The Racing Surface
New tires are faster not only...
New tires are faster not only because they have better rubber compound qualities over used tires, but also because they have a thicker layer of rubber and that helps to provide a cushion to help fill the gaps in the track surface. As we wear off rubber naturally, the layer of cushion decreases and the tire rides more on the ridges in the track rather than on all of the surface area. Tires that are treated, either legally or not, will conform to the track surface irregularities better and provide more traction. You can overdue softening of the tires to the point of causing excess wear over the same period of time.
The surface we race on largely determines the amount of traction available and we will look at dirt and asphalt tracks separately. On dirt tracks, the amount of moisture dictates the amount of grip the track gives us for the most part. Bumps, grooves, banking angles, and the overall radius all help determine how much grip is available for traction in the corners. The setup related to shocks, springs, and front and rear geometry help determine how much traction will be available for a certain set of conditions.
On asphalt tracks, and even some "dirt" tracks that have been oiled to the point of almost being asphalt, the surface is more consistent and other than holes or bumps and rises in the surface, we can expect the grip to be the same over the course of the event. Flatter banking and older asphalt dictates the need for more traction control efforts.
Now that we have some kind of understanding of just what affects traction in our race car's tires, we need to think out our setups so that we can use that information to enhance the overall amount of traction in our tires.
Much of what we present month to month deals with the components and methods we can use to promote balance in our setups. As you have read above, when we select the correct spring rates, front and rear roll center locations, shock settings, and load distribution, we will then enjoy the most traction our car is capable of.
Engine Torque Promotes Equal Loading
Some tracks and sanctioning...
Some tracks and sanctioning bodies allow the use of tire treatment which softens the rubber compound. This can be a way to limit cost, allowing a team to run otherwise uncompetitive hard, old tires. Other tracks have rules that don't allow this practice, but mostly look the other way and the teams must soak their tires in order to be competitive. Promoters should define and enforce tire rules either way.
There is one effect that helps promote traction that every stock car has, but few realize, it's the effect of engine torque. When we get back on the throttle, the torque from the rotation of the engine, through the driveshaft, tries to rotate the whole rear end in a counter clockwise direction when viewed from the rear. This action, or force, loads the left rear tire as well as the right front. When those two corners are more loaded, the crossweight percent goes up and the car gets tighter. Also, if the RR tire was supporting more weight than the LR tire, then with this effect, the two rear tires would be more equally loaded providing more traction.
A question often asked is why the car does not get loose immediately when we gas it up if the rear tires are already providing all of their available traction keeping the car off the wall. The introduction of power would cause the tires to lose traction if it were not for the added affect of the engine torque. There is no way to enhance this effect and the magnitude is dependent on the amount of torque the engine develops at a given rpm verses the width of the rear tires. The wider the rear track width, the less effect torque will have on adding load to the LR.
As a driver turns the steering...
As a driver turns the steering wheel, the front tires develop an angle of attack relative to the direction of travel of the car. The more the wheel is turned, the greater the angle of attack. With more angle of attack, the front end gains traction up to a point. This is how a driver can compensate for a tight car. Steering angle and steering input are ways we determine how neutral a setup is.
When the steering angle becomes...
When the steering angle becomes excessive, the tire gives up most of it's available traction resulting in a severe push. Either this happens with a very tight setup, or the excess steering angle overtakes the rear in front traction and the car will go loose. This is called the 'tight-loose" syndrome.
Many current dirt tracks as...
Many current dirt tracks as well as some asphalt tracks that used to be dirt have developed a "D" shape. This is caused by having a wall along the grandstand side only and as the track gets raced on and groomed, the back side away from the grandstands gets pushed out. This makes Turns 1 and 4 tighter than Turns 2 and 3. More steering is required for the tighter turns and in Turn 4 it is usually very difficult to get traction under power as opposed to exiting Turn 2.