There are many different forces acting on your car. We could get into a real in depth discussion of them here, however if you really want the detailed principles about the physics acting on your car, check out the handling web site we have listed in the back of this manual. If you want to know only what you need to set up your car, read on.

To begin, you have to understand that setting up your car is nothing but managing how you transfer the physical weight of your car to maximize traction. That’s all we are dealing with. You have a weight (your car) that you want to travel in a certain direction (the racing line) on a particular surface (the track).

Center of Gravity
First we’ll discuss the weight. The weight of your car is focused in one location, the Center of Gravity (we'll abbreviate it "CG"). The CG of your car is an imaginary point to which if a string were attached at that exact point, the car would be perfectly centered and level - it would not lean to the left, right, front, or back. In 4WD touring car racing, you want your CG as close as possible to the center, left to right and front to back, as possible. That would mean that 50% of the car’s weight would be on the front wheels and 50% would be on the back wheels. 50% would be on the left tires and 50% would be on the right. This also means that each tire is carrying 25% of the cars weight and that the weight on all four tires will be equal. Remember the whole "balance" thing from chapter 2?

The CG Shifts as the Car Moves
Now, just because your car may have equal weight on all four tires when it is standing still, doesn’t mean that it stays that way. The weight will shift as the car moves. As you accelerate, the CG will shift to the rear of a car just like when you feel like you get pushed into the seat of a real car when it accelerates. Because of this shift, the rear tires will carry more of the weight of the car on them than the front when the car is accelerating. When you brake or slow down, the opposite occurs and the front tires have more weight on them than the back. As you turn, the chassis will roll and the CG will shift to the outside of the car (if the car is turning left, the weight shifts over to the right). The tires that are on the outside of the car will thus have greater weight on them than those on the inside.

Because your car can, and does, turn while accelerating or braking, the CG will usually move towards one tire. For instance, if you are slowing down to enter a right turn, the CG moves forward to the front tires. As you turn right, the CG will shift to the left. Since you are slowing down and turning right, the weight on the left front tire is more than any of the other tires.  The right front and left rear have about the same amount of weight. This may seem not to make sense, but remember: the car is turning right and putting more weight on the left side tires, thus making the left rear heavier, but the car is also slowing down at the same time putting more weight on the front tires. This almost equal weight between opposite tires (either left front and right rear or right front and left rear) is often referred to as corner weight. In our example, the tire with the least amount of weight on it would be the right rear tire. In general, the more weight that is on a tire the more traction ability it has.

Keep the Weight Low
As you can see, the CG of a car is constantly changing as the car negotiates its way around the track. The weight management part of a car’s set up is controlling how far that weight moves in any one of the two planes (front to rear is one plane while side to side is the other) and how quickly it moves from one position to another.  One other thing to note about CG is that the distance from the ground to the CG plays a big part in handling.  The higher the CG is, the more likely the car is to flip over during a turn. We’ll discus why this is later but keep in mind when buying hop up parts that it is important to keep your CG low in the car for this reason.

Traction
The next part of your set up is traction. Traction is pretty simple to understand, it is the friction between the surface you are running on and the tires themselves and the grip that this friction provides. This means that the tires themselves play an important part in how hard you car can turn. The more traction you have, the harder you can corner. But as we mentioned before, the surface of the track also plays a part in this. If it is a dusty, bumpy track, it will provide less traction than a swept, clean, smooth, treated track will meaning that you won’t be able to corner as hard.

With this being said, this does not mean that there is no limit to the amount of traction you may have. Weight and traction are related. If too much force is applied to a tire, the tire will not have enough traction or grip between it and the road and it will start to slide rather than grip. A very little amount of slip is not bad (so little actually that you can’t see it on the track) but too much and you loose traction and the car begins to spin or slide. We’ll talk more about grip and traction when we discuss tires in the next section.

Can You Have Too Much Grip?
Believe it or not, it is possible to have too much grip. If you have a tremendous amount of grip, such as running very sticky tires on a very high traction track, your car can do what we call a "traction roll". A traction roll is when the car flips over for apparently no reason during cornering. Sometimes the car is assisted by lightly touching a corner dot or another car while turning. Having too much traction and too much weight transfer causes this. The weight transfers so far that all of the weight is placed on the outside tires while the inside tires come off the ground. However, the outside tires do not loose their grip with the surface. If the weight continues to shift or is shifting so rapidly that the driver cannot correct, the car will traction roll. Obviously, having your car flip over every turn isn’t the fastest way around the track.