V1.0 Dec 20 2008

The intent of this work is to share all the lessions I learned during my racing career; dumping as much of my brain and hard-earned knowledge into the public record as I can. It is, however, NOT public domain. I reserve the copyright for myself. You may NOT duplicate this elsewhere - including linking images - without my express permission - and this is the age of Google, folks, I WILL find you if you post it elsewhere. Otherwise, read and enjoy, and put this all to good use. Go fast!. DG

The Basic Goal

OK, so you've decided to try and improve the performance of your car.

What does that really mean? What effect are we trying to achieve here?

That may seem like a simple, perhaps even stupid question to ask - except that far too many people dive right in without actually considering what the end state of all this work really is. We need a mission, or a goal, so that we know when it is we are finished, and so we can map a course to get from where we are, at the start, to that ultimate goal.

The ultimate effect should be "win races" - and that implies completing the event course in the shortest possible time relative to the other competitors.

But what does that entail? What does "covering the course in the shortest possible time" involve?

A decent first crack at defining the answer might be something like this:

1. The car must gain speed (accelerate) as quickly as possible;
2. The car must go around a corner as quickly as possible; and
3. The car must lose speed (deaccelerate) as quickly as possible.

Let's examine each of those goals in turn.

1. The car must accelerate as quickly as possible. This is immediately obvious to anyone who has participated in a drag race. Given a straight line, and no artificial limit on top speed, he who gains speed the quickest covers the ground in the least amount of time and so gets to the finish line first and wins the race.

2. The car must go around a corner as quickly as possible. Intuitively, we know that there is a speed at which one can negotiate a corner without sliding off of it or spinning out. The higher that speed is, the faster we cover the ground in the corner and the less we have to slow down before entering the corner.

3. The car must deaccelerate as quickly as possible. Given that we may have to slow down to our maximum cornering speed before entering a corner, the faster we can slow down, the longer we can stay going fast before having to start slowing down. It may seem counter-intuative at first that being able to stop quickly makes you faster, but think of it as playing "chicken" with the corner - the faster the car slows down, the later you can wait before you have to slow down.

Speed up, turn, slow down - seems simple, doesn't it?

It isn't.

Part of the problem is that the car almost never does one of those three tasks in isolation. Very rarely are you just speeding up, slowing down, or turning - there is usually an element of either speeding up or slowing down in conjunction with a turn.

But the other part of the problem has to do with exactly what "speeding up", "slowing down", and "turning" really means.

All three of these actions require the car to exert force on the road surface, and the interface between the car and the road surface is the tire. Whenever we talk about "speeding up", "slowing down", or "turning" what we mean by that is getting those four tires to generate force - forwards, backwards, or sideways. We call the ability to transmit force to the road surface GRIP.

Physics time. The basic equation we are talking about here is:

Speeding up, slowing down, and turning are all accelerations. The car (and driver) have mass. Therefore, in order to produce larger accelerations - which make us faster so we can win races - we need more force, or grip.

If we pretend for a moment that we have to ability to change the physical properties of the tires we use (which really isn't that too far reduced from reality, given that there is usually a "best tire" and we had better be using it if we want to win) maximizing our ability to speed up, slow down, and turn is really about maximizing grip. Each tire can produce a certain maximum amount of grip before it lets go and starts sliding, and what we want to do is make sure that tire is producing its maximum grip so we can use it to accelerate the car.

(We can also reduce the mass of the car/driver, but for now we'll assume the rules stipulate a minimum weight -- as they usually do - and that we are already there)

But remember - we have four tires, not just one. It's not enough to maximize the grip out of any one tire; we have to consider all four tires as a system, not just as individual tires.

And we have to do this while the car is:

1. Accelerating in a straight line;
2. Deaccelerating in a straight line;
3. Deaccelerating and turning;
4. Just turning;
5. Accelerating and turning; and
6. Back to accelerating again.

Complex, neh?

Thankfully, there is a way to simplify how to represent these steps.

The Phases of a Corner

We can break any corner down into three distinct phases:

1. Corner Entry in which the car transitions from 100% braking, through some degree of cornering and braking at the same time, to 100% cornering;
2. Mid-Phase in which the car is just cornering; and
3. Corner Exit in which the car transitions from some degree of cornering and accelerating at the same time to 100% acceleration.

Every race course is a succession of these three phases chained together: entry, mid, exit, entry, mid, exit over and over again. Depending on the design of the course and the shape of the corner, these phases will have different durations and different directions, but it is always entry, mid, exit.

So then, here is our goal:

Everything else that this book talks about is how to achieve this goal. We have four tires. They are all we have to create accelerations on the car. The larger those accelerations, the faster we go, and the faster we go, the more likely we are to win.

There is a way to graphically represent this, and it is very useful to help conceptualize this goal. It is called the "traction circle' or "friction circle" in most literature, but I like to call it the GRIP CIRCLE. And as soon as I get back to civilization (and my tools) I'll write about it here. But not today.

Driver Effectiveness   | Table of Contents | Tires