TrACkTICS: Dino’s 75/25 rule for braking on the track

Posted by Dino Crescentini

Any of you who read the recent “Science of Stopping” post from Steve Ruiz about the reality of balanced brakes probably got a bit of an eye-opener on the complex physics behind slowing down a vehicle. His insights focused on the effort that goes into the brakes long before the car ever hits the pavement.

Now imagine yourself behind the steering wheel at over 100mph barreling down on a sharp turn that is only a few dozen yards away. Throw another car right behind you and maybe another off to your side and you get an idea of what I face over a thousand times during the racing season as a driver for the Global Motorsports Group racing team in the SCCA SPEED World Challenge series. The concept of “balance” becomes very dynamic on the track.

Perhaps no skill is harder to execute perfectly on the track than slowing a race car at the limits of its braking performance. Braking changes the race car's weight distribution, posture, and handling characteristics. Do it right and you gain valuable time on the competition. Do it wrong and that podium finish gets farther and farther away. Do it really wrong and… well, you have probably seen the footage of what happens.

For a race car driver, most if not all of the braking happens in preparation for a turn. So not only is the vehicle’s balance shifting forward, it is also shifting side to side from the inside to the outside of the cornering direction. Even with the best equipment in this situation, each wheel is dealing with either too much weight for efficient braking or too little to optimally transfer the stopping power through the tires to the road.

So now what?

Probably the first lesson we learn, and one I would like to impart to you, is that the most efficient way to slow a car is in a straight line. This is when the car's weight is evenly distributed to both sides. The mission here is to complete as much of your braking as possible before commencing the turn.

When braking and turning at the same time, neither braking nor cornering occurs optimally, creating a true lose-lose situation. So getting as much of the braking underway as possible before the turn will pay dividends that can translate into victory.

This may create a bit of a disconnect for some of you. Cutting your velocity before the turn seems like a slow strategy in a speedy sport, but this is where having great brakes comes in. The shorter potential stopping distance of racing brakes and tires allows us to start braking much closer to the turn and still get our speed down to a manageable level before we need to move the steering wheel. Racers look to racing brakes for the ability to brake late so they can keep their hard earned momentum as long as possible.

Ideally all braking should be done before the wheel is turned for a corner. That’s easy when putting around a parking lot looking for a spot at the mall, but unrealistic in the heat of a race or time trial. However, on the track with the right car and equipment (I drive a StopTech-equipped but mostly stock Porsche for GMG) you should aim for my 75/25 rule. Essentially, you should realistically pull off about 75% of your deceleration before turning and cap off the last bit by the time you are 25% into the turn. That puts your vehicle into its best performance zone for three quarters of each turn. That is quite an edge.

The technique required is to very quickly get your brakes to the limit to start the deceleration, then ease back a little off the brake pedal as you start the turn until you are a quarter of the way into it.

It takes a knowledge of your car’s abilities and practice on a track, not a walled one in case you overshoot the turn. Watch the SCCA races on SPEED channel, which features production based race cars, and you’ll see the 75/25 rule being applied all over the place. Once you get it down, you will be glad you did.

Happy racing!

Dino Crescentini races for GMG Racing and is the CEO of Centric Parts, which includes the ultra-performance StopTech brand