The r-comp performance tires on a track car are critical because they translate the driver's steering, brake and accelerator inputs into motion. The driver continually tests the limits of tire adhesion, especially in road course events. The track tires ultimately determine how fast the driver can accelerate, corner or brake.
Track tires are substantially different from those on a passenger car. The three biggest differences are:
1. Track car tires are much wider – up to 14 inches wide, whereas the typical passenger car tire is 7 inches wide.
2. Track tires will not have any tread blocks to maximize the amount of rubber touching the track surface.
3. The rubber on the face of the track tires is extremely soft. It is more like a soft rubber eraser than anything else, and very unlike the hard rubber found in passenger car tires.
Between the size of the contact patch of a track tire and the softness of the rubber, the track tires have incredible adhesion. The severe motorsport driving conditions cause track tires to deteriorate very quickly compared to those on passenger cars. Tires on a passenger car are designed to last 40,000 to 60,000 miles, whereas track car tires may last only 500 to 1000 miles.
Track Tire Temperature
Track tires get very hot due to tread flex and friction generated by rotational speed and by cornering and braking. The higher the load and the higher the speed, the hotter the tire will get. But that heat will not be distributed evenly. One tire may run hotter than the others, or one area of the contact patch may be hotter than another. If you can accurately measure tire temperatures and observe how those readings are distributed across the tire, you can adjust tire pressures and suspension to achieve improved performance.
There are two tools available for measuring temperatures on track tires. One is an infrared thermometer. Infrared thermometers run on thermal, or infrared energy (“IR”), which is light with a long wavelength that makes it invisible to the human eye. It is the part of the electromagnetic spectrum that is perceived as heat. Unlike visible light, in the infrared world, everything with a temperature above absolute zero emits heat, even very cold objects like ice. The higher the object's temperature, the greater the IR radiation emitted. Infrared allows us to see what our eyes cannot.
When taking track tire temperatures it is important to keep the tires as close to operating temperature as possible. Therefore, you must run two to three hot laps to heat the tires and get into the pits quickly. Temperature readings are taken as soon as possible, since the tread surface is cooling rapidly.
A second method calls for using contact thermometers. Contact thermometers with a piercing style thermocouple probe are significantly more reliable than IR because they are more accurate. When determining the temperature of race tires, you gauge the internal temperature of the tire tread, not the tread surface.
The internal tread temperatures do not fall as rapidly as the surface temperatures, so by measuring temperatures 1/8 of an inch into the tread, you have a little more time to make an accurate measurement of a hot tire.
Using an IR thermometer, you will get a surface reading that may be 10-40 degrees cooler than temperatures taken with a probe type thermocouple.
Three readings are taken on each tire: inner tread, center tread and outer tread. Inner and outer readings are taken one inch from the tread shoulder. Write down the readings for evaluation. A typical operating range for a DOT-R tire is 180˚F to 200˚F with a hot pressure of 32-40 psi. There should be not more than a 20 degrees difference in temperatures across the tread, with the inside being slightly hotter than the outside.
Tire temperatures are also useful in fine-tuning the suspension geometry. Tire temperatures will tell you what part of the track tire is contacting the track and how it is working. Ideally, the entire tire tread surface should be in contact with the track and working as close to equal as possible.
Use the following table as a general guideline to interpret readings and make adjustments to the car:
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