Tuning With Brakes

Brake problems cause more handling problems than most racers will ever know or admit. These two stories are real accounts that happened to real racers.

Our first case is related to us by Dan Press of Dan Press Industries. Dan has many years of driving and crew chief experience in addition to his knowledge of the manufacture of racing parts. He has raced against and helped some of the leading drivers in NASCAR's top series. He tells of one testing session with a two-time NASCAR series champion.

"It makes no difference how much experience you have," Press relates. "You can miss this. I was standing in the flagstand watching the car go into the corner. The driver came in and said, 'It is pushing in the middle'. I said, 'No way, that thing is loose getting in. I can see your hands straight up on the steering wheel. You never even turned to get into the corner.' He said, 'No, it wasn't. I can't get it to stay down in the middle of the corner.' I told him to put two turns of front brake in it, go out, and try it. He went out and said, 'Now it is loose in the middle of the corner'.

"What happened was that he got rid of the initial brake-induced loose entry. He could now hit the mark getting into the corner and the car stayed down. The car was actually loose in the middle, not pushing."

Press continues, "There is an experienced driver and he did not realize he had a brake problem. If he didn't fix the brakes, he would have been working on trying to get the push out of the middle of the corner. All he would have done is make the loose entry worse. Probably a good 30 percent of brake problems is a result of not having the brake system balanced out."

Carl Bush at Wilwood Racing Products tells our other story. "We did a test last year at Martinsville with a top-10 Winston Cup team. They got the car to the point where the driver was very happy with the overall balance of the car, including the feel of the brakes. They were clicking off some pretty good lap times.

"While the driver wasn't looking, the crew chief made a change in the brake pad compound. That was the only change made. It didn't take very long for the driver to come on the radio and say, 'I don't know what you did to this car but this thing is pushing like a son of a gun. Change it back to where it was!'

"The driver had no clue if the crew chief changed a spring, a shock, a sway bar, tire pressures, or weight percentages. He only felt the car was now pushing getting in. It did not feel like it was slowing down as well.

"He brought the car back in. While the driver was away, they put on new pads with the old compound. The driver went out, was clicking off laps again, and now he was a happy camper and ready to go qualify."

Bush goes on to explain, "The difference in the pads was the torque ranges. The driver was happier with the higher torque pad. It had more stopping value for the same amount of pedal effort. When we went to a lower torque pad, he was on the brakes but it didn't feel like the car was slowing down. He did not change his braking point. Therefore, with less torque, the car was running into the corner deeper, harder, and a little more out of control than when the car slowed down quicker and settled down on the bottom better. He was trying to turn in and carrying too much speed, so it pushed up the track. Drivers feel the car is pushing so they want to change springs and shocks, where making a brake change will solve their handling problem."

How do you recognize a brake-induced problem as opposed to an incorrect chassis setup? Press explains, "There are several ways to go about it. You have to train yourself to recognize certain problems. What usually happens is a driver will say, 'I don't think there is a brake problem because I went in without using the brakes and the problem still exists.' What he must understand is he is not entering the corner the same way. He had to let off early and coast into the corner or he lifted at the same point and carried too much speed and overshot the middle of the corner. Not using the brakes doesn't mean he doesn't have a brake problem.

"If you are adjusting on the car and making drastic changes and you don't see the car change, nine times out of ten, it really is a brake problem. "Usually the problem is going to be a loose entry problem. One good way to notice what is going on is to put a piece of tape on the top of the steering wheel. Pay attention to where it is when you enter the corner. If you see the tape straight up or back to the right of center before you get into the corner, it is a pretty good indication that the car is getting loose on entry. You are just trying to correct it.

Press continues, "I'm not talking about being so loose to where the thing is backing into the corner. When this happens, he misses the turn-in point getting into the corner and the car is tight in the middle. This happens because he couldn't turn it all the way in because he was holding the steering wheel straight to get the looseness out of it. When he did turn in, it was a little too late. If you miss the mark by a foot on the initial entry, you will be off five feet in the center of the corner. That is the most obvious problem."

If you are making spring, shock, or suspension setup changes and, no matter what you do, the car still has an entry problem, there is a brake imbalance. In general, there are two brake-induced handling situations a racer needs to understand, so he can use them to his advantage.

A car that has too much rear brake will have a tendency to get loose or oversteer on corner entry. A car that has too much front brake bias will have a tendency to push or understeer. The driver can use this knowledge to win races because, as the race unfolds, things change. If you have your brake system balanced at the beginning of the race, you can tune the car with the brakes during the race to overcome changes and make your car faster.

The ability to make changes during the race requires having a balanced system back in the garage. You must understand how each component works independently and how it affects the system's ability to work together in making the car stop as quickly as possible.

Stopping begins when the driver steps on the brake pedal. The driver's muscle power is multiplied by length of the pedal. Different length pedals offer different ratios, giving different mechanical leverage on the master cylinder.

The master cylinder converts the leverage into hydraulic line pressure that is sent to the caliper. There are different size master cylinders to deliver differing amounts of hydraulic pressure. That pressure is multiplied by the effective square inches of piston area in the caliper. Different size calipers have different amounts of piston area to balance the clamping force on the rotor. The larger the piston area, the more clamping force is exerted on the rotor by the brake pad.

As we have seen, brake pads have various torque values to slow the car. The pads squeeze the rotor, which acts as a lever. The larger the rotor, the more force is able to convert the car's kinetic energy into heat energy and stop the car. That is a brief explanation of how the multiple components of the brake system all work together to stop the car.

