Tires are the ultimate connection between the car and the racing surface. That basic principle is not a new one, but a concept that has always been at the forefront when trying to understand ways to increase handling performance in a race car. It is again at the very top of the list when we discuss traction under power.

There are five elements that influence the amount of traction that a set of dirt or asphalt tires, the rears in this case, will develop

1. Vertical Loading-Increasing the amount of vertical loading (weight) on a tire increases the available traction, but in a nonlinear way. As we increase loading on a tire, it will gain traction, but not in exact multiples. If a tire has "X" amount of traction with 400 pounds on it, the traction will be less than double as we apply 800 pounds of loading to it. The amount of traction will be less than 2 times X.

2. Contact Patch - The size and cross-sectional loading of the contact patch helps determine how much traction we will have for a particular tire. An added area related to the contact patch and traction involves grooving and siping dirt tires and will be discussed later on.

Reducing the air pressure will usually increase the size of the tire contact patch. That would seem to enhance traction, but excessively low or high pressures may reduce the loading on portions of the tire so that the total loading of the tire is reduced and we end up with less available traction for that tire. There is an optimum operating air pressure for each tire that will offer maximum contact patch area and equal loading across the width of the patch.

Camber also affects the size and cross-sectional loading of the contact patch. The correct camber angle compensates for the deflection of the tire sidewalls as the lateral force is applied when we turn the car. More or less camber than ideal means one side of the tire will support more weight than the other, which also reduces traction.

3. Chemical Makeup - The chemical makeup of the compound of the rubber will help determine how much traction is available from a tire. A softer tire will provide more traction, but the maximum amount of traction that can be utilized over a long period of time depends on how the tire holds up to heat and wear. A tire that is a little harder may sometimes hold up better and be faster towards the end of the race when the tires have built up a lot of heat and are well worn after a number of laps.

4. Angle of Attack - The amount of traction available from a tire can actually be enhanced simply by increasing its angle of attack relative to the direction of the car, but only up to a point. From straight ahead, we can turn the wheel and, with each degree of angle of deviation from the direction of travel, the traction in the tire increases. There is a point we reach where the gain is reduced and we approach the limit of attack angle that the tire can handle. Once that point is reached, going beyond causes a sudden loss of grip and traction falls off drastically. This principle is true of all four tires whether front or rear. We will provide more on this subject later.

5. Equal Loading - An opposing pair of tires (tires on the same axle at the same end of the car) will develop maximum traction when they are equally loaded. That is a generally true statement, but upon more careful examination of how we do things in circle track racing, there is a unique situation where that is not exactly true.

The situation is when we have a tire on one side of the car (usually the left side) that is built with a softer compound than the opposing tire whereby it may be able to develop more grip under the same loading as the opposing tire. So, increasing the vertical load on the inside tire with the goal of attaining equal loading for both tires, by whatever means, may not actually generate more traction because of the difference in grip per pound of vertical loading created by differences in compounds.