Hitting Apexes…. Nov 2014

Hi Gang. Our season is winding down and planning for our 2015 season is under way. In the September P4Us I wrote about passing because of some issues we have witnessed at a recent track event. In the October P4Us I figured I would try to touch more on the basics of HPDE driving and wrote about learning the line. In line with that, this month I will cover Braking and Accelerating and continue to build from there.
Note: My approach to these instructional articles is that I try to create a collage of what I have read from many different sources, what I have learned through the years and input from our Chiefs. Special thanks to NASA, SCCA and TurnFast for this article.

Braking
On the street, braking and accelerating are done at relatively low levels compared to the vehicle’s capability. The tire traction limits are rarely maxed out. Sure, you can romp on the gas and spin the tires at a light, or slam on the brakes and slide the car a little, but it is very easy to bring the car back under control because the amount of traction you need versus what you have is quite low. In other words, you back way off and you are usually right back in control.
In the rain, or especially the snow, you know you have to be much gentler and smoother with the brakes and with the accelerator. If you lose control on a wet or snowy surface, it can be much harder to regain control. There is much less traction to work with.
Braking and accelerating, when driving on a road race course, even when dry, is treated something like driving on a wet surface – “gently” and smoothly. The meaning of “Gently” is sometimes hard to understand when you consider what we do on a racetrack. More on that coming up. Braking and accelerating are used in conjunction with the corners – you brake going into them and accelerate coming out of them. Because the objective is to have the car moving as fast as possible through the corner, the tires will be utilizing most of the available traction (done right, they should be using 100% of the available traction). You must be very smooth with the use of the brakes going into the corner and the accelerator coming out of the corner. A sharp change in braking or power at these points will upset the car’s traction balance just as quickly as if you were driving on ice. Working within the last 1% of traction means there is no reserve to call upon to regain control of the car. Even the pros very rarely recover a car that has lost control. It is not because they do not know how, it is because there is no traction left to work with. It is imperative to learn how to be consistently smooth in braking and accelerating on a road course.
There are three phases in braking.
• First, braking begins with a rapid, but not instant, application of as much braking force as possible. How rapid the brakes can be applied will depend on the suspension in the car. The stiffer the springs and shocks, the more rapidly maximum braking can be applied. Soft springs will have significant forward roll which will require a little longer and smoother ramp-up of braking to keep the car stable.
• Second, once the car settles onto the front tires, you will be trying to minimize the length of the braking zone, so it will require taking the tires to the edge of locking up. You will need to be very aware of the vibrations in your foot from the pedal and in your hands from the steering wheel to feel that small difference (therefore racing shoes are highly recommended. You just will not feel much from the pedals in Air Jordans). The car will travel some distance using a fairly constant brake pedal pressure.
• The third phase is towards the end of the braking zone when the vehicle has been slowed to near its final speed. Gradually release pressure off the pedal making the transition from full to zero braking force as smooth as possible. During braking, the front tires are under heavy load which increases the available traction. A sudden release of the brakes will abruptly reduce the load and reduce the traction potential of the front tires which at this point are needed for turning into the corner.
The turn-in is one of the points where the car will be the most sensitive to sudden weight transfer transitions as though it were being driven on ice. Indecisive braking resulting in a last second extra tap, or a sudden release of the brake pedal will unsettle the car’s handling and force the driver to slow down to gain control and hopefully avoid a spin.
As the braking zone completes and you ease off the brake pedal, you will have to apply some throttle to reach a steady state of neither acceleration nor deceleration. Depending on the shape of the turn, the steady throttle zone will vary, but with a typical late-apex corner, it will be from the turn-in to just before the apex.

Accelerating
From this point to the turn’s exit point, the use of the accelerator must be equally smooth for the same reasons they were for braking. Through the turn, the car will have settled with a certain loading of each tire. A sudden change in that with the accelerator can also upset the available traction on one or more of the tires and cause a loss of control. Controlled use of the accelerator is a matter of depressing and releasing it in smooth motions. Do not make sudden jerks in pedal position.
In a typical street car, applying the accelerator smoothly is not as difficult to master as smooth braking. Once a car is moving fairly fast, most street cars just do not have enough horsepower to really cause trouble under most acceleration circumstances. Even the factory exotics and highly modified street cars rarely have more than 400 horsepower and in a car weighing 2500 to 3200 pounds, that just is not an overabundance of power to learn to control. The typical professional open wheel cars weigh 1500-1800 lbs and have 700-900 horsepower. That is about 5 times the power to weight ratio of your typical street sports car. Nevertheless, whether it is relatively easy to control or not, the introduction of 5 hp too much at the right point, and you may as well have an extra 900.
Coming out of a turn, as soon as the car begins to straighten out, gradually apply more power the straighter the car gets. Use smooth consistent pedal pressure – indecisive on and off stabs will end up being slower than a smooth increase. Because most street cars are not overly sensitive to rough throttle control (although there are definitely some exceptions), it is easy to develop bad habits with the accelerator. Even though you may not have to be ultra smooth to maintain control, having the discipline to develop smooth control will still improve lap times and should you have the opportunity to drive a higher horsepower car, you will have the skills to keep the car pointed in the right direction.
I hope you found this article helpful and is something you will consider as you continue to travel down the path (and slippery slope) of high performance driving.
Tom Iervolino, NNJR – Track Chair