliper carrier P/N 25786) Wilwood-Dynapro-25786-JOES-Rotor.pdf
- Axle spacing reference for Wilwood Dynapro Single caliper with 3/16" rotor (JOES double bearing caliper carrier P/N 25788) Wilwood-Dynapro-JOES-Rotor.pdf
JOES Setup Sheets are formatted for you to download and make as many copies as you want on your personal printer or copy machine. Tell your racing friends and spread the word about the JOES Free Download!
- Micro Sprint Setup Sheets
Setting the bar
Evolution in racing has created new set up options. Installing and adjusting your sway bar correctly will help you to achieve repeatable speed. Whether you run a standard 1 1/8” bar or a 2” big bar you team should have a reproducible routine to ensure the bar is loaded as anticipated every time.
Establishing a Baseline
Whether you use a standard one-piece bar or a three-piece big bar, your sway bar will work more efficiently if you mount the link that connects to the lower control arm at 90 degrees.
Upon arrival at the track and with your car race ready it really pays to set up your scales on the most level ground you can find. Shim the scale pads if needed and mark the pad location so that you can weigh the car at the track in the same spot. Once the scales are set up, weigh the car and record any difference that might be created due the track ground not being level as compared to your shop set up. By establishing a baseline at the track, you will be able to make adjustments and use your baseline to maintain proper loading of the bar, ride heights and wedge. An established baseline will help to get you back to your desired numbers even after many trackside changes. Check the sway bar at the track, with the car on the scales, and note any difference in preload as compared to when you set the bar in the shop.
With a standard 1-1/8” bar and your car in race ready condition I recommend setting the sway bar on perfectly level ground. Race ready means that the next thing your car does is head right on the track. Full of fuel and everything set. Your shop should have marked places on the floor so that the car is weighed in the same level place each time. Spend the time to make the scale pads are perfectly level in your shop.
Setting the bar on the scales allows you to verify that the wedge is set to the desired number every time. With a standard set up and 1-1/8” bar setting the bar with the driver in the car works best. When the driver is in the car you make your adjustments accounting for the 12 pack of beer and large pizza your driver consumed during the week. Set your ride heights, stagger, air pressure, front to rear balance, and wedge. Be sure the fuel tank is full. If you run high rebound adjustable shocks make sure to open them up for the set up routine or have a set of dummy shocks of the same brand that are used only in the shop for set up purposes.
Personally, with a 1-1/8th inch bar I recommend loading the bar Â½%. Many teams choose to run the bar neutral which is just fine. I always felt that the Â½% preload helped the driver get into the corner. If your driver is smooth, and your corner transitions are modest, then neutral can help keep the care free in the middle. You can create your own preload setting and adjust as needed at the track but having a routine is the goal.
With a big-bar Mike Leary of Leary Racing Shocks recommends adding wedge to the car by preloading the bar. Leary sets the wedge in the springs and then adds additional wedge with 3-6 turns of preload and sometimes has winning success using 9 turns. There is some debate here as some chassis experts think big bars are too sensitive and they prefer to run them neutral - Chuck Carruthers is in this camp.
With a big 2” bar there is debate on how to establish a set up routine. I see teams that have their crew jump on the front bumper to get it down to the stops where they then set the bar. This may work for some teams but I think there are too many variables for this procedure to be consistent. Even with a big bar set up, I recommend setting the bar at ride height. Mike Leary of Leary Racing Shocks likes to use the big bar to add wedge to the car. Mike recommends setting minimal wedge in the springs and then adding 2 to 4 percent of additional wedge in the bar to reach your desired wedge total.
If you are running a bump stop set up west coast set up guru Chuck Carruthers recommends pulling the springs and letting the car sit down on the stops. Chuck then sets the bar neutral with the car on the stops and with the driver in the car.
The one time it might make sense to have your crew stand on the bumper is when you are running a LF coil bind set up. Setting the bar with the coils bottomed out provides for fixed compression against a solid surface. If you run coil bind in the front, Carruthers recommends loading the bar 3-5 turns once the coils have reached the bind point. Coil bind set ups are really reserved for teams that can afford testing to work out all the bugs.
Using a frame rail slider system to mount the sway bar allows you to move the sliders for perfect sway bar alignment with the lower control arms reducing binding and increasing consistency.
Mounting your sway bar properly is very important. Ensuring that attachment points run 90 degrees and are free from binds helps to keep your car fast. Awkward angles can create binding through travel making car performance unpredictable.
Utilizing bushings to support the sway bar in the bar eyes is a vast improvement over letting the bar grind against old style steel sway bar eyes. Installing slider sway bar mounts on both frame rails allows you to adjust the bar location so that your bar stays lined up even if you switch to different length arms giving you more adjustability in your car. Some sway bar arms have multiple holes to connect to the lower control arm. Shortening the sway bar arm increases the effective bar rate and with the slider bar mounts you can move the entire bar to keep the links 90 degrees for optimal performance.
Using sway bar eye bushings keeps your bar running smoothly and eliminates binding. A swivel eye self adjusts for perfect alignment. This swivel eye is removable allowing the bar to be dropped out the bottom for quick sway bar changes.
Swivel adjustment eyes allow you to use a ratchet to load the bar making for quick and easy adjustments. The swivel system allows you to preload the biggest bars with ease. The swivels prevent binding and self adjust keeping in line with the bar. Quick sway bar changes can be made as the swivel eye unbolts allowing the bar to be dropped out the bottom.
Adding preload to a sway bar effectively increases its rate. If your team feels you need a bigger bar you can wind in some load to see if you are going in the right direction before spending the time to change out the entire bar. Moving the sway bar links just one hole has a profound effect and is another adjustment option.
If your car is a little loose on entry then adding preload to the bar can help to settle it on entry. A bar that is neutral or set slack can, at times, cause a loose entry condition. A quick preload adjustment can be made during practice and your driver can give you an instant report. My feeling is that race teams should do everything in their power to avoid a car that is loose on entry. If your car is tight in the middle the driver can compensate with a different line to help minimize the push. With a loose entry condition the only thing the driver can do is to slow down. Loose entry should be avoided at all costs and in this condition winding turns in your sway bar may be good fix.
Choosing the right bar is difficult. The best way is to consult with your chassis builder and simply watch what your competition is doing. At many tracks it remains to be seen if the new big bar concept is better than the traditional bar set up. Most crew chiefs agree that the big bar set up is good when you hit it. The offsetting factor is that the big bar concept is finicky and you can be out to lunch as soon as the smallest variable is introduced. For less experienced drivers a standard bar set up is going to produce more feel helping them through their learning curve.
Whether you use a standard bar or a big bar establish a routine so that your sway bar is set the same way each and every time. When you preload a sway bar the increase in rate is exponential as you add turns of load. Teams should experiment with the car on the scales and record the wedge number increase with each turn. Charting the wedge change with each turn of preload only takes a few minutes and it will give teams the information they need to make precision changes at the track.
The bottom line is that a smooth operating sway bar that is installed free of binds will make your car faster. The precision parts available today offer an advantage. In the past, one piece sway bars were simply bolted in and taken for granted. Your team can find consistency and extra speed by tuning up your sway bar installation coupled with a sound routine for loading the bar.
Camber and the Tire Contact Patch
Drivers like cars that cut into the turn. Optimizing your camber and understanding the tire contact patch will make for a faster car that stays fast through out the race. With today’s highly engineered tires, bump stop set ups and high level competition adjusting camber for maximum grip will help you win.
Camber is simply the tilt of the tire. Standing in front of the car if the top of either of the tires tilts towards the engine it...read more »
A billet caster camber gauge
A billet caster camber gauge has the machined surfaces for accurate readings.
Camber is essential to match the contact patch to the bank of the turn balanced against your Upper A-Arm and Lower Control Arm lengths. Even if the corner were flat we would want camber. We need camber to work with the Upper and Lower Control Arms to achieve proper camber gain through suspension travel. Camber coupled with gain will optimize the tire contact patch taking advantage of the tire construction parameters.
Tire Contact Patch Explained
For this tire contact patch exercise think of a trampoline – we are going to compare a trampoline to how a race tire works. Imagine a trampoline to create a mental illustration of how the tire contact patch is stretched. Think of the trampoline outer frame as the tire bead. Now think of the tire side wall as the trampoline springs. Compare the trampoline surface to the tire rubber contact patch and visualize how tightly and evenly the trampoline surface is stretched by springs towards the frame. Our goal is to have the tire contact patch stretch evenly and tightly just like the trampoline surface. The tire bead is very rigid and creates a sturdy frame. The side wall of the tire is a spring that absorbs loads. By using camber to maximize the power of the sidewall springs the contact patch stretches flat and stays in full contact with the ground producing more grip.
The ideal amount of camber is achieved when the inside sidewall sets into the track to provide maximum pull at the tire contact surface. The stretch pulls evenly from the inside sidewall to the outside sidewall. The correct camber setting will utilize the entire contact patch. If you have too much camber the inside of the tire will not have enough initial surface area to pull the contact patch across and the spring of the outer sidewall will not be engaged. Not enough camber and the contact patch will deform and ball up at the inside edge – the contact patch rolls up and off the ground as the inner side wall spring needs more loading.
We use pyrometers to measure the tires on the inside, middle and outside. When the pyrometer shows a hot temp on the outside of the RF we add camber. Too hot on the inside RF and we take camber out. There is an exception that goes against the common thought of taking out camber when the pyrometer shows a hot reading on the inside. When would you add camber even though it opposes the pyrometer readings? Understanding the tire contact patch will help you set the camber through the exception.
With your trampoline comparison at the front of mind visualize the RF tire surface as it rolls through the turn. Think about the part of the turn where cars choose to cut or push. At this full tire load point, if you do not have enough camber, the contact foot print will not be stretched tightly between the two sidewalls (like in our trampoline comparison) and the pyrometer will show excessive heating on the inside of the tire and the exception occurs. In this condition we add camber even with higher inside RF temps. The excessive heating on the inside generally indicates to take camber out – thinking outside of the numbers may be in opposition to typical camber adjustments.
Understanding the Contact Patch
This exagerated view of a contact patch buldge illustrates how too little camber can show a hot reading on the inside. Understanding the contact patch will help you to make the right adjustment.
You may indeed need to take out camber of the RF due to the excessive inside readings but before you do inspect the tire and look for the exception. Look for rolling at the outside edge. If you see scuff marks extending to the outside sidewall this is clue one. If the outside edge looks rounded this is clue two. Now the important clue – closely inspect the inside of the RF tire about 1” inch from the inside edge. Look for a strange wear area that is about Â½” wide that looks different than the surrounding rubber. It will look grainy, be cupped or perhaps mimic wind blown sand on the desert. Remember – it is more effective to dial in camber with new tires. Worn tires may have been misused and can provide false readings. Added attention should be paid to tire temps when you bolt on a new set and high quality pyrometers should always be used. Tire Temps make the most sense when the car is close. Feedback from temps can be erratic if the car is way off.
