Tech Tips: Understanding Tire Temperatures
It is the combination of proper inflation and chassis alignment that gives your tires optimum GRIP on the racing surface. But how do we know what pressures to run and do we set them cold or hot? And once we have the tire pressures set properly, how can we tell if the car's alignment has the proper amount of camber? These are but a few of the mysteries that can be answered by taking tire temps and pressures.
First, tire temperatures are meaningless, or nearly so, after a "cool down" lap. To obtain meaningful data, the driver needs to complete a hot lap and come directly into the pits where the crew immediately takes the temperature of each tire in three places (outside, middle and inside). Begin with the most important side of the car - left side tires for a predominantly right hand track and vice versa. Rear tires first in a rear or mid-engined car and front tires first in a front engined car.
Record the tire pressures before you go out (cold) and then after you come in off the track (hot). Do this after you record the temperatures since the temp drop much faster than the pressures do.
The objective is to get the tire to work effectively across the entire face of the tire (all readings the same). In reality this will probably never happen, but you should shoot for no more than a 20° F spread across any one tire. If the center temperature is higher than the average of the inside and outside temps, the tire is over inflated - try reducing the pressure in 2 lb. increments. If the middle temp is lower than the average of the inside and outside temps, the tire is probably under inflated - try increasing the pressure again in 2 lb increments. Once the pressures are set correctly, then look for major differences in temperature side to side. If the inside temp is always significantly hotter than the middle or outside, the chassis may have too much static negative camber adjusted into it. Caution: This reading can also occur if you take the temps after a cool down lap when you have not worked the chassis hard enough to effectively use the full face of the tire - in effect you have driven on only the inside edge of the tire due to the static negative camber in the chassis alignment. Don't mistake this for too much negative camber, try taking the readings immediately after several hot laps. If the outside temperature is consistently hotter (by more than 10° F) than the inside, try dialing in a bit more negative camber.
Once these pressures and camber are set optimally, then look for differences in temps of the front tires compared to the rears. Again, they will never be the same due to engine placement and drive wheels, but differences in temps can confirm your "seat of the pants" feel about how the car is handling. Does the car push (understeering) in many of the corners - then the front tires will probably be hotter than they should be due to the excessive slip angles that generate the push. In this situation try experimenting by softening the front sway bar (if it is adjustable). If the car feels loose (oversteering) and that is confirmed by the rear temps being considerably hotter than the fronts, then try softening the rear bar.
Remember to first try to adjust the end of the car that is not handling optimally. Only then, when you are out of adjustment on that end should you try an adjustment on the other end of the car. Tire gauges and pyrometers are only two of the important tools to help you get the most out of your car's handling.
At Northstar Motorsports we carry the Intercomp Contact Digital Pyrometer Race Kit as well as an excellent assortment of competition tire gauges.
