Make or Brake
When I was helping my Dad work on racecars, at the age of 12, he taught me that 4 tires work better than 3 for the best corner speed. The same thought applies to braking – 4 tires work better than 2. Ensuring that your brake system is set up properly will gain you speed throughout the race. Teams that spend the time and think out the variables will beat their competition by out working them and the cost is generally effort over big dollars. Getting the most from...read more »
Brake Balance Bar Setup
Image 1 - Feeding your brake system with cool air will help your components last and make your car faster at the same time. For this application a single hose gets the job done, but two hoses are often a good idea. The odds are stacked in your favor if you spend the time to saturate your brake components with plenty of cool fresh air.
A proper brake balance bar set is a simple place to start. Following the manufactures brake balance bar set up sheet will prevent many problems. Often I have seen brake balance bars that allow the rear master cylinder to engage before the front. When this occurs the car will be unstable on corner entry and regardless of how much front brake you dial in the car simply will not be fun to drive. Read the manufactures brake balance instructions thoroughly. You can check your car easily as the brake balance bar should be perpendicular to the frame when the brake pedal is depressed. If your balance bar is perpendicular to the frame at zero brake pressure then it is likely that the rear brakes will engage first. Whenever the rear brakes engage first you can bet handling problems that are impossible to overcome will follow.
Another common brake balance bar set up problem is proper clearance at the clevis. Refer to your manufactures instructions but in the end the master cylinder rods should be parallel and the components should have enough clearance to prevent binding throughout the brake balance adjustment range and through full pedal motion. Without proper clearance the brake balance adjuster can bind up during the race at full rear or full front bias making for a tough night.
Driving Style Adjustment
Drivers play a role in maximizing rear braking as well. Brake smashers will require more front brake bias whereas smooth braking drivers can run more rear brake. By spacing out the time between lifting off the throttle, rolling in, and then applying smooth braking pressure provides the opportunity for teams to get more from their rear brakes. Smooth drivers that are easier on tires often get the most from their brakes.
Selecting the right friction material on your pads will help you with your goal of running more rear brake. Heavy brake users almost always end up with harder pads on the front whereas smooth drivers can use softer front pads. Finding the right combination for your car, driver and brake system can be a trial and error process. You can speed the process by working with your pad manufacturer or the parts supplier at your track. Typically, your parts supplier will know what competing teams are purchasing. Your team can tailor choices based on the appropriate variables and your crew usually knows if your driver relies on heavy brake pressure. If you build your system right you can win races with a heavy braker or with a smooth driver. If you have a brake smasher encourage using less brake pressure but remember that it is hard to change a driving style.
Weight vs. Stress
Rotor and caliper size comes into play – if you run lightweight components you will build brake temperature very quickly and can over-stress undersized parts. Initial stopping force may seem fine but if you go through center on the heat range then the components become too hot and the heat is not dissipated properly due to the lack of mass. Warping and glazed pads are common results when under sizing brake components. When the heat induced brake fade occurs, the result is a natural adjustment of adding more front brake bias. For short tracks I would always choose the extra weight associated with a good brake system verses compromising braking efficiency and longevity. The weight savings offered by brake components that are too light is not worth the negative results.
Proper Brake Ducting
Proper brake ducting is a must. For short tracks I would worry less about aerodynamics and drag and focus on keeping the brakes fed with plenty of fresh cool air.
Locating your brake ducts towards the center of the nose will feed your brakes with the most air. As you move towards the outside of the nose the air moves around the car and not through your brake ducts. Mounting the brake ducts as close to the radiator opening pulls in the most air.
Image 2 - Pulling air from the center of the nose as close to the radiator opening as possible improves airflow to your brake system. If you place your ducts too close to the edge of the nose air goes around the car instead of through your duct work. Keeping your brake system cool is a priority over the minimal negative aerodynamic effects. For short tracks good brakes prevail over any aero advantage.
In line fans are an efficient and inexpensive way to keep your brakes cool. For short tracks fans are a must. They are lightweight and with a flip of a switch they can be turned off if needed.