If you do not have enough RF camber inside sidewall will be under loaded. The outside sidewall gives way and folds in deforming the contact patch. The deformed tire footprint pulls up off the track surface – as the deformed contact patch reaches the inner sidewall it is forced back down creating a protruding bulge as it curves back to the inner sidewall. Remember the trampoline comparison, we need the contact patch stretched evenly from the sturdy outside bead, through the outside sidewall spring, tightly across the contact patch, through the inner sidewall to the firm inner bead. In this exception adding camber at the RF will load the inside tire wall with the ability to firmly hold the inner edge of the tire foot print. The rolling or protruding of rubber at the inside edge is due to inadequate static RF camber. Don’t be fooled by this short term and artificial temperature. The extra temperature is created from the deformed contact patch bulge as it curves back to the inner sidewall. The bulge rubber will quickly grind off permanently damaging the tire. and the true pyrometer reading will show up! Proper camber will give the inside of the tire the maximum grip allowing the contact patch to stretch trampoline tight all the way across. Proper camber will allow the outside side wall to be pulled in by the contact patch rubber connecting the inner and outer sidewalls in unison and with equal load.
Camber - Old School
Camber gain through travel is related to your static camber, your Upper A-Arm and Lower Control Arm lengths. Consider the amount of travel your front end experiences. If you have an old school set up verses a Bump Stop Set Up there is less overall travel and the Upper A-Arm will be short. With Bump Stop Set Ups there is more travel from your static ride height and much longer Upper A-Arms slow camber gain.
For a pavement touring late model old school thinking was about 1 degree of camber gain per inch of travel. This guideline was a rough starting point with traditional set up and would be adjusted as needed to actual conditions. With a 17 Â¾” RF Lower Control Arm a typical Upper A-Arm would range from 7 to 8.5” +/-. The increased angle of the Upper A-Arm provided for camber gain from static to maximum load. With standard suspension travel and a static camber of 3.5 degrees negative you would achieve about 5 to 6 degrees of camber in the center of the turn. Gain would be 1.5 to 2.5 degrees of camber through travel. Every car and track is different and these ball parks give are a simple view of old school camber
Camber - Bump Stop Set Ups
Bump Stop Set Ups require Upper A-Arms to be considered in an entirely different way. Longer Upper A-Arms slow down camber gain so it is wise to measure your camber with the car on the bump stops emulating the center of the turn. Static ride height is of zero value on a Bump Stop Set Up – as soon as you reach race speed the car is down on the stops and never sees static height again until you load it back in the trailer. Since shocks with mammoth amounts of rebound hold the car down on the bump stops the ride height static camber is not even worth checking. Bump Stop Set Ups use much longer Upper A-Arms, such as 8” to 12”, yet the Lower RF Control Arm is still around 17 Â¾ on a touring late model.
When using bump stops be sure to consider your A -arm lengths and angles.
Your goal in identifying the proper camber is to find the optimal camber amount that creates maximum tension across the tire surface by equally loading the inner and outer sidewall. Dialing in the camber for the conditions will help the car turn. Too much RF camber and the inside edge will not hold – not enough and you will get balling up at the inside edge.
To set camber with your Bump Stop Set Up I would pick a repeatable ride height down on the stops that represents your best estimation of ride height in the center of the turn. A repeatable middle of the corner ride height number will make a better week to week reference point then trying to chase a ride height that varies based on how you adjust the shock body etc. For a Bump Stop Set Up I would start with 4.5 degrees of negative camber at the RF at my mid corner reference point and would not even care about static ride height camber. I would dial in the optimal camber with my pyrometer and tire inspections. I would look for consistent tire temps on short runs with new tires and longer runs with the same new tires. Adding or subtracting from my initial set up would be based on the feedback the car provides. The left front starting setting would be 3 degrees positive with the car on the stops and I would experiment there.
Tire Temp Tip
From experience my fastest cars had RF inside temps that were 10 to 14 degrees hotter than outside temps. The small amount of extra inside heat ensured that I was just reaching over the edge giving me the best shot at a fully stretched contact patch. I made sure to verify the temps on both short and long runs with new tires. The LF has less load so 12 to 16 degrees hot on the outside temp showed me LF outside tire wall was digging in with everything it had.
Three Link Lessons
Have you ever driven a forklift or other hot rod that had the steer wheel in the back instead of the front? Rear steer rigs turn quickly and the term “push” just would never apply. Understanding your three link suspension can give you adjustment tools to help you roll through the center of the turn or help to hook you up on exit.
In general your static rear setting should be dead square. In your shop you need to spend the time needed to ensure...read more »
To really add over steer at the rear end housing you can mount the front pivot point of the RR trailing arm towards the center of the car. With the trailing arms toed in at the front you can use the J-Bar mounting angle to help steer the rear end through roll. If you run the frame side of the J-bar is higher than the pinion side the rear end housing moves left through roll. As the housing moves left the RR trailing arm gets longer and pushes the RR tire back producing rear steer that will help the car turn.
If you want the rear end housing to under steer then mounting the RR trailing arm level and perpendicular to the rear end housing will produce the desired result. As the car rolls the RR Trailing are will shorten pulling the RR tire ahead.
When it comes to trailing arms I try to avoid linkage arrangements that go though center under roll. In other words – if the trailing arm starts on an uphill angle I do not want it to go past level and then head downhill. If the travel was enough to create a down hill angle under full roll I would make an adjustment as this can make the care unstable. I want to avoid having the RR tire to move back and avoid having the trailing arm travel through level which would cause the RR to begin moving forward.
Typically, I like run the LR trailing arm up hill about Â¾” to 1”. There is much debate on this but I like to have a little anti-squat in the car to promote bite under acceleration. If you run a high amount of wedge then level may be a better idea. Since the left side is lifting in the corner the angle increases and the LR trailing arm shortens and keeps moving in the same direction. Again, when it comes to trailing arms I try to avoid linkage arrangements that go though center under roll as going through center can create an unstable car.
Mounting the LR trailing arm with the inner pivots towards the center of the car coupled with the J-Bar running downhill from the pinion to the frame will pull move the LR tire back during roll promoting under steer.
By thinking out the trailing arm angles in conjunction with the J-Bar angle you can guide the rear end housing on the path that helps your set up through the turn. Running the J-Bar higher on the frame side will push the rear end housing to the left through roll. If you run the frame side lower or level the rear end housing will move right through roll. Using the J-Bar mounting angle to in conjunction with trailing arm angles both up and down and left to right gives you another tool in your arsenal helping you to achieve faster lap times.
Slotted Pinion Mount
A slotted pinion mount allows you to quickly set the J-Bar angle. Running the J-Bar higher on the frame side as compared to the pinion side moves the rear end to the left through chassis roll. Understanding how the rear end moves gives you adjustment options to dial in your set up for added speed.
Using trailing arm brackets with multiple trailing are mounting holes gives you additional adjustment options. The clamp type aluminum brackets allow you to mount the trailing arm left to right mounting location where ever you want. You can fine tune the trailing arm location and trailing arm toe settings by using spacers to set the left/right angle to meet your needs.
Clamp On Aluminum Trailing Arm Brackets
Clamp on aluminum trailing arm brackets allow you to set the trailing arm angles to help your car turn through the center. You can arrange your three link set up for over steer or under steer through chassis roll. Experienced crew chiefs use the three link set up as part of their set up package.
I recommend running the top link with a fair amount of anti-squat built into the adjustment and a downhill angle of around 4 to 7 degrees. If you run a track where the car is tough to hook up you can get some added bite to the LR under acceleration if you mount the top link closer to the LR wheel. If a track you run is consistently tight then mounting the top link closer to the RR will free the car up under acceleration.
Top Link Mount
A top link mount that is slotted will allow for ultimate fine tuning of your top link anti-squat settings. Top link mounts with multiple holes also work well. Adjusting the anti-squat for your car, driver and track can maximize exit grip getting your team to the finish line first.
Top link mounting ears with multiple holes or slots will give you more room for adjustability. You can choose mounting ears that have the adjustment holes offset behind the center line of the rear end housing which will add more anti-squat under acceleration. Keep in mind that anti-squat only takes advantage of the available grip through the use of mechanical leverage. Excessive amounts can cause a loose in condition or wheel hop. Occasionally the driver might report that the front wheels feel light under acceleration at the late apex point – if so you should dial back the top link angle and anti-squat for driver feel.
As a general guideline – more anti-squat in your three link suspension works best if you run low amounts of wedge. As wedge numbers increase then you should consider lower amounts of anti-squat. Again, you can make adjustments based on your set up. I prefer low amounts of wedge in an asphalt late model and most of the races that landed my teams in victory lane had 49% to 53% of diagonal. Based on those lower wedge settings I would run a fair amount of anti-squat. Typically, I would run the LR trailing arm up an inch on the front. By using the trailing arm with plenty of angle I could reduce the angle in the top link creating a more stable entry while maintaining the anti-squat I desired. If you run 60% diagonal then running the top link and trailing arm closer to level is a good starting point.
Using your three link suspension to dial in your car is a viable adjustment option that can be performed quickly right at the track. The teams that experiment with the proper three link set up can find the set up that launches their car off the corner with more acceleration to get to the checker first.
Panhard Bar & J-Bar
Adjusting the Panhard Bar or J-Bar always generates feedback from the driver – sometimes good and sometimes so bad that the crackle from the driver sounds like the speakers blew at an AC/DC concert. Even on TV you hear about 1/8” adjustments during Cup races that take the driver from waving handfuls of steering wheel to driving with one hand. Of course, the same team can try to cure a small tight feeling and raising the bar the same 1/8” can make the car...read more »
Since the Panhard/J-Bar is such an important locating device it is critical that the hardware is solid. Any flex creates unpredictable variables resulting in a car that is erratic. The hoop style shown adds rigidity and creates a solid feel for the driver.
Then we get into Panhard/J-Bar split and reverse split. There are a lot of thoughts on this topic. I hear about how teams think the rear end moves left when the right side of the Panhard/J-Bar is higher than the left. Well – the rear end is stuck on the ground and what is really happening is that the frame and body are moving to the right. Your team needs to think about the trailing arms and the rear steer in relation to the amount of split you are running. You also need to think about your shock angles. If they are perfectly vertical on your coil over car then when the body/frame moves right not much happens as both coilovers shorten by the same amount. If you have the top of your coil over tipped in then as the body/frame moves right you are losing diagonal weight as the car rolls and then gaining it as it rolls back. With tipped in at the top coilovers, if you run reverse split, the body/frame moves left and the LR shock gets more upright adding diagonal weight percentage.