The place to start your quest for a balanced braking system is with the pedal's balance bar. Press explains, "The biggest thing we stress when setting up the brakes is you want to make sure the balance bar is sitting square, when you have a hard pedal. The static setting for the front master cylinder rod is going to be about 3/8 inch longer than the rear master cylinder rod. When you push on it and have a firm pedal, the balance bar should be square. That is the most critical part of setting up your brakes. If you don't have that right, I don't care what size master cylinder or calipers you have on it, you are going to have a problem. There is only so far the balance bar can move before it binds itself up.

"The biggest things I see people doing wrong from a tuning standpoint is an incorrect front-to-rear balance and how much braking is being done with the front of the car.

"Starting with the master cylinder sizes, usually you see guys running a one-size difference. You will see a 7/8-inch on the front and 1 inch on the rear. I like to see two equal sizes. Some guys have gone down to 3/4-inch in the front. I don't like getting too small on the front master cylinder because it gives you a sponge pedal later in the race.

"If you don't want to change the master cylinder size and stayed with the 7/8-inch/1 inch, you will be one or two turns from being all the way to the front on the pedal balance bar. By changing the caliper sizes, we have been able to make that six or seven turns from the front, so you are closer to the middle of your balance bar. That gives you some room to move."

Press explains his new thinking on balanced caliper sizes. "We used to match front calipers that had 2-inch pistons with calipers that had a piston size of 11/2 inch in the rear. Some guys used 13/4 inch for the front and 13/8 inch for the rear. That has been the standard sizing from the middle '80s through the mid-'90s. In order to balance the whole system, we are now using front calipers with 17/8 inch and 13/4-inch split pistons. In the back, 11/2 inch is probably the largest we use. Most of the time now, it is 11/4-inch piston size in the back. In square inches, that is quite a bit of difference. With 11/2 inch pistons, that is 31/2 square inches of piston area on one side of the caliper. With the 11/4-inch pistons, you are down to 21/2 square inches per caliper. That smaller size caliper seems to match up better with most asphalt Late Models, and makes the system more balanced.

"We have done the same thing with the GM calipers. They now have a 23/4-inch single piston up front and a 23/8-inch in the back. Everybody used to run 215/16-inch all the way around.

"For dirt cars, they are running either the same size caliper all the way around like a 13/4 inch or they run three 13/4 inch and on the right front a 11/2 inch."

Bush goes on to make some comments about the effect of the rotors on caliper sizing and the brake system overall. "With the speeds these guys are reaching, especially on the fast tracks, and with the lower compression engines not slowing the cars down as much, they are relying more on the brakes. We are seeing guys using 123/16-inch rotors. Consequently, the car now feels the higher brake torque because of the leverage of the larger diameter front rotors.

"The real reason to go to the larger [front] rotors is to help compensate for the increased heat. An additional benefit to the larger rotor is it has more torque against the wheel to slow the car down. Now, we are seeing guys in an effort to bring themselves into a proportionate range of balance still using the smaller 113/4-inch rotor on the rear of the car because it is adequate to handle the heat being generated back there. So they can let the piston size creep back up a little bit on the rear caliper to keep the same front-to-rear balance based on the fact that the front rotors are now a little bit bigger."

Press points out a mistake made by racers. "You have to have really good rotors on the front of an asphalt car. On the back, you can get away with something that is lightweight because you are doing minimal braking with the rear brakes. I see people trying to go lighter and lighter on the front braking system. For the most part, you need a stout caliper that is very rigid in the front.

"The guy runs 5 to 10 laps in hot lapping the car and it is working well. Then, in the heat of battle, trying to pass people, running hard lap after lap, the whole scenario changes. You are running behind cars and not getting a lot of air to the brakes. You have to run the car really hard up into the corner trying to stay on the guy in front of you, without running over him. All of that is what makes your car need the best brakes you can get on it. In a 50-lap race, lightweight brakes go away. Racers need to stop looking at the one lap that is getting them in the race and look at what they are up against the whole race."

A rotor performs two functions. Its primary function is to absorb and then dissipate the heat caused by the friction of the pad. The second function of the rotor is to act as a lever to slow the car.

Press makes some very important points about setting up the initial brake balance. "You need to use a pressure gauge. A good starting spot on asphalt is when the front gauge says you have 500 pounds and the back one is between 275 and 300 pounds. This will work unless you have a big mismatch in caliper sizes.

"You should be within one or two turns on your balance bar from being right if you use the gauges. I use the screw-in gauges because I can take them out. If you run in-dash gauges, you definitely want to run shut-off valves. The gauges are like a spring or sponge. When you push on the pedal, it will make the pedal spongy."

Bush passed on some closing thoughts on a balanced brake system. "It is very easy for guys to start relying on brakes and brakes only to change the way their car gets into the corner. A racer needs to understand if he has the brakes adjusted all the way to one end of the race car--to make the car either remain tight or allow it to initiate the turn--he is going to use those parts up a lot quicker, as opposed to the car being in a more balanced situation. If I found myself compensating every week with lots of rear brake to make sure my car was loose enough or free enough to initiate the turn in, I would go back and work on my car's setup. The racer should use the dynamics of the chassis as opposed to relying on the brakes to make his car perform.

"Ultimately, we are looking for the perfect balance of slowing the car down and having maximum grip on all four wheels and having the car settle down square. That way, as soon as the car is in the corner, you can get back into the throttle sooner. The faster you are on the throttle, the faster you are going to come off the corner. Racers should not use the brake system as a crutch to make their car turn or make it stop pushing. They need to understand how to adjust it so it gives them that balance."