Rear brake ducting is not always needed but I think it is a good idea. Fresh air to both the front and rear brakes helps the components last longer and can prevent seal damage, fluid boiling and pad glazing. As we focus more on rear braking power then proper ducting comes into play.
Adjusting your car with a brake balance adjuster during the race can be your ticket to victory lane. When you have a tight car dialing in more rear brake can be an easy cure. A loose entry is often fixed with a few turns to the front. Selecting a brake balance adjuster that has an easy to reach handle helps drivers to make bias changes under race pressure. Adjusters with ball detents ensure that the bias adjustment stays put and the detents assist in monitoring the front to rear bias setting.
Image 3 - Using a brake balance adjuster system with an easy to reach handle and ball detents helps drivers to maintain the desired brake bias setting under race pressure. This model has heavy duty flexible connection hardware that eliminates binds at the balance bar. The lightweight construction bolts to your car fully assembled due to the mounting hole layout. Be sure to check your manufacturer's instructions for the proper brake balance installation. Note: There is now a 12" Hard Line, 60" Flex Cable package available to retrofit your Brake Balance Adjuster.
Choosing high quality fluid in the smallest containers possible is another critical braking rule. As soon as a bottle of fluid is opened it begins to deteriorate. Moisture in the air reduces the boiling point nearly instantly so it is a good idea to use only new bottles when filling your system and toss out partial bottles right away. Once opened – brake fluid will never be as good as a fresh bottle.
Bedding brakes is an often overlooked area. Rotor bedding and pad bedding are to separate processes. Be sure to clean new rotors removing any oils or foreign materials. Rotors need to be brought up to operating temperature slowly and then returned naturally to ambient temperature.
When bedding rotors I recommend taping off most of the duct work and ask the driver to bring the brakes up to temp with several stops. A few stops at easy pressure and then several at medium pressure. Just simple brake stops without being overly aggressive. Upon returning to the pits I get the car on stands and rotate the wheels every few minutes to prevent the pads from sitting in the same rotor spot during the cooling period for even heat dissipation. Proper rotor bedding will provide for longer lasting rotors and reduces the chance of heat cracking. Once the rotors have cooled completely your driver is ready to use the brakes at their discretion.
For pad bedding follow the manufactures instructions but be aware it is a needed step. Bedding pads properly cures the pads and preps them for race conditions. Bedding improves stopping power and prevents pad failures. When bedding pads on used rotors, be sure to remove the existing pad material off of your used rotors. This is especially true when changing pad compounds. A vibrating or DA type sander with medium grit sand paper will work fine. Cleaning off the existing pad material from used rotors allows your new pad material to mate to the rotor for consistent performance.
With a few minutes of time you can improve lap times by helping your car to stop efficiently. Using all four tires to get your car deep into the turns is much better than using just the front 2. By spending the time to set up your brake system correctly, you can use effort verses money to gain long lasting speed. Stop and take the time to use the braking action to help your car go.
Master Cylinder Math
Going faster creates a need for stopping faster. Efficient braking is based on choosing the right components and matching the proper combinations will result in a brake system that works in conjunction with the specifics of your car, track and driver style. It is highly recommended that you work with your brake company engineer to assist you in building the right combination to tailor a system for your application. Since pad compound, rotors, calipers and...read more »
Billet Clamp on Reservoir Mount
A Billet Clamp On Reservoir Mount allows you to mount your brake fluid reservoir at a high point resulting in improved brake bleeding. Remote mounting keeps unwanted heat away from your brake fluid.
Q: How do you pick the proper master cylinder?
Master cylinders are an integral component in the brake system. They are responsible for sending the correct amount of pressure and balance to the brake calipers. But it must be remembered that they are only one component in a system, and do not function alone. Brake requirements for different types of race cars will vary by component and element. But all systems do carry a common thread. They must allow the driver to stop the car with comfortable leg effort while contributing to the overall handling and performance of the car.
Q: How do master cylinders work?