Still, there are many times when you add reverse split that the car turns better even though there is potentially more diagonal through roll. The big reason is that the Panhard/J-Bar was probably too high to begin with and side bite is lost. The car skates in this scenario so lowering the bar creates more grip. More grip allows the driver to feel more secure so he can simply turn the car to the bottom instead of skating up to the second groove. Sure – you can think about how reverse split encourages the rear end housing to be pulled into the track and how standard split (higher on the right side) pulls up on the rear end housing. Last I checked gravity is the same and regardless of how uphill you run the Panhard/J-Bar so I doubt the rear tires will ever fly off the ground due to Panhard/J-Bar angles.
With standard split or reverse split rear steer comes into play. You can use rear steer to your advantage but remember to think past direction the housing moves through roll. Keep in mind that the housing goes the opposite way as the chassis unwinds and sometimes the opposite and equal reaction is more important than the intended action.
Frame side Panhard/J-Bar mount
A frame side Panhard/J-Bar mount that adjusts quickly can maximize practice time ensuring you have every chance to dial in the car. The slider version allows for precision locating and increments as small or as large as you need.
Even so, there is still more to it. The goal is to get the most out of everything. Maximum down force in combination with soft tires creates an opportunity. Of course, you may have a sway bar in the car the diameter of a sewer pipe so how do we balance the Panhard/J-Bar in association with a ton of rebound in the front shocks and a sway bar that locks down the nose? Again, there is not an answer as “all” of the variables have to come together to create the right feel for the driver.
A J-Bar bracket with a slotted adjustment allows for quick changes. A wide adjustment range with slots verses holes will help your car to find every ounce of speed.
Instead of me telling you the answer to the pop quiz I prefer to write down my thought processes. It makes little difference if you agree – it makes a lot of difference that you develop a consistent system that lines up with the variables that you face. Honestly, the magic 48 has mastered this systematic approach. Sure – they make a ton of horsepower but in the end the 24 and 88 have the same junk. The 48 kids have balanced the HP with the aero, the shocks, the sway bar, the available grip and have come up with a system that allows Jimmy to run aggressive rear weight and ideal Panhard height. I don’t have inside knowledge - but I “know” that Jumping Jimmy, whether y’all like it or not, can run aggressive set ups that push out every ounce of grip cuz Sir Knaus has this formula flat figured out. He approaches the system the same way every week and eliminates as many variables as possible. The result is an edge that allows his team to be better than team mates that are in the same shop. The benefit is that Jimmy can get a little more due to the communication derived from their proven formula that features the Panhard height as a major component in their magic math.Raise the Panhard/J-Bar when:
- There is a ton of grip available.
- When you have high amounts of down force.
- You have high banking and smooth transitions.
- When the car is solid and easy to drive deep into the corner.
- When the driver can pull down a groove at will.
- The driver doesn’t like the corner entry feel.
- The car won’t stay on the bottom.
- The track is bumpy or has little grip.
- When the car feels fast for 2 laps then drops off considerably.
- When left side tire temps are low.
- The driver says the car is tight yet you have thrown many adjustments at the car that should have made a noticeable difference – none of those adjustments are working. This may be a time when a lower Panhard/J-Bar can add more positive rear steer through added roll helping it to turn in the center. A gain in side bite would be the goal increasing overall grip giving you new chassis adjustment options created by this new baseline.
- The car needs more side bite so the driver is timid with the steering wheel on corner entry so he misses the apex making him believe the car is tight. Pay special attention if the driver complains that the car snaps loose after being tight in the center as this “can” be an indication that lower is better.
- When you keep raising the bar to help the car turn and there is little change.
- Panhard/J-Bars are so easy to move that sometimes it pays to simply raise and lower it a small amount and just use the trial and error method.
Why do we need a caster? The most direct answer is for directional stability. Without caster our racecars would wander, in an unstable fashion, on the straights and be hard to handle at high speed corner entry. Positive Caster allows the front wheels to trail behind the caster line for true tracking. Extending a line from the top ball joint though the bottom ball joint creates the caster line or caster angle. If the line extends forward of the lower ball joint...read more »
Caster is measured in degrees
Caster is measured in degrees. When a line is extended from the top ball joint through the bottom ball joint the caster line is created. Zero caste would be when the upper and lower ball joints create a line that is perfectly vertical. Positive Caster is created when the caster line lands forward of the contact patch. Caster and Caster split can be adjusted to find more speed and stability. A common example of caster is a shopping cart. As the shopping cart is pushed forward the front wheels spin back and trail behind the caster line.
Caster creates stability as the geometry created forces the wheels back to straight. The front wheels are “encouraged” to stay straight as turning them involves lifting the car weight. Expensive street cars often have high amounts of positive caster providing them with a superior and stable feel. The drawback comes in the form of added steering effort. The invention of power steering has allowed for more caster to be added. When power steering fails it is easy to see the negative effects. As soon as the dripping wet driver gets out of the car and asks for help opening a beer due to his arms being worn out it becomes clear how power steering has allowed higher amounts of caster.
In stock cars, we can use caster to help our cars going beyond simple directional stability. Caster split is often used as a chassis adjustment. Running more positive caster on the right than on the left is common. The question is how much split and how much positive caster should you run?
Caster split and the appropriate amount chosen is one of those chassis adjustments where there is not a magic amount or a right or wrong answer. If you understand the effects of caster split you can make your own decisions based on your track, driver and goals. Commonly crew chiefs run 3 degrees positive on the right side and 1 degree positive on the left side. At times it may pay to run 4 or 5 degrees on the right and .5 degrees positive on the left. It all depends on what you are hoping to accomplish for your specific chassis needs.
An often overlooked element relating to stock car caster is that the more positive caster you run the more “beneficial” camber gain you will get. As the car rolls you will see more negative camber gain on the right side and more positive camber gain on the left in lock step with running additional caster. Camber gain through travel is typically a good thing but like all adjustments you want to avoid going too far. If you are aggressive with A-Arm lengths that create high amounts of camber gain you want to be careful that you do not get to aggressive with caster. As always balance applies.
You can find a "speed secret" by understanding that more caster beneficially adds to negative camber gain on the right front and more positive camber gain on the left front. You can check this effect by measuring your camber gain at your current setting and recording the numbers. Next - add caster and check your camber gain again and you will see the benefits visually right in the shop. With the knowledge you can tailor your set up package to overcome obstacles presented by your car, track and driver.
To visualize the benefit of the caster induced camber gain it pays to think in extremes. If you are running 3 degrees of positive caster on the right this would be in the normal range. For our visualization, picture adding caster until the caster line is adjusted an exaggerated amount until it becomes completely horizontal. At this hypothetical and exaggerated point, the result would be pure camber change instead of directional change. The benefit is that with more static caster, the right front wheel would gain more negative camber as steering input is increased. The left front wheel gains more positive camber as the wheel is turned. Cool, we get more camber gain when we need it most by running more caster through a left hand turn! Even experienced crew chiefs can be unaware of the relation to caster and beneficial camber gain in left hand turns. Personally, I find understanding the camber gain from caster to be a true “speed secret”.
Running more caster on the right side verses the left is an adjustment tool that can help cars turn left. The amount of caster split can create benefits as the wheels are turned. More split will “de-wedge” the car at maximum steering input helping the car to turn in the middle. As the steering wheel is un-wound - wedge is added back helping the car to hook up better on exit. Wedge is added back as the wheels return to straight or even back through to the right. You can easily see this change when you have the car on scales. The next time you weigh your car and you have recorded your race ready numbers simply turn the steering wheel 10 degrees left and you will see your scale numbers display less wedge when the wheels are turned left.
Use turn plates to help measure caster
You can use turn plates to help measure caster. Using a quality caster camber gauge the turn plates allow you to turn the wheels exactly 20 degrees for precise caster measurements. You can also use the turn plates to visually see the caster induced camber gain when running higher amounts of caster. Simply check the camber gain with the wheels straight and compare the camber gain numbers to your results with the wheels turned 10 degrees left.
Based on the prior paragraphs it would make sense to run high amounts of caster and plenty of caster split yet understanding the concept will create speed whereas just throwing in aggressive settings could set introduce problems – it pays to understand your changes in advance. Too much of a good thing leads to trouble. There are many variables to consider when it comes to caster amount and split. You must consider other geometry choices such as A-Arm length to avoid ending up with too much camber gain. Too much split can make the car pull too hard to the left making the car tough to control in traffic and on corner entry.
You can thank power steering for creating options with high amounts of caster. Power steering overcomes the steering effort and in the past high amounts of caster was simply not possible as the effort required wore out the driver in a handful of laps. Prior to power steering it was quite common to run negative caster on the left front to reduce steering effort.
For less experienced drivers, I recommend running as much caster split as you can get away with. Something in the neighborhood of 4 positive on the right and 1 positive on the left will help your rookie driver. The idea is that the split will help them to catch the car when it gets loose preventing them from spinning out. As the rookie drive unwinds the wheel wedge is automatically added back in giving the rookie a little help anticipating the loose car before they go for a ride. The split gets wedge back in the car quickly as they correct back to the right giving them security and a helping hand. For rookies, I might compromise my faster caster set up to ensure they finish races. Giving rookies caster split builds their confidence and helps to prevent them from getting behind on the steering.
Use slotted A-Arms
On most stock cars the top A-Plate is set back to build in the positive caster that most people run. Using slotted A-Arms and slugs makes for quick and consistent adjustments at the track or in the shop.
For experienced drivers, that have a good feel, I might reduce the caster split. The chassis premise is that you know your good driver and you can allow him or her to drive the car without interference from overdone geometry. Again, there is much to consider and other chassis goals would easily override this choice. The experienced driver feels the car and sometimes wants the control in their hands as they anticipate with confidence. In this case, they want to turn the wheel for the desired effect verses being forced into a geometry change that happens outside of their steering input control.
I would push the window on caster amounts and splits on tracks that are smooth and with sweeping corners. If the driver can consistently turn in and unwind the wheel smoothly then adding caster and split can help find speed due to the geometric benefits discussed.
All that said – caster and caster split is very much car, track and driver specific. In much of the country our short tracks are worn out, bumpy and the corner transitions can be abrupt. For rough tracks where drivers are constantly sawing on the wheel, too much caster and caster split can cause the car to be erratic. All the directional change from a steering wheel that is being turned back and forth quickly will upset the car. You can imagine that turning the wheel quickly back and forth would inconsistently put wedge in then out, back and forth steering input would add camber gain then abruptly take it out.
At rough tracks or if your driver nervously saws on the wheel – you will definitely create too much of a good thing resulting in a car that never knows quite what to do and stability is lost. Many of the races my cars won were on rough tracks and I commonly ran 2 degrees positive on the right and .5 degrees positive on the left. The idea was to keep the consistency in the car over the bumps and through quick back and forth steering input. I truly believe this to be one of my speeds secrets at rough tracks. Maybe my competition was being aggressive with their front end settings causing their cars to fade later in the race on the worn out surfaces. That is why they throw the green and checkered flag as there is not a right and wrong here but simply a competitive choice.
