Shocks are an important tuning tool that create feel in your car. With the variety of shock brands, components and types partnering up with a shock specialist can help you to navigate through the vast array of component offerings.
To increase our shock knowledge, we have interviewed two successful specialists in the shock field. Mike Naake of Naake Suspension Specialists and Mike Leary of Leary’s Shock Shop offer their suggestions and experience....read more »
Mono Tube COMP STROKE
Naake uses this photo to illustrate the base valve action on the mono tube compression stroke. As the shaft displaces the shock oil the base valve smoothly opens to allow for the shaft volume. Shim stacks can be seen flexing to meter the precise amount of shock oil.
Mono Tube REB STROKE
The Naake mono tube rebound stroke photo illustrates shock oil flow and you can see the internal forces and valving action. The mono tube gas separating piston is clearly shown at the top of the shock.
What is a Twin tube shock?
Many tracks and weekly racing series’ rules require a twin tube shock. They do this to keep the racers’ costs down. A twin tube shock has an inner tube that the piston runs in. At the bottom of the inner tube is a base valve. The function of the base-valve is to make 30%-40% of the compression force and replenish the oil in the inner tube on the rebound stroke. If a base valve is not performing with enough force in a twin tube shock that could result in cavitation or what we call in a twin tube design “dumping”. Dumping is when too much oil moves out of the inner tube too quickly and on the rebound stroke it is not replenished fast enough resulting in a momentary dead spot on the rebound stroke. The dumping can be verified on the rebound opening stroke of a constant velocity test on your shock dyno.
Twin Tube Comp
Naake uses this photo to show the low pressure gas filled bags utilized in twin tube shocks. The low pressure bags prevent foaming and deform to account for shaft displacement. The Base Valve adds 30 to 40% of the compression force.
Twin Tube REB STROKE
Naake points out twin tube shocks have an inner tube that the piston runs in. The twin tube rebound view shows the base valve metering oil from the outer oil reservoir.
Why run a base valve?
Base valves are of most benefit on heavy cars and when low gas pressure is used. For most late models we run without base valves in mono tube shocks to save cost. As you run high compression it can make sense to add a base valve to help prevent cavitation on the back side of the piston. When running a base valve the shock valving needs to be tuned to line up with the compression forces that are metered through the base valve.
A base valve is an optional component on a mono tube shock and works great with low pressure. Some series that allow mono tube shocks do not allow base valve to be installed. A base valve shock will have a much smoother feel to the driver than a non-base valve shock. Of course, a base valve in a shock adds to the cost. We are big fans of base valves when rules allow. The added control of the oil displaced by the shaft gives us more choices with our rebound adjustments as cavitation is eliminated through transition from compression to rebound.
Is shock oil important?
Leary & Naake:
Shock oil is a part of the shock that most racers overlook. Many manufactures use inexpensive hydraulic oil in their shocks. Inexpensive oil can vary through out the temperature range. You may start the race with a shock that has a 5 valving on compression and rebound. Inexpensive oil may react dramatically with heat and effectively make the 5 shock you built in the shop perform like a 3 shock on the track. Using thin synthetic oil reduces the viscosity change allowing for more consistent shock performance from ambient temperature to race temp.
Using a drip cup for shock rebuilding keeps the oil contained and your workplace clean. An organized shock building station is a must if you are servicing shocks on your own.
Leary tested several 5 shocks from different companies. This graph shows that a 5 shock valving varies significantly from brand to brand. Understanding the brand valving differences will help you to make the proper adjustments when using competing brands.
What Shock tips can you give to our readers?
We hear a common myth that bag shocks blow out due to rough track conditions or sudden high velocity compression. In my experience, I just do not see this at all. The only bag failures I have seen are due to errors in assembly or a bag had a small puncture prior to assembly.
You can perform a simple hand test of your twin tube style shock. Fully extend the shock. Position the shock so that the shaft end is up. Compress the shock about a half an inch. If you feel any slack or a dead spot, it is an indication of air in the system. This can be caused by the shock being low on oil, either from the shock having an oil leak or from not enough oil placed in the shock during assembly. It could also indicate a leaking gas bag. We perform this test on all twin tube shock prior to running a dyno test. If they don’t pass the hand test, they are guaranteed to fail the dyno test.
