Tire hardness can be a critical factor in setting up a race car. A tire that's too hard may sacrifice traction, while a tire that's too soft may give great traction but wear too quickly, and an unmatched set of tires may result in an ill handling car. To properly set up a car, a measure of tire hardness is necessary, and the easiest and most cost-effective way to obtain such a measure is to use a durometer.
The Type A durometer as specified by ASTM D-2240 is the gauge used by tire manufacturers to measure hardness of tire rubber. The gauge gives readings of hardness in durometer points on a scale of 0-100, with 100 being the hardest reading. Some race tires come from the factory with the durometer hardness noted on the side wall, but factors such as ambient temperature, track temperature, usage, and age of the tire can change the actual hardness of the tire from the factory hardness.