Your team can analyze your track, car and driver to see if the benefits of added caster and caster split would overcome obstacles that you face. Used properly there is plenty of speed to be found in the correct caster settings. Your job is to understand the changes through chassis roll. Through understanding you can use caster to create speed and your additional “planned” choices will give you an edge over your competition.
Bump Steer & Bump Stops
Under maximum corner load, where races are won, excessive Bump Steer can slow your car down and make it more difficult to find the optimal set up. Understanding Bump Steer will increase corner speed and give you more options in finding the winning set up.
What is Bump Steer? Bump steer is the toe in and toe out of your front wheels created by the up and down movement of your suspension. Really – bumps aren’t even needed! When the nose lifts...read more »
(Fig.1) Carefully engineered pivot points, angles and lengths
(Fig.1) Your car builder carefully engineered the pivot points, angles and lengths. Setting the Bump Steer is like Blue Printing the suspension to exactly match the design specifications.
The layout, lengths, and angles of the upper A-Arm work together with Lower Control Arm to encompass what engineers refer to as an Instant Center. To help understand the Instant Center you can visualize a triangle (Fig. 2). Draw a line from the center pivot of the top ball joint down to the center pivot of the lower ball joint. Now draw a line from the center of the top ball joint through the inner A-Arm pivot and extend it towards the middle of the car. Complete the triangle by drawing a line from the center of the lower ball joint through the inner pivot of the Lower Control Arm and extend it to the spot where it meets the Upper A-Arm line. The intersect point of the two lines is the Instant Center of your suspension. The RF and LF have independent Instant Centers.
(Fig.2) Your pivot points work together and intersect at the Instant Center
(Fig.2) Your pivot points work together and intersect at the Instant Center. The illustration shows the RF suspension from the front view.
With your triangle drawing (Fig 2.) you can imagine a very long tie rod – one so long it would not fit on a late model as we know it. Connect your imaginary long tie rod with a mental bolt at the Instant Center. Extend your imaginary tie rod out towards the spindle and connect it to the center of the line between the upper and lower ball joint. With this layout you can see that the imaginary tie rod would follow the same arc through travel as the suspension (upper and lower control arms) and the car would achieve zero Bump Steer.
Matching the arc of your actual suspension to the arc of the tie rod completes a design scenario that points your tires straight ahead through suspension movement. To apply the matching arc concept to the design of your late model you will need to consider three design principles for ZERO BUMP.
- Your outer tie rod pivot must fall on a line drawn through the upper and lower ball joints.
- Your inner tie rod pivot must fall on a line that is drawn through the Upper A-Arm pivot and Lower Control Arm pivot.
- The angle of the tie rod must create a line that when extended intersects with the Instant Center.
Race cars are made from welded steel that bows and twists from the heat of welding. Rack plates, steering box mounts and spindles all can have variations that we need to account for by utilizing shims to locate the pivots considering our 1-2-3 design elements. Setting the Bump Steer is like blue printing an engine – you are simply going the extra mile to match your car exactly to the car builder design specifications (Fig 3.).
(Fig.3) Typically Stock Car tie rods follow the Lower Control Arm line
(Fig 3.) Typically Stock Car tie rods follow the Lower Control Arm line. In our drawing we are illustrating that you can mount the tie rod elsewhere as long as the outer tie rod end falls on the Ball Joint Axis line, the inner tie rod end falls on the Upper A-arm and Lower Control Arm pivot line – and the angle of the tie rod ends intersect with the Instant Center.
Often rack plates are mounted too low for direct mounting of the rack. To achieve the proper pivot points detailed in our 1-2-3 instructions we may need to space the rack up (Fig 4). Using CNC machined billet rack spacers adds to the precision or simple washers can be used if you have the correct thickness on hand. Shims may also be needed on the spindle side to account for caster changes or spindle variations.
(Fig.4) Mounting the rack at the proper height allows for zero Bump Steer
(Fig. 4) Mounting the rack at the proper height allows for zero Bump Steer.
To measure the Bump Steer you need a precision Bump Steer gauge and you will find a digital version speeds up the project. Suspension settings need to be racing ready and the proper components need to be fully installed and tightened. All front end settings need to be set – exactly. Tackling the Bump Steer measuring process should only begin when the car is truly race ready. Prepare your car in the following order and consult your car builder for their recommended front end specs. Make sure you have the right parts on your car!
(Fig.5) A faster and more accurate Bump Steer process
(Fig. 5) A Precision Bump Steer Gauge that is billet rigid and utilizes one dial indicator will do the math for you for a faster and more accurate Bump Steer process.
Prepare the car to measure your Bump Steer per the following Check list:
- Set the tires – air pressures and stagger.
- Set the ride height.
- Adjust the camber.
- Adjust the caster.
- Match your tie rod lengths per the1-2-3 instructions.
- Center the steering by centering the inner tie rod ends with the Lower Control Arm inner pivot per the 1-2-3 instructions. Lock the steering in place to ensure solid measurements.
- Set the toe.
- Record a reference point while your car is on the ground and at your design ride height. Measure from the floor to the lower grease fitting or other repeatable spot such as the sway bar mount on the lower control arm – remember to write the number down.
- Place the car on jack stands matching your ride heights and adjust for the jack stand height. The goal is to maintain your suspension angles while on jack stands matching the ride height on the ground.
- Bolt on the Bump Steer plate to the hub and set it to level. Jack the suspension to ride height and note where the dial indicator touches the Bump Steer plate. Setting Bump Steer is a trial and error process and noting where the dial indicator touches the Bump Steer plate indicator marks will allow you to return to your ride height quickly after attempted adjustments.
- Jack the suspension fully through compression with bump stop set ups (or at least 2”) and through at least 2” of rebound travel. Write down your results and refer to the Quick Shim Guide (Fig. 6).
- Shim as needed.
(Fig.6) Quick Shim Guide
To help you shim your way to proper Bump Steer here is a Quick Shim Guide that you can use after taking an initial Bump Steer measurement (Fig 6):
Bump Steer is stated as X amount of Bump Steer (in or out) in 1” of travel. The starting point for measuring Bump Steer is your static ride height. In today’s world of bump stop set ups the reward for zero Bump Steer is even greater. Bump stop set ups allow for more travel – in fact bump stop set ups use all of the travel! More travel multiplies Bump Steer geometry errors and spending the time to get it right does mean more speed and more importantly it produces a fast car all the way to the end. Why fade when you can win? Is improper Bump Steer one of the reasons why some cars slow down at the end of races?
If you have excessive Bump Steer you are un-necessarily heating your tires and wearing them out. The tires go over the bumps in a very fast manner and those millions of in and out toe oscillations generated by too much Bump Steer produces un-wanted tire heat and instability. You can think of it nearly as a toe vibration – in and out – back and forth in rapid motion. Remember, the movements occur through travel not just from bumps. Braking, acceleration, roll, transition all create movements that will magnify Bump Steer. Get rid of Bump Steer and let the driver turn the wheels verses letting the tires turn unpredictably on their own!
So – now that we see the Bump Steer light it is time for the golden question. How much Bump Steer should we run? It’s a matter of opinion and every set up guy has their magic formula. My answer is as close to zero as possible. What ever Bump Steer amount you use should be a recorded and repeatable number that is adjusted verses being an accident. Repeatability in race set up is the way to go.
A small amount of Bump Out is stable. Bump In can cause an unstable car – I always stay away from Bump In. A small amount of Bump Out ensures that my cars avoid Bumping In. A small amount of Bump Out ensures that you avoid Bump In through component flex and it covers unforeseen variations. With Bump Stop Set Ups and Big Bar Soft Spring Set Ups my recommended number is .004 of Bump Out per 1” of travel both left and right.
Before Bump Stop set ups - utilizing a common set up in a 2900 pound touring late model my base Bump Steer set up was .002 to .005 of Bump Out on the RF and .005 to .008 of Bump Out on the LF. Consult your car builder and use his experience. Remember, every car builder has their own idea of Bump Steer settings. Consistency and repeatability are the goal.
“A qualifying trick is to bolt in an extra .187 shim on the LF for your qualifying run which adds about .010 of additional Bump Steer at the LF for a qualifying total of .018 verses my standard .008. Sticker tires and their extra short term grip cover the negative effects of the added Bump for a lap or two. The benefit of the extra Bump Steer is that it manufactures some quick heat in the LF. Under the stress of a one or two lap banzai run the added LF quick heat helps set the car into the middle of the turn - sticker tires make it work”.
Rolling through the center of the turn at maximum speed requires a suspension that is free of flex yet moves smoothly with out binding. A-arms have improved dramatically and choosing the correct A-arm will help you to create suspension systems that are faster and more consistent.
There are many things to consider when selecting the A-arm for your car. For dirt cars many racers have utilized arms that split at the bolt in ball joint allowing the a-arm to be...read more »
Billet A-arm spacers
Billet A-arm spacers help to maintain your settings when making changes at the track. These tapered shims keep your A-arm shaft straight preventing binds.
Machined A-arm spacers have replaced the days of caster camber washers falling all over the ground. A-arm spacers can be purchased in straight or tapered styles helping to keep A-arm shafts straight eliminating binding.
A-arm nut plate
To further speed the job many teams use a A-arm nut plate that holds the backing nuts allowing use of one ratchet on the front side. Crew members appreciate avoiding the hot headers while holding an end wrench at an awkward angle.
Beyond choosing a slotted version or the basic single hole version, special attention should be paid to the tolerances between the steel A-arm and the shaft. The tolerance is critical as not enough clearance leads to binding and galling. Too much clearance creates unwanted movement and caster change especially under braking. At times excessive clearance can lead to chattering and an unstable car. In dirt applications too much clearance can allow dirt to crawl between the housing and the shaft and the grinding action causes premature wear, sticking and increased friction. Quality A-arm manufactures hold the tolerance for optimal performance.
4 Bearings spread out the load
4 Bearings spread out the load and this version has a machined bearing housing to keep the shaft in perfect alignment for lower friction.
As the suspension rolls and rides over bumps the A-arm is worked up and down continuously. For more consistent performance many teams are going to bearing style A-arms to eliminate friction. Teams are finding that with roller bearing A-arms that they can sometimes run slightly less spring rate due to the reduced friction. A-arms last longer as the bearings prevent the wear created by the steel A-arm tube contacting the shaft. Heat expansion from the headers and brakes can negatively affect standard A-arms if manufacturers do not use proper clearance. Bearing A-arms effectively eliminate the heat issue.
Bearing Style A-arms reduce friction
Bearing Style A-arms reduce friction for smooth roll and repeatable performance on the track. This version has a machined bearing housing allowing racers to replace just the steel tube section for quick adjustments or crash repair.