You should have your shocks dyno’d when they are new to get a baseline, and then should be re-dyno’d after a crash and halfway thru the season. A shaft bent 3 or 4 thousandths or a tiny dent in a mono tube shock body, will change the shock dramatically. In this day in age, it is almost impossible to build your own shocks without testing them on a quality dyno. Using the proper tools such as, shock wrench, shock vice and drip cup will make the building process easier and protect your investment. Keeping your shock work area clean and organized is pivotal to building successful shocks.
If you are going to work on your own shocks then using the proper tools such as a shock vice will help you to build winning shocks.
What shock adjustment tips can you suggest?
Most of the handling of a pavement car is controlled in the first 2 inches of shock movement. I like to use the rear shocks to control the entry of the corner, left side shocks and RF for the middle of the corner and the fronts for exit.
I avoid using the compression side of the shock for handling adjustment. I would rather use springs to control compression adjustments. The one exception is possibly the compression on the left rear – by increasing the compression at certain speeds, you can gain bite off the corner. It can make the car think is has more LR spring on exit without changing the corner entry like a spring can.
On a conventional spring setup, the shock settings will work differently than with a soft spring set-up. The more front spring rate, the less compression you need because the spring is doing the work. With a soft front spring set up, you need to use compression to control the speed of the front end movement because you have a 200 lb spring trying to hold up an 800 lb corner.
If you tie down the left rear shock on a conventional set-up, I’ve found you will tighten up the entry of the corner. I believe it keeps the left rear weight from transferring to the RR as fast, which gives you that loose entry feeling and keeps the weight on the LR tire.
With a soft spring set-up, if you tied down the LR, it usually will loosen the corner entry. Because of the rapid weight transfer to the RF of the car, we can overload the RF tire, which can cause a soft push on entry. By delaying that transfer the RF tire has a chance to “grip” the track, so the driver feels the car is looser on entry.
With either conventional or the soft spring set up, the rebound on the RF can help that “tight in the middle” feeling. By stiffening the rebound on the RF it holds weight on that tire and helps it maintain grip – it also keeps the RF from transferring weight to the LR as fast, which will cause the car to pick up a push. The downside of holding down the RF is you can lose some grip off the corner, because you are delaying that weight transfer to the LR.
When we have soft front springs, we need the rebound on the LF shock to help the sway bar to keep all that weight transfer to the RF. That is why we see the extreme tie-down LF shocks. It is important to balance your front springs/sway bar and tie-down in the LR shock. We build LF shocks at 1 inch of travel anywhere from 600 lbs of force to 1000 lbs, depending on the set up.
Changing the sweeps on externally adjustable shocks makes a big change. Leary uses this dyno graph to illustrate the dramatic effect of using sweep adjustments.
To help free up the car from the center off a quick adjustment is to add gas pressure to the RR shock. By adding up to 200lbs (if you have the right hardware) the car can take on a better attitude and become more stable on exit. This fix is quick and can be removed quickly if the driver is still looking for a better exit.
With today’s set ups we like to maintain rebound in the front shocks. If the car is tight, and if the team has the right hardware, we try to go with high frequency pistons to relieve the tight feeling. In short, there is an o-ring behind the shaft band that delays the metering of oil through the bleed holes for a brief moment and then shuts the bleeds off just as quickly. Our teams can work with us to discuss these options to find more speed – our goal here is to let your readers know that there is high tech hardware out there that goes beyond generic answers. We have proven results in gaining front grip off the corner with the high frequency hardware available. Remote canisters provide another layer of adjustability when allowed.
While high tech is cool sometimes a basic answer works well. If your car is tight then more compression in the RR will help the car turn in the center. You can try a bit more rebound in the LR to free it up. You can take a little compression out of the LF or tie down the RF to help the car turn. Extreme rebound in the front shocks is good in many cases but too much low speed control can reduce front grip. With extreme front rebound you need some bleed to allow the tire to follow the track surface.
When rules allow a remote shock canister gives you more compression adjustability options. Base valves can be built into remote reservoirs and the housing needs to be protected from damage. Using a canister mount allows for quick adjustments when practice time runs short.
Shock science and hardware is constantly changing and the application of the set up tips is very dependant on the track, driver and location in the turn. Many times a standard shock tip will change 180 degrees based on moving the car a few feet in the corner and the tips above need to be applied with full understanding of shock mechanics – both Mike’s will change their adjustments based on real world data. When it comes to shocks it is all about timing and transitions. Shocks might hold or delay movements but in the end the springs carry the load. Bumps, braking, throttle and rolling through the middle all provide information that will be analyzed independently by your shock guru. Be aware that you may have soft front springs but you also must consider the overall front spring rate based on the giant sway bar that could be in your car.