A master cylinder is used to convert force from the brake pedal into the hydraulic pressure that operates the brake calipers. The amount of pressure generated is a function of the force being applied, divided by the master cylinder bore area. A 1” master cylinder has a bore area of .785” inches squared. For every hundred pounds of force applied to the master cylinder piston by the pedal pushrod or balance bar, that master cylinder will generate pressure equal to 100 divided by .785 or 127.4 PSI. By calculating the area in inches squared (bore x bore x .785”) for any master cylinder size, you can calculate how much pressure change would be affected by a bore size change.
A 7/8” bore master cylinder has a bore area of .6” inches squared. If we apply that same 100 pounds of force to the 7/8” master cylinder, using the formula 100 divided by .6, that same 100 pounds of force from the pedal will generate 166.7 PSI. A decrease in master cylinder bore area produced a proportionate increase in line pressure. This line pressure management becomes a key factor in setting brake balance.
Master Cylinder bore size
Master Cylinder bore size is the element that affects pressure
Carl explains that a 1” Master Cylinder has a bore area of .785” squared. To get to this number you use the formula for Area which is: Area = 3.14 (Pi) multiplied by the radius squared. So you calculate the radius of 1” bore which is simply half of the diameter which equals .5” (half an inch). The result is that a 1” master cylinder has a radius of half an inch. You then multiply your radius which is a half an inch (.5) by itself so .5” X .5” = .25” or a quarter of an inch. .Multiply .25 X 3.14 (pi) and you arrive at Carl’s .785” area number. Basically, I just repeated what Carl said in an effort to make the math more simple and I bet the barrage of numbers made the calculation more intimidating and confusing? It’s ok – we will get to a simple way to look at the master cylinder math and going through the steps will make the process easier to understand.
Another way to explain Carl’s math uses a 7/8” master cylinder as the example. We will do the calculation and show our work to reinforce the math for calculating bore area.
Bore = 7/8”
7 divided by 8 gets us the decimal equivalent = .875”
The Radius is .875” divided by 2 = .4375”
.4375” Multiplied by .4375” (Squared) = .1914”
.1914” Multiplied by (Pi) 3.14” = .6” - which is the answer Carl explained above.
With the progression towards understanding the math we can do take the steps the easy way. Use Carl’s magic formula of Bore X Bore X .785” (.785 is the magic number that simplifies the above equations as it simply pre-calculates the squared business relating to Pi in advance). So a 7/8” bore is .875” X .875” X .785” = .6” Bore Area. It turns out you can use the number .785” and multiply it by ANY Bore X Bore as the reusable number of.785” is a derivative of Pi and it is a repeatable math number that can be used with any and all bore sizes. So, the complicated math shown relating to Master Cylinder Bore Area can be simplified. Now we have taken another step towards understanding.
Bore X Bore X .785” - you can always use .785” in the equation.
Let’s check with the Easy 1, 2, 3 method:
For an example 7/8” Bore master cylinder the Bore Area math is:
Step 1 – Convert the fraction Bore to a decimal by dividing the bottom number in the fraction into the top number.
- 7 divided by 8 = .875”. 7/8” is the bore marked on the outside of the master cylinder and .875” is the decimal bore equivalent of 7/8”
Step 2 – Multiply the bore diameter (our example is .875”) by itself which is the same as bore squared.
- .875” X .875” = .766”
Step 3 – Multiply the bore squared result from step 2 (.766) by the reusable number (always .785 with every master cylinder size – you can count on .785 to work every time with every master cylinder size).
- .875” X .875” = .766
- .766 X .785” = .6
- .6 is the Bore Area for a 7/8” Master Cylinder!
- The EASY 1, 2, 3 Bore Area calculation is right here!
Our example was for a 7/8” master cylinder. Now you can use the bore size on your car and substitute your actual numbers to come up with your Bore Area, front and rear, by following the 1,2,3 calculation above. Now that we have our Bore area numbers of .6 for a 7/8” master cylinder and .785” for a 1” master cylinder what do we do next? Carl states that a smaller master cylinder bore creates more pressure with an equal amount of force. A 1” master cylinder creates 127.4 PSI as compared to a 7/8” master cylinder which is 166.7 PSI based on your foot making 100 pounds of force at the master cylinder. It is important to consider that the smaller cylinder makes more pressure but the smaller bore will move less fluid. More travel will be needed to make up for the reduction in fluid moved by a 7/8” master cylinder as compared to the larger 1”. Carl explains further in the next section.