The smooth action of the bearings builds consistent suspension roll and increased corner speed is obtained over a long green flag run. The tight tolerance and low friction of bearing style A-arms eliminates variables allowing crew chiefs to make chassis adjustments with the assurance that the suspension is rolling up and down in a repeatable free flowing fashion. Removing the binding found in less expensive A-arms creates speed as the adjustment decisions are not chasing inconsistencies. Each crew chief decision becomes more effective and every racer should strive to eliminate variables for consistent speed week in and week out. Quality A-arms are powder coated for a premium finish where as less expensive models are spray painted which quickly wears off.
Adjusting the car with A-arm length can be very successful. Shorter RF A-arms create more camber gain and might help you to improve your tire sheet readings. Shortening the RF A-arm moves the front roll center up and to the right. At times the quicker reaction of the RF suspension, due to a shorter A-arm, can improve lap times. Experimenting at your track with A-arm length is just as effective as making a spring change. New A-arms on the market allow you to change the steel A-arm tube section while leaving the shaft bolted to the frame. These new designs speed trackside changes and reduce costs as racers can carry different A-arm tube sections without the added expense of extra shafts.
Big Bar Set Ups generally use longer A-arms than conventional set ups. Camber gain adjustments that line up with your Big Bar Set Up is a critical piece to the puzzle. At times teams jump between a conventional set up and a big bar set up. The A-arms with a bolt on section speeds the A-arm changes that are needed.
Utilizing low friction ball joints with your bearing style A-arm further enhances free movement of the front suspension. Some low friction upper ball joints are adjustable giving racers another adjustment. Fine tuning A-arm angle with the upper ball joint allows for quick roll center adjustments and easy experimentation. Adjustable upper ball joints can be used in conjunction with slotted frame A-Plates. Slotted A-plates allow the inner pivot of the A-arm to be moved up and down and slugs secure the inner pivot in place. The A-Plate slugs are manufactured for precision adjustment in the up/down axis offering another roll center tuning tool.
With out a proper weld bead flex and cracking can occur
The weld on this A-arm is suspect. With out a proper weld bead flex and cracking can occur. High quality A-arms use thick wall .095 tubing and are TIG Welded.
Some A-arms flex more than most race teams think. Prominent teams test the flex of new A-arm brands before they end up on their car. Manufactures that use thick wall .095 tubing know the slightly more expensive tubing reduces flex as compared to .083 which is commonly used. TIG welding is another feature that will reduce flex. Poor quality wire feed welds make for limp noodles verses a rigid A-arm system. Be sure to inspect the weld quality before purchasing A-arms for your rocket.
We built this fixture for this test which can apply from 0 to 1500 pounds of force right at the ball joint emulating the conditions seen on your car. We can also set up the fixture to cycle A-arms repeatedly for destructive testing.
Shaft type has an effect on flex. Choosing lightweight aluminum for the cross shaft comes at a price – aluminum flexes more than steel and racers should consider if the few ounces of saved weight in an aluminum cross shaft is a good trade. Our test results show that the steel shaft attached to a 9.5” A-arm flexes .110” at 600 pounds of force where as the aluminum shaft flexes .150” at the same force.
Custom flex testing fixture
For this test we used our custom flex testing fixture applying force ranging from 200 lbs to 750 lbs. The dial indicator illustrates the flex difference between top brand A-arms and less expensive imitations.
A-ARM Flex Chart
- 9- ½” Bearing Steel Shaft No Name Brand
Flex at 200lbs = .060, at 400 lbs = .100”, at 600 lbs = .135”, at 750 lbs = .155”
- 9- ½” Bearing Steel Shaft Quality Brand
Flex at 200lbs = .040, at 400 lbs = .075”, at 600 lbs = .110”, at 750 lbs = .130”
- 9- ½” Bearing Aluminum Shaft Quality Brand
Flex at 200lbs = .056, at 400 lbs = .105”, at 600 lbs = .160”, at 750 lbs = .200”
- 9- ½” Alum. Shaft (no slot) Quality Brand
Flex at 200lbs = .056, at 400 lbs = .105”, at 600 lbs = .160”, at 750 lbs = .200”
- 9- ½” Steel Shaft (no slot) Quality Brand
Flex at 200lbs = .050, at 400 lbs = .075”, at 600 lbs = .110”, at 750 lbs = .130”
- 9- ½” Steel Shaft (no slot) No Name Brand
Flex at 200lbs = .090, at 400 lbs = .125”, at 600 lbs = .185”, at 750 lbs = .225”
Our fixture for this test was designed to apply varying pounds of force. The flex chart shows the movement associated with applying lateral pressure at the ball joint center line. The fixture is rigid and the frame mount is the same as you would see on your car. The goal in building the fixture was to emulate what your A-arms see in your racer.
Teams that reduce friction and flex will take another step forward. Racing continues to evolve and teams demand better pieces to find speed. Luckily manufactures are stepping up to the challenge.
- 9- ½” Bearing Steel Shaft No Name Brand
Finding speed a little at a time is the way to the front. A few horsepower here, less drag there coupled with a good shock change might add up to half a tenth on a good day. Reducing rolling resistance is one of those speed secrets that works continuously but it is hard to measure in the real world. Still – if your car has less rolling resistance common sense dictates that your race car will be faster.
Cup teams go to great lengths to measure...read more »
What is the right amount of oil?
When running the hubs wet it is important to add the right amount of gear oil. 4 to 7 ounces is recommended by the car builers we surveyed and your team should monitor the fill level to ensure proper coating of your bearings. High quality synthetic lube is required.
You can experiment with the right amount of oil if you run your hubs wet. Zaretske recommends 4 ounces but other builders and hub manufactures may have their own recommendation. Our survey of car builders resulted in a recommended hub oil fill range from 4 ounces to 7 ounces utilizing synthetic fluid. As running hubs wet is a new speed secret you should keep an eye out as the fill level recommendations will change based on testing, fluid type and the evolution of manufactures specifications.
Low friction roller bearings or Teflon coated tapered bearings will lower your rolling resistance where you need it most. Roller ball bearings should be inspected often and need continuous maintenance.
Chuck Carruthers of Chuck Carruthers Industries says that only 5% of his customers are running hubs wet. Carruthers states: “Using Teflon coated bearings with 4.25 ounces of 50 weight synthetic gear oil gains 6 to 8 coast down horsepower”. Chuck prefers traditional wheel bearings and pays the extra cost for the Teflon coated version. Chuck feels the low friction roller ball style bearings are risky in long races. Carruthers says; “we get plenty of friction reduction from Teflon coated roller bearings and would rather avoid the added wear seen in roller ball bearings”. At Carruthers Industries they are careful and run the minimum amount of hub oil to ensure parts are coated but avoid running too much fluid as excess fluid in the hub can actually add heat. Chuck says “you want enough fluid to coat the bearings but any surplus fluid can foam or even impact how heat transfers and dissipates through the hub”.
Weekly draining and refilling of "wet" hubs is simple. Fresh oil helps your parts and their longevity. Using a locking hub nut will ensure that your hub maintains torque even at lower torque settings.
With the “wet” system and Teflon coated bearings Chuck recommends running 15 to 20 ft pounds of torque on the front hubs. He advises that you can run less on the rear as the brake heat is less intense. Chuck says 10 to 12 ft pounds on the rear hubs works great. Reduced preload on the bearings reduces rolling resistance creating more speed. Chuck reminds us “be sure to use a locking hub nut to ensure your torque setting stays put from cold to hot”.
Carruthers pays attention to detail and has made a special hub adapter for measuring hub torque. Chuck advises: “When our customers are doing their own work we have them torque the hub nut to our recommendations with a good foot pound torque wrench – we give them the setting and they simply torque down the hub nut and lock it down. For the cars that we maintain in our shop we go the extra mile and use a hub adapter that connects to a high quality inch pound torque wrench – the adapter connects to the torque wrench at the hub center. We add oil and give the hub a spin ensuring the hub and seals are lubricated. We then use our inch pound torque wrench with our custom made centering adaptor. We adjust the hub nut until we have 28 inch pounds of drag torque when rotating the hub with the torque adapter at cold temperature. When the hub is hot we know that there is minimal torque on the hub providing for optimal reduction in rolling resistance. At race temp we see about 3 to 4 inch pounds of drag torque with our custom measuring device”. Care should be used with this process as if the specs are not followed exactly you could end up with too little torque resulting in failures. Weekly inspections and pre-race checks are needed when pushing the edge in this fashion.
Using a floating rotor with a T-Nut package allows the rotor to expand through the heat range. The movement allowed by the rotor flange is isolated from the hub resulting in less drag. This hub has a seal retainer system that lets you remove and replace expensive low friction seals with out damage.
While at the 2008 PRI show a confidential source explained the secret testing their team performed relating to floating rotors. Since my confidential source did not want to get fired by his team he wants his name kept out of this article. The secret tests performed by his high profile team revealed that running floating rotors added 6 horsepower on the chassis dyno. Making 6 horsepower due to brake efficiently – seems crazy! The HP gain is due to the floating rotors finding center through out the heat expansion range. The T-nut set up and rotor flange allows for a bit of movement that absorbs rotor warping and isolates it from the hub resulting in less brake pad drag. You get the horsepower gain and the brakes run cooler due to less pad and rotor contact. Drivers report smoother braking with reduced pulsing adding to the efficiency of the braking system. Here we go – a little more speed created by removing unwanted friction.
Another way to reduce rolling resistance is to square your rear end. There are many thoughts on rear end set ups but I like to keep this simple. I make sure my rear tires run nearly parallel and make sure the rear end is set square in the car. When building a rear end I make sure both tires point straight ahead and then I toe in the RR tire 1/32 of an inch. I figure at speed and under load that the RR will pull back that much and when it counts the rear end is perfectly square. A square rear end will not have any drag as compared to running toe out with the tires dragging all the way around the track. We know Cup teams play around with rear toe settings for aero advantages but for short track racing a square rear end will be more consistent and it will reduce your rolling resistance.
Equally important is the front toe setting. It is common for short track racers to run 1/8th inch or so of toe out and this spec has been around as the standard for a long time. I think the thought process is different now as compared to a few years ago. Today I recommend rethinking the toe out setting in the front end. Our components are simply manufactured better today and there is less free play in the front suspension pieces. A-arms are stronger, racks are better, rod ends, ball joints and tie rods are all built with tighter tolerances. I would recommend running 1/32nd of toe out or even zero toe out in the front. With the tires pointing straight ahead you can find more speed and eliminate tire drag from excessive toe out.
Ackerman should also be considered. Ackerman is sometimes used as a chassis adjustment but the Ackerman effect and additional degrees of steering at the left front tire creates drag. Keep in mind the amount of tire drag you are adding to the car if you have Ackerman toeing out the LF tire as you turn. Excessive Ackerman can sometimes cause a hitch when the driver picks up the throttle. As the power is applied to the rear tires they have to push against and overcome the Ackerman drag on the left front. Depending on the situation the car may break loose or simply not leap off the corner due to the Ackerman drag. Ackerman can be a great adjustment but thinking out the rolling resistance considerations may find you additional speed.
Aerodynamics is another area where rolling resistance gains can be found. Air likes to follow body surfaces and air needs smooth transitions to prevent unwanted turbulence. When ever possible create smooth and rounded body transitions verses letting air fall off of sharp corners or cliffs. When massaging air try to mold the body to allow air to follow surfaces avoiding surprise edges or cliffs.
As race cars have evolved reducing rolling resistance may help make up some of the power limitations created by crate motors, 9:1 compression motors, and carburetor rules. Embracing rolling resistance and massaging your car with a friction free approach may “find” you 15 to 20 new horsepower. If you are running a 400 horsepower crate motor you could end up with a net 5% improvement in power! Even with unlimited horsepower the teams that work hardest on reducing rolling resistance will create horsepower that just might be the nudge you need to get you ahead at the photo finish.
Nice Rear End
Getting to the front often start with a good rear end. Today, there are many options and choosing the right rear end type for your team is the goal.
To help your team choose the correct rear end type for your car, I interviewed Frank Loverock of Quick Change Exchange. Frank manufactures ratcheting rear ends and differentiating rear ends and he has provided a wealth of information for this article. In addition, Randy Larsen of DPI added thoughts relating to...read more »
The Locker (Ratchet)
The Locker (Ratchet) allows the wheels to unhook one tooth at a time on corner entry. The “ratcheting” mechanics allow the LR to roll in the corner in conjunction with the RR helping to overcome the negative effects of stagger on corner entry. As soon as any amount of throttle pressure is applied, the locker (ratchet) locks up and performs like a spool. Both axles are locked together and when the power is put down a ratchet and a spool work the same.
Differentials utilize a series of gears that apply the power to each rear tire individually
Differentials utilize a series of gears that apply the power to each rear tire individually. Less stagger is required and if your stagger changes the differentiating action works to keep the handling characteristics of your car the same throughout the race. A differentiating rear end has moving parts that require regular maintenance. Quality gear oil is needed and performance can be changed based on the type of oil used. Coolers are highly reccomended when you run a differential style rear end unit.
Differentials apply power to each wheel independently and the need for stagger is reduced. The axles are not solidly connected together and internal gears apply power to each tire separately. The result is a rear end that compensates for stagger changes. The car is more consistent and self adjusts for changing corner conditions.
Racing differentials feature an aluminum housing for lightweight. Manufactures are always discovering new ways to improve performance while producing lighter weight parts. Unit's of today do more and weigh less due to design improvements and superior machining techniques.
Q: As compared to a spool – why is a locker a good choice?
Frank Loverock: The benefit of a locker is improved corner entry. As you roll into the corner, without any throttle pressure, the car enters the corner and the effects of stagger are basically eliminated. Both tires roll in equally as specially designed springs control the ratcheting action. At entry, the LR is connected to the driveline and the right wheel ratchets forward creating an entry without effective stagger. The car never freewheels, either one or both rear tires are connected to the driveline. The instant you push the throttle the ratchet locks up and you drive both rear tires 100% just like a spool. A locker (ratchet) is a spool 90% of the time so it is a myth that you can run less stagger.
Randy Larsen: A locker can help a car into the turn and reduce an entry push. The rear tires ratchet in a controlled fashion for a more stable entry. Since LR isn’t dragging entering the turn, drivers can drive in deeper. A locker becomes a spool as soon as the driver hits the gas so stagger settings are critical. Under power, the locker acts just like a spool so your tire guy needs to make sure that the stagger remains perfect throughout the race. Any change in stagger is going to be felt and loss of stagger often will create a nasty center push.
Q: As compared to a spool – why is a differentiating rear end a good choice?
Frank Loverock: On a circle track car, the RR must travel faster and further than the LR due to the larger corner arc on the outside of the track as compared to the inside. The differentiating action turns the LR at a slower rate helping the car to turn.
Differentiating rear ends offer great advantages but come with significant maintenance so a trade off is made. The benefit is a car that really turns. The rear end may drive the LR 49% and the RR 51% and the unit is always differentiating applying power as needed to the wheel that needs it most. Differentials never drive the LR and RR equally but rather compensate for the ever changing position on the track. In other words, differentials are always driving the appropriate wheel faster than the other eliminating the dragging of a tire down the straight away. The faster turning of the outside wheel gets your car through the center with less dependence on stagger. Spools and lockers drag one tire if you are running even a small amount of stagger.
Randy Larsen: A differential gets you through the center allowing the car to turn freely setting you up for a straight and powerful exit launch. The differential action allows you to run the low groove one lap and the high groove the next as the gear mechanism compensates for the change in corner radius. If your stagger changes - the differential will make up the difference so you car stays fast the entire race.
Since the differential gets you through the center, you can adjust your set up for a tight launch off the turn. The differential gives you more chassis setup options than a standard spool and the driver feel through the center is vastly improved. When your stagger changes a spool driven setup is negatively affected. The torque sensing action of differential units allows the car to roll freely through the center and compensates for changing stagger.
Q: What improvements in design and quality have been added to rear ends?
Frank Loverock: Superior machining operations create parts that mate together precisely for smooth long lasting operation. Better materials coupled with sophisticated heat treating processes create unparalleled longevity and performance. Rear end units last longer and work better through exploitation of modern science. Knowledge from the past is applied to what we build today. Historical influence is partnered with advanced modern day processes creating improved product at fair pricing.
Randy Larsen: In racing, heat is nearly always the enemy. New manufacturing processes have allowed components to be light where needed and designers can pinpoint the need for mass at critical areas. Heat treating and CAD software have allowed differentiating rear ends to be optimized as compared to past designs. The optimization results in consistency. Units manufactured today limit and compensate for heat expansion efficiently resulting in enhanced performance.
Q: What rear end types do you recommend to experienced racers?
Frank Loverock: For experienced teams, a locker or a differentiating rear end is a good choice. It comes down to driver feel. Experienced teams are better suited to handle the added maintenance and often have larger budgets. The benefits of advanced rear ends, provides choices for experienced chassis gurus. With better feel, drivers can often get more speed by utilizing a rear end that matches their style, track and set up.
Q: What rear end types do you recommend for beginning racers?
Frank Loverock: For beginning racers I think a spool or maybe a locker is best. It all depends what the new driver wants to get out of their career. If they hope to move up to the top NASCAR divisions then gaining a feel for a locker becomes more important. All the top NASCAR series require lockers so gaining experience is a factor. Lockers require maintenance but the rebuild cost and time is manageable.
I strongly believe that a beginner should keep things simple so the spool is a good choice. As beginners gain experience and understanding grows, then experimenting will help their learning curve. Trying new things will help beginning teams to learn what different adjustments can accomplish. Starting from a simple proven baseline speeds the learning curve. As knowledge increases and drivers become more confident, then replacing the spool with a locker or differential creates a situation where teams can learn and feel the benefits from trying out new ideas.
Q: Coolers, Oil & Maintenance for lockers & differentials?
Frank Loverock: A rear end cooler is highly recommended and the best quality gear oils add to performance. Our group has designed synthetic oils that are specifically engineered for the friction created by the differentiating action. The test time to create exceptional gear oil is unbelievable and regardless of the gear oil you choose, quality is a must.
Randy Larsen: Gear oil choice for differentiating rear ends is an area where spending more is always the best choice. Inexpensive gear oils translate to worn out hardware. We recommend top quality gear oil such as Joe Gibbs. We recommend coolers as reducing heat increases longevity and consistency.
Both Frank and Randy recommend servicing lockers & differentials twice a year based on 25 races under 100 laps. A once a year rebuild “can” be okay. But, stretching service intervals can result in diminished performance. Personally, I would go with twice a year, as a minimum, based on the 25-100 lap race schedule. A locker requires less maintenance as compared to a differential. Ensuring that locker springs hold their designed rate is a must.
Q: How has the use of rear end units changed?
Frank Loverock: Experience has allowed us to manufacture 6 different springs’ rates for locker units. Stronger spring rates give the car a tighter feeling on corner entry. Lesser rates free the car up. Individual drivers often like different feels so over time the need for multiple spring rate options have evolved. Manufacturing processes have improved allowing for all rear end units to create more corner speed. Spring technology allows for ratchets to be custom tailored for specific track conditions or driver styles.
Locker springs are manufactured in a variety of rates to control the ratcheting action for the perfect driver feel on corner entry. A stiffer spring creates a tighter feel on entry and correspondingly a lighter rate spring creates a more free feel.
Randy Larsen: Tolerances control has made giant leaps forward. Differentiating rear ends perform better and last longer. As the manufacturing techniques have improved, engineers can find more speed with components that mate up more efficiently. As the science improves, doors of creativity open. Engineers can take advantage of creative ideas as they can count on sound manufacturing processes that produce components that perform every week.
Q: What other tips relating to rear ends would be important for our readers?
Randy Larsen: Proper venting is paramount to rear end performance. 1/2” hose and a minimum of 3/8” NPT fittings will allow sufficient air volume and rear end breathing. Small hose can cause pressure build up and unwanted problems. Be sure to route your vent line so that oil can drain freely. Kinks and dips in the line will cause oil to pool up preventing proper venting. The vent should be at the highest point possible above the housing. The hose should be routed as straight as possible to avoid areas in the hose where fluid can pool up.
Frank Loverock: We are constantly developing technology and lighter weight differentials are the result. Differentials differ from lockers as they are free from locking and unlocking.
The differential allows you to run less stagger, about half as much as a spool, depending on the track. Differentials are very forgiving in relation to stagger changes as the gear mechanism is constantly adjusting to the current condition resulting in handling characteristics that stay the same throughout the race.
Jeff Butcher: All rear end types offer positive choices. The simplicity of a spool is very often fast, inexpensive and maintenance free. Heat is less of an issue and a rear end cooler is optional at many tracks.
The locker creates stable corner entry. Coolers are needed and correct locker springs will speed your car up. You sign up for maintenance but less is required than a differential.
The differential can do many things to add to speed. In exchange for the stagger compensating differential action, heat is created and since there are more mechanical parts - wear and maintenance need to be considered.
In the end, all three types consistently win races. It is not a question of right and wrong. Choosing the correct rear end is specific to the needs of each team and the goals that they have. My teams have won plenty of races with a spool and if you are on a tight budget the simplicity becomes more important. It was fun to win with the free entry of a locker which is often a great choice. At other times the differential willpower you to the front and that great feel in the center is something that drivers always enjoy. Teams that choose rear ends based on their own needs are making the “right” choice. In racing, bolting in speed is a myth. Having a nice rear end is always a good thing regardless of the type you like to run with.
Why Anti Dive?
Conceptually, Anti Dive is not really a difficult geometric program to understand. Engineers find a way to overcomplicate what is simple. Hey, we need engineers, but our chassis builders build in only so much adjustment for Anti Dive so we really can’t get in too much trouble if we have a basic understanding of the mechanics involved. On a stock car, that has upper A-Arms and lower control arms (like the cars that you see in this magazine), it pays to simplify...read more »
Create a an A-Arm arrangement that is identified as Anti Dive
In this photo you can see that the RF A-Arm is nearly parallel to the frame. If you look at the lower pivot points they are parallel as well. Raising the front of the RF A-Arm, so that the front pivot is higher off the frame (ground) than the rear pivot, creates a an A-Arm arrangement that is identified as Anti Dive.
So, lowering the back of your A-Arms puts Anti Dive in the car – it’s an easy adjustment that you can make right at the track. You can adjust Anti Dive with the lower control arms, but for this article we are focusing on the upper A-Arms so that the concept is the focus. Hopefully, concentrating on the upper A-Arms reduces confusion in our quest to promote a new possibility. The goal is to get you to think out the information so you can see if you want to add adjusting the Anti dive to your adjustment arsenal this week.
Zero percent Anti Dive
This view again shows the A-Arm parallel to the frame, which creates zero percent Anti Dive. you can adjust the Anti Dive with the lower pivots, but for this article we are focusing on the Upper A-Arms so that proving the concept is the focus. The concept is simple, but by taking the lower points out of the equation, for now, confusion is reduced and your understanding of Anti Dive will allow you to understand the adjustment. Once the engineering is understood - you will find that using the lowers to adjust Anti Dive has a dramatic affect and a little goes a long way. The Billet Nut Plate is a cool option that keeps your hands away from hot headers.
If the Upper pivots are parallel to the frame and the lower pivots are parallel to the frame then you have zero percent Anti Dive. You can adjust until you have 100% Anti dive and when the brakes are applied the front end will effectively be locked up and the suspension will not drop at all. The Anti Dive will carry the weight of the car based on the transfer from the rear coupled with the weight transfer affiliation of the Center of Gravity of the car – so there is the science. How about we just slap in some slugs and remove the complicated engineering speak?
Using A-Arm frame mounts with slots allows for the use of slugs making track side adjustments quick and easy. Slugs allow you to make adjustments in 1/8” (or smaller) increments and the solid mount ensures you can repeat adjustments with easy documentation. You can make a change and if the driver likes it then great – if not, a quick slug replacement gets you right back to your baseline. You can save the heavy math and engineering for when you have graph paper and a lot of time at the shop. At the track – simply slap in a slug to make a 1/8” to 1/2” adjustment at the upper A-Arm pivot and you have plenty of adjustment for Anti Dive or Pro Dive right at the track. You can make the change in 5 minutes and the slug system gives you hardware that is recordable and repeatable. Good science always comes with repeatability.
Slugs give you a solid mounting system that is secure and recordable
If you look closely, you will see a slug at the rear pivot of the Upper A-arm. The slug raises the back of the A-Arm as the offset is larger than the front. The slug combination raises the back of the A-Arm and this angle creates Pro Dive. A simple slug adjustment allows you to quickly change the amount of Pro or Anti Dive right at the track. Typically, slugs are made in 1/8" increments so you can run Pro Dive as shown in the photo to help set your car into the turns. The slugs give you a solid mounting system that is secure and recordable.
Now that you see how easy it is to move the A-Arm mounting slug hardware – why should you run Anti Dive? Or, why run Pro Dive? When it comes to racecar suspensions, everything is about timing. Anti Dive is creates mechanical resistance under braking. The percentage of Anti Dive can be drawn out on paper easily in the shop - at the track just toss in the different slugs to accomplish your goals. Under braking, Anti Dive resists the dropping movement at the front end under braking. With the mechanical resistance created by running Anti Dive, you can potentially run softer springs and the Anti Dive will carry you through the braking zone. When you get to the middle and lift off the brakes, the soft springs can allow the car to roll or drop as Anti-Dive is reduced to nearly zero when you are not loading the suspension with brake torque. Remember, the Anti Dive resistance occurs under braking so a bumpy track can potentially cause trouble – Anti Dive works best on smooth tracks. Well, I think it works best on smooth tracks and you will find that crew chiefs have varying opinions on this issue.
To help with the mental picture – if you have your RF A-Arm parallel to the frame, then the A-Arm is free to move up and down without any friction or mechanical resistance. If you were to exaggerate the adjustment and place the A-Arm so that the pivots were 90 degrees to the frame, instead of parallel, then you can see the suspension would be locked and could not move. Since practicality only lets us move the A-Arm pivot about Â½” up or down, in comparison to the other mounting hole on your A-Arm, you can see that the braking force resists movement based on the amount of adjustment that your slotted A-Arm ear allows for. Again, you can get more adjustment on the bottom if you need it, but we are focused on the top for simplicity of proving the concept.
Running a slotted A-Arm frame ear
Running a slotted A-Arm frame ear on your car allows you to use pre-measured slugs that mate perfectly for a secure mounting system. Slugs that are engraved with the offset give you an easy reference so your team can record Anti Dive or Pro Dive adjustments in your set up book. Half inch slugs installed in the front of the ear and at the back of the ear give you a full inch of adjustment in a 6" space. For most purposes, the percentage of Anti Dive achieved with the use of (2) opposing 1/2" slugs is a large adjustment. With Anti Dive - a little goes a long way.
By now, hopefully you have an idea of Anti Dive, but what about Pro Dive? When would you want Pro Dive? If Anti Dive resists the nose dropping under braking then Pro Dive (when the front of the A-Arm pivot is lower than the rear of the A-Arm pivot) helps the nose to drop under braking. On a street car, Anti Dive is put in the right and left side to create braking stability. The same amount is run on both sides.
For racing, running Pro-Dive on the LF with Anti-Dive on the RF can help pull the car into the turn. In effect, the car gets some automatic steering under braking promoting a good set at corner entry. You can experiment with running Anti Dive on both sides, or running Anti Dive on the RF and a bit of Pro Dive on the LF. Simple slug changes allow you to see what works best at your track and with your driver.
Allowing for the ultimate in adjustment and repeatability
Slugs that mate with A-Arm ears are marked allowing for the ultimate in adjustment and repeatability. Simply record the slug numbers and your set up book will contain an easy reference to repeat adjustments.
Considerations that come into play are the amount of braking force – if the track calls for heavy braking then the Anti Dive or Pro Dive is going to be accentuated by the full on brake force. If the track allows for smooth braking then maybe you can run more Anti Dive to accomplish your goal. In general, Anti Dive can help give the car stability at corner entry under braking – when the brakes are released your soft springs can ride over the bumps and roll easily into the turn. Running Anti Dive might allow you to run the soft springs that help in the middle or over bumps as the mechanical resistance created by Anti Dive carries you over the braking portion of the track.
Pro Dive on the LF might help set you into the turn – maybe you will be able to run a little less stagger by using a small amount of Pro Dive at the LF. Potentially, less stagger will keep your car hook up on corner exit? The trick is to mix the amount of Pro Dive on the LF with Anti Dive on the RF to help you overcome a problem without changing a spring that could hurt the car later in the turn. Maybe, the Pro-Dive in this scenario starts the dominos in the right direction allowing you to run less stagger?
Measure Anti Dive
You can also measure Anti Dive by using an accurate level to record the A-Arm angle in degrees. An accurate Digital Level will give you a number that you can record in seconds.
The same holds true for bite, stagger and all of the adjustments at your disposal. If you think out the when and where, Anti Dive can help you to fix a spot in the corner that is giving you trouble you can potentially use Anti Dive or Pro Dive to your advantage. While running Anti Dive is common place, Pro Dive can be a good place to experiment. It is standard to run Anti Dive on both front corners. It is very common to run Anti Dive on the RF with Pro Dive on the LF. All that said – there is no rule that says that Pro-Dive can’t be bolted into both front corners – just be careful that the car is stable under braking. All of my articles hammer on the concept that a car that is unstable at corner entry must be fixed or it is going to be a long night. I never risk a set up that has any possibility of being loose on corner entry – period.
By realizing that Anti-Dive resists movement under braking, and Pro-Dive promotes movement under braking, your team can overcome obstacles with another adjustment mechanism in your chassis set up tool box. Small changes go a long way. Using slugs allows you to make changes 1/8” at a time. 1/8” may not sound like much, but it is 1/8” on a 6” bolt pattern so the degree change is significant. Using a 1/2” slug turned up on the front of the RF A-Arm and a 1/2” slug turned down on the back of the RF A-Arm provides you with a ton of degrees of adjustment. I just write down the slugs dimensions – you can measure degrees with a digital level in about 3 seconds – keeping the article understandable is my goal.
The limitation is not in the hardware, but rather in your need to truly need Anti Dive or Pro Dive to fix a real problem. Just because you can adjust the Anti/Pro Dive doesn’t mean you should. In this case, a little goes a long way and under doing it is better than going overboard. Still – top teams adjust the A-Arm angle with the same mental ease as changing stagger or Panhard bars. Experiment and maybe you will learn a new speed secret for your particular car and track. Or, by understanding the adjustment – you can ensure that your car is assembled properly and the Anti/Pro Dive is set within parameters that your car builder had in mind. Measure, experiment, document and repeat – that sound pretty scientific to me.
Instant Center AdjustmentWhy do we care about the Instant Center in the front suspension? We know our car builder spent plenty of time engineering the proper roll center. Instant Center of the Left and Right side front suspension are a piece in the puzzle that creates Roll Center.
Since I am opposed to over engineering at the track, I prefer to focus on Instant Centers and adjust them with the same freedom that is applied to adjusting the rear roll center. “Just try...read more »
Instant Centers can maximize your Big Bar set up
Timing your suspension travel by balancing spring rate, roll bars and shocks with the leverage created by Instant Centers can maximize your Big Bar set up. For that matter - any set up is benefited by experimenting with Instant Center locations.
Instant Centers are easy to visualize. You find the little spot the same way on both sides of the front of the car. For this review we will take a snap shot of the RF suspension. Your A-Arm is bolted to the frame via an ear that is welded to the frame horn. Your lower control arm bolts onto the cross member. You have a spindle pin and the tire size sets the height of the wheel center off the ground. Your A-Arm is about 7” to 12” long and your lower control arm is probably around 16” to 18” long for your typical late model that has a 63.0” track width. Basically, if you have a stock car, the parts that create the Instant Center are similar regardless of your brand of car.
My goal is here is to eliminate the fear that can be associated with the big pile of details that create the magical Roll Center. Really, roll center is often found at about 1.5” off the ground to 2.5” off the ground for most cars – give or take an inch. The left to right location moves all over the place depending A-Arm length. Of course, as soon as you run the suspension through travel the roll center moves about. With a huge roll bar, the rules have changed and once the car has been pulled down to the ground with your insanely stiff rebound shocks, the roll center and instant centers move around much less as compared to when we had a pair of 350’s on the coilovers and an 1-1/8” bar.
