Tires are rated according to their load-carrying capacity and speed rating. The load-carrying capacity is the maximum amount of weight that the tire can support, while the speed rating is the maximum speed at which the tire can safely operate.
There are a few different ways that tires can be rated. The most common way is by using the P-metric system, which rates tires according to their load index and speed rating. The load index is a number between 1 and 126 that corresponds to the maximum weight that the tire can support. The higher the number, the greater the weight capacity.
The speed rating is represented by a letter and corresponds to the maximum speed at which the tire can be driven for extended periods of time without suffering any damage. The ratings range from A (the lowest) to Y (the highest).
Another way of rating tires is by using UTQG, or Uniform Tire Quality Grading. This system assigns three ratings to tires: treadwear, traction, and temperature resistance.
Treadwear is judged on a scale of 100-0 and corresponds to how long it takes for tread wear indicators to become visible on the tire surface. 100 indicates normal wear, while 0 would indicate no wear after 7200 miles (12000 km) of driving.
Traction is given a grade from AA (the best) to C (the worst), based on how well a tire performs in wet weather conditions such as rain or snow. Temperature resistance is given a grade from A (best) to C (worst), based on how well a tire resists heat build-up when driven at high speeds for extended periods of time.