- Step 1 – Convert the fraction Bore to a decimal by dividing the bottom number in the fraction into the top number.
Utilizing a bolt on caliper mount ensures that your calipers are square to the rotor improving pad wear and braking efficiency.
How do fluid volume and leverage come into play?
While a change in master cylinder bore size affects a pressure change, it also changes the amount of pedal travel realized to add the additional stroke needed to displace enough fluid to move the caliper pistons. This volume ratio plays an important role in the clamping capability of the caliper, and leverage that the driver has to generate that clamping force. The ratio between the caliper and master cylinder is a function of the net effective caliper piston bore area divided by the bore area of the master cylinder. To compare these ratios and do the calculation, you must start with the total piston area of the pistons in one side of one caliper.
A front brake set using four piston calipers with 1.75” diameters will have a net bore area of 4.8” inches squared as each 1.75” diameter piston has an individual bore area of 2.4” inches squared.
Jeff’s Easy Math works for caliper piston bores too – 1.75” X 1.75” = 3.06” X Reusable Number .785” = 2.40” X 2 Pistons = Carl’s Net Bore Area of 4.8”
Carl Bush - Continued
By running the formula, the leverage ratio between a 7/8” bore master cylinder and the 1.75” four piston caliper will be equal to:
Effective Caliper Piston Area (4.8) / Master Cylinder Bore Area (7/8 which is .6) =
4.8 / .6 = 8 for an 8:1 ratio
The driver leverage is then determined by multiplying the Pedal Ratio x the Caliper Piston Bore to Master Cylinder ratio. (Note from Jeff: “The pedal ratio is marked on your pedal assembly when you buy it or use the Pedal Ratio Drawing shown”)
Pedal Ratio (6:1) x (Piston Bore (4.8) / Master Cylinder Ratio (.6) results in (8) = Driver Leverage (48:1)
6 x (4.8 / .6) = 48:1
You can substitute any number of piston bore combinations with master cylinder sizes with any pedal ratio to determine the driver’s actual brake leverage.
For fun Carl has given you the answer to the test with this chart.
Common Caliper Piston Size Diameter / Area
Diameter, Inches 1.12 1.25 1.38 1.62 1.75 1.88 2.00 2.38 2.75 2.94 Area / Piston, Inches 0.99 1.23 1.48 2.07 2.40 2.76 3.14 4.45 5.94 6.78
Common Master Cylinder Bore Sizes / Area
Diameter, Inches 0.62 0.75 0.81 0.88 1.00 1.12 Area / Piston, Inches Sq. 0.31 0.44 0.52 0.60 0.79 0.99
By changing to a 7:1 ratio pedal (from the 6:1 shown in Carl’s Example), the driver would then realize a final ratio of 56:1 with the same caliper and master cylinder (Jeff’s math 7 x (4.8 / .6) = 56:1). Consequently, a 5:1 pedal would only give the driver a 30:1 ratio (Jeff’s math 5 x (4.8 / .6) = 30:1). If we compare the front leverage ratio to the rear leverage ratio on any given car, this tells us the front to rear static bias capability of the car.
A = Distance from pivot point to middle of push / pull point
B = Distance from pivot to point of push on master cylinder
P = Pivot point
F = Force or push
Pedal Ratio is determined by dividing length "A" by length "B". The amount of force at "F" determines the force to the master cylinders
Now that we know the math, can you explain a common set up for our readers?
A common set up that could be found on a weekly show short track asphalt car is to use the example above with 1.75” piston calipers on the front with a 7/8” bore master cylinder, and a pair of 1.38” piston calipers on the rear with a 1” master cylinder. A 6:1 floor mount pedal ratio is also common. We have already determined that the 1.75 pistons with a 7/8” master cylinder and a 6:1 pedal will give the driver an overall brake leverage of 48:1 on the front. If we use the same formulas with the 1 3/8” piston calipers and 1” master cylinder on the rear, that produces a total driver’s rear leverage ratio of 22.75:1. When we compare the 48:1 ratio in the front, to the 22.75:1 ratio in the rear, we see that the car will be baselined with a front to rear static leverage bias of 67.8%, as long as the balance bar is centered and equal force is being applied to both master cylinders. You can substitute any combination of parts and their sizes to determine the exact influence they will have on the baseline static bias ratio.
- Four piston calipers Four piston calipers can usually be found with piston sizes from 1.125" to 1.875". The area of two pistons on one side of the caliper determine the calipers influence on clamping capability.
How do we use pressure to determine brake bias?
Although racing with a perfectly centered balance bar is the ideal goal, it seldom happens in reality. Besides, one of the advantages in using an adjustable balance bar is having the ability to adjust that leverage to optimize handling and driver comfort on track. Trying to measure the post-race leverage split at the balance bar is difficult and unrealistic. However, using pressure gauges to measure pressure differentials s at any given balance bar setting is relatively simple. The brake gauges will show the actual pressure split in the car based on the balance bar adjustments made by the driver. Those pressures can then be multiplied by the effective caliper piston bore areas to calculate the last on-track static bias settings.
Going back to our (common setup) example, if we apply 50 pounds of leg force against a 6:1 pedal, we will generate 300 total pounds of force against the balance bar. If the balance bar is perfectly centered, it will distribute that force equally to each master cylinder. With each master cylinder receiving an equal force amount of 150 pounds, the 7/8” master cylinder should produce 250 PSI (Jeff’s math: 250 PSI comes from 150 divided by .6 which is the 7/8” master cylinder math result) while the rear 1” master cylinder produces 192 PSI (Jeff’s math: 192 PSI comes from 150 divided by .785 which is the 1” master cylinder math result). In practical use of gauges, you can use any level of effort and pressure for your comparisons. The end result will be the same.
When the front pressure of 250 PSI from the 7/8” master cylinder is multiplied by the 4.8” inches of caliper bore area of the front 1.75” piston front calipers, we get a front clamping force of 1200. On the rear, we will have 192 PSI x 2.97” caliper area or 570 pounds of rear caliper clamping force. When comparing the these front to rear clamping force total in the same way you would compare wheel weights for balance, we would see that this car has a total of 1770 pounds of caliper clamping force at these line pressures with 1200 pounds or 67.8 % on the front. It’s that same static bias ratio that was measured using the overall driver leverage ratios.
Now, if every car and driver had the same braking requirements and pedal feel preferences, we would never need to adjust anything. But, every car and every driver are unique and adjustments will get made.
The ratio examples that have been used here are very common in many short track asphalt cars. But your car, for a wide variety of reasons, may have quite different requirements. As a racer or crew chief, you can use these formulas to map the existing brake setup on your own race car, and then make calculated decisions when the desired handling or driver feel isn’t being delivered. The inability to reach the desired bias or driver’s feel of the pedal is the indication you will need to evaluate your component selection and consider possible alternatives. By using the formulas in these examples, you can accurately calculate what affects a component change will make to your existing baseline, and record those final ratios in your records to use for future adjustments and set up for any given track type or conditions.
- Metric Caliper Calipers such as this metric replacement only have one piston on one side. The calculation of their clamping capability still uses the same formula.
- Closing As you can see, using the experience of you brake manufacturer is very valuable. Still, when you breakdown the math it is not all that hard. By understanding the pressures, bore areas and ratios you can improve your understanding of the brake system. A thorough understanding will help you to make improvements to an existing car or transfer learned knowledge to a new car. Be taking the time to understand the basic math behind the braking system you can calculate and record winning brake set ups. Slowing down to do the math will help you to go fast.
IMPORTANT NOTE: This particular user installed the rotor the wrong direction which can cause it to “Cam out” and rub on the inside of the caliper. Be sure to mount your rotor for the correct rotation.