Big Bars require new thinking. Since planting the nose piece to the ground is the new norm, then it would seem that the suspension layout is less important – or is it? With the nose piece held to the ground by huge rebound numbers and a sway bar that nearly eliminates body roll, then why do we care about roll centers and instant centers at all?
While the movements are less, they are still there. We still have dive, roll and plenty of bumps. But, all of those movements happen faster and the distance traveled, once the nose pieces is sucked down, is less. With this “new” information how can we make an effective adjustment utilizing Instant Centers along with shocks and springs?
It pays to think about the mechanical leverage of the Instant Center. Adjusting the Instant Center can be the subtle adjustment that compensates for the reduced actual center of the corner travel induced by giant sway bars. Since the Instant Center is 2 simple lines per side we can visualize it easily. The first line is drawn through the center of the upper ball joint and extending through the inner pivot. Be sure to find the true center of the ball joint provided by your ball joint manufacturer. The second line extends from the lower ball joint through the inner pivot on the lower control arm. Extend both lines until they intersect. Boom – the Instant Center is created. Through suspension travel the intersect point moves based on the length, angle and connection point of the upper A-Arm and the lower control arm. See the accompanying photo for the visual and you will see that Instant Centers are pretty simple to understand.
The Instant Center is easy to visualize right at the track
The Instant Center is easy to visualize right at the track. Simply follow the lines of the upper and lower arms until they meet. Be sure to utilize the actual ball joint center provided by your ball joint manufacturer.
Now examine the RF Instant Center and how we can use mechanical leverage to our advantage. Let’s assume our track width is 63.0". If the hypothetical RF Instant Center is 4 inches off the ground and 3 feet left of the vehicle centerline we end up with about 49.5" (close enough) of leverage. If we make the RF A-Arm Longer and keep the same connection point on the frame ear pivot we move the RF Instant Center more to the left. The longer A-Arm gets flatter and it takes the imaginary line longer to run into the line from the lower control arm. The change lowers the RF Instant Center as well. So, hypothetically, let say we moved the RF Instant Center to left about a foot and down 2" (Since we are starting from a known baseline all we care about is the direction of the adjustment – we can repeat the change by tracking the slugs we use).
A-Arm length and mounting height have a dramatic effect on Instant Center Location
A-Arm length and mounting height have a dramatic effect on Instant Center Location. Carrying an inventory of A-Arm lengths gives you more Instant Center Adjustment choices right at the track.
The longer lever arm created by the adjustment scenario in the prior paragraph compresses the RF spring more than it would have in our baseline set up. The car speed and banking provide the same amount of force, but the longer lever creates more travel at the RF. Really – it is like running a softer RF spring when the chassis rolls. Lowering the RF Instant Center promotes more roll. The longer lever from the Center of Gravity gives an additional boost to roll.
Bolt on tube sections
Bolt on tube sections make quick work out of changing A-arm length. Moving Instant Centers at the track is an adjustment you should try more often. The bolt on tube section is a rigid advantage on snouts where the A-Arm wraps around the frame.
Here is where the fun starts – let’s keep it simple. You can draw your suspension and do the actual math and record it for future reference. For now – let’s just think about the concept. Moving the RF Instant Center to the Left effectively softens the RF spring through chassis roll. But, if you want a softer RF spring, why not just put one in? Well, this is where you need to think about the corner entry, when the car is relatively traveling in a straight line, and the corner middle where the car is in full roll. If you balance the Instant Centers, and consider all of the compromises that come with race car set ups, you can make subtle adjustments by manipulating the timing of suspension compression (corner entry) and suspension roll (corner middle).
When your car is going perfectly straight, the giant sway bar is doing about zero. If the car is going straight and you smash the brakes then the ultra soft springs you have up there may not hold the car for a stable entry. You can fix the problem by adding stiffer springs for straight line (entry) braking, but then the middle may suffer due to the stiffer springs you thought you needed? From your baseline, adding front spring to get some help with corner entry stability coupled with moving Instant Center to the left creates a lever to help the car roll – now you get help under braking without suffering more spring rate during roll. The game is in balancing the Instant Center with the entry “dive” and the mid-corner “roll”.
Your car builder has the baseline figured out when it comes to Instant Center and Roll Center. But, track conditions change and driver styles vary. Maybe you can utilize Instant Center changes just like you use the Panhard bar? Try it and see if “Mikey likes it”.
The adjustment idea I like best for Instant Center manipulation is to use the same length A-Arm but simply move the upper frame pivot point up and down to get your desired result. I prefer moving the pivot point of the upper A-Arm for subtle adjustments. The benefit of moving the upper pivot point is that hardware is available to make it easy, you can make subtle changes, you avoid messing up the bump steer and the camber curves stay in line. Your car builder spent a mountain of time and testing on your baseline front end design so it pays to make adjustments that are subtle verses stretching the design parameters to extremes.
Using a slotted ear and slugs makes adjustments easy. You can move the pivot point in small increments by carrying a slug kit. You can raise and lower the Instant Center right at the track. If you want more roll, but don’t feel like you can run softer springs, you can simply change a slug and raise the RF A-Arm Pivot point. Raising the pivot point will move the RF Instant Center farther left and lower. The subtle adjustment gives you some turning help without decreasing braking stability. The RF gives you easy adjustment and you can “feel” the affect of the change just like when you move the panhard bar. You do have to readjust camber – easy deal.
Slugs that are marked give you an easy way to record Instant Center changes
Slugs that are marked give you an easy way to record Instant Center changes. A 1/4" slug makes a profound difference. Draw it out when you have time. At the track, just bolt in a pair!
A slotted A-Arm frame tab works perfectly with the slug system
A slotted A-Arm frame tab works perfectly with the slug system allowing for quick and precise adjustments.
The LF Instant Center is important too. You can use the LF to raise or lower the roll center. You can also use the LF to move the roll center left or right. You can accomplish the same thing with the RF, but this article is trying to provide simple examples to help your team see the concept and give you the confidence to try what may be a new adjustment for your team. You can certainly draw it all out, but for today just think about what happens when you move the Instant Center with simple A-Arm slugs.
When you run a Shorter RF A-Arm you generally move the roll center to the right. The shorter RF A-Arm has more angle and intersects with the lower control arm line faster – that is easy to understand, right? If the Roll Center is closer to the right it speeds the rate of travel and the car reacts quicker. Go too far and you will blast through the travel before the full force of the center of the corner arrives. When this situation occurs, the “soft push” is usually the result. So, this is a magazine article and you have a race car going around a real track. Reading is fun and accepting the limitations within this article will help you to just try adjustments. There are a ton of variables and the goal of this lesson is to simply discuss one element as if Instant Centers were not connected to anything else – of course they are! But, if by forgetting about all of the other “stuff” we can learn how to manipulate Instant Center adjustments to overcome a problem then we have learned something new.
An accurate billet caster camber gauge is a must
Changing A-Arm length requires the camber to be reset. A billet nut plate speeds changes when time is short. An accurate billet caster camber gauge is a must for any race team.
Since your car builder spent the time to build your car with a proven Roll Center location we want to be careful to not adjust so much that we erase the years of testing and knowledge that our car gives you when you buy a frame. So, from a prior article Roll Center is explained here:
Roll Center Explained
To simplify the Front Roll Center thought process it helps to understand the creation of the so called magical point. Front Roll Center is a calculated point verses a physical place. To find it you must first locate the Instant Center both left and right.
The RF Instant Center is found by drawing a line through the center of the RF upper A-Arm ball joint extended out though the center of the A-Arm inner pivot point on the frame. Another line is drawn from the RF lower outer ball joint center though the lower control arm frame pivot. The RF lower control arm line is extended out until it meets the RF upper control arm line. Where these lines intersect is called the Instant Center. The LF Instant Center is found in the same way.
After both Instant Centers are located you can now find the Roll Center. From the RF Instant Center you draw a line back to the RF contact patch center. From the LF Instant Center you draw a line back to the LF contact patch center. Where these two imaginary lines, running from the contact patches to the corresponding Instant Center intersect, is the Roll Center. Remember – the Roll Center moves as the suspension goes through travel.
Trial and error is still common
Spend time to learn about Roll Center when you are in the shop. At the track - trial and error is still common, even for Cup teams with full time engineers.Note:
Since the “Roll Center” location is a moving point is space it gets complicated – carrying graph paper at the track is not feasible, I prefer to spend time thinking about roll center during the design stage of building a chassis – and much thought is placed into Roll Center when designing any suspension.
At the track, it is easy to visualize Instant Centers and difficult to think out roll center. By simplifying, I can adjust Instant Center locations right at the track as I can easily see how the upper A-Arm line passes through the lower control arm line. With simple visual estimation, I can have another adjustment method at the track and I carry slugs to make repeatable changes just like I would move the Panhard bar or change a spring.
If you use a RF A-Arm frame mounting plate that is slotted for height adjustment you can use slugs to ensure you have repeatable and documentable changes. For the Front Instant Center adjustment you can simply record that you moved the RF inner A-arm mounting point up a1/8th inch with a slug. Changing a slug is pretty easy. If the driver doesn’t like the adjustment you can simply bolt the original slug back in.
Instant Center adjustments at the track can be used to create the feel of stiffer front springs under braking yet have the front springs feel softer in the center of the turn due to the longer lever that is created by the Instant Center length change. Many variables come into play and the teams that get the variables closest wins.
At the track – I usually focus on Instant Center adjustments by moving slugs on the upper A-Arms. You can move the lower points too, but you bring in rack location issues and bump steer corrections. The upper adjustment is easy to understand especially when track time is limited.
Lowering the RF A-Arm inner pivot raises the Front Roll Center and moves it to the right. Negative Camber is added and may need to be reset.
Raising the RF A-Arm inner pivot lowers the Front Roll Center and moves it to the left. Negative camber is reduced and may need to be reset.
Lowering the LF A-Arm inner pivot raises the Front Roll Center and moves it to the left. Positive camber is reduced and may need to be reset.
Raising the LF A-Arm inner pivot lowers the Front Roll Center and moves it to the right. Positive camber is added and may need to be reset.
The reality is that Front Roll Center is simply a derivative of the Instant Center locations. Instant Centers are simple even through dynamic roll. Why complicate your trackside thought process with imaginary lines? Keep it simple at the track and use slugs to maintain records and repeatability. You can engineer at will after the race and study the Roll Center changes you accomplished and measure the affects of bolting in a few simple slugs.
Engineering becomes more important in racing every day. When time is short, educated experimenting is equally as valuable.
- Download PDF joes_chassis_sheets__dirt_copy1.pdf