Today I was looking back at some old YSAR posts and thought it was time to revisit some of my favorite posts and add a little commentary. “Tossing the nannies” is one of my favorites because it’s about braking. Braking is an incredibly important skill. I’d say it’s the most critical skill there is in driving because the brakes are used for turning as well as scrubbing speed. Most cars come from the factory with safe brakes, but when racers start mucking about with pads, prop valves, and ABS-delete, things can go poorly.
Most cars have enough brake power to lock their wheels. So your stopping distance is generally a function of the tires and road surface, not the brake pads and rotors (but of course these matter because of heat and feel). One aspect of braking that is often overlooked is brake bias. When you step on the brake pedal, some of the brake pressure goes to the front, and some to the rear. But it’s not the same amount. As the car slows, weight transfers from the rear to the front. The front tires gain load and therefore gain grip. Not only does it make sense to bias the brake pressure towards the front to take advantage of the added friction up there, it’s also a lot safer. If the rear tires lock up first, it can lead to a spin. Like this.
Why did this car spin while decelerating in a straight line on a dry track? The short answer is that real racers toss the nannies. No self-respecting racecar driver chooses an automatic transmission. It’s a stick or stay home. Real racers do their own throttle blipping too. Traction control? And lose the ability to do burn-outs? Surely you jest. Power steering? For weaklings. Stability control? Might as well have gramps drive for you. Anti-lock brakes? Everyone knows that threshold braking requires the tires to slip and ABS doesn’t allow that. Real racers turn off or permanently delete the nannies.
This racing team acted on their correct understanding that on a wet track, the overall traction is lower, so the weight transfer from rear to front is less pronounced. You can stop in a shorter distance on a slick track with more rear brake. So they adjusted the bias towards the rear. Nothing wrong with that, it’s what the pros do. But then the track dried, they didn’t readjust the bias, the driver locked the brakes, and the car was wrecked (which is not what the pros do).
There are several ways to deal with this situation.
- Don’t mess with the brake bias. It comes from the factory with a lot of front bias. Brake a lot earlier on a wet track.
- Pit the car when the track conditions change and make the necessary adjustments.
- Make the brake bias adjustable from the cockpit (this assumes the driver knows when and how much to adjust).
- Keep the ABS nanny. What you lose in braking distance you make up for in safety.
Going from a wet track to a dry track isn’t the only time you may experience too much rear brake. Racing tires have more grip than street tires, so they transfer more load to the front. When you swap your street tires for R-comps, you probably want to reduce the braking in the rear. If you don’t have a prop valve, you can put a more aggressive brake pad on the front than the rear.