Traction, tread wearing and temperature
It isn’t just size that matters when choosing tyres for your vehicle. There are some other numbers and letters on the side of the tyre that you should pay attention to. You will find the tread wear listed in three digit numeric format such as “320” and the traction and temperature in letters such as AA, A, B, or C.
The tread wear rating is a relative measurement of the tyre’s durability and treads life. It is important to remember that road surfaces, driving habits, and other factors determine actual tread life. Each tyre manufacturer independently determines tread wear through their own tests. Tread wear is not based on any one industry or government standard. The higher the number the longer the tyre should last compared to similar tyres from the same manufacture with lower numbers. A tyre with a tread wear rating of 800 should theoretically last about twice as long as a tyre with a tread wear rating of 400. A longer life tyre will be designed with a harder rubber compound to withstand wear better.
Unfortunately, while a harder compound tyre will last longer it will do so at the expense of some traction – particularly on wet surfaces. The softer tyre compounds will grip the road surface better for improved handling and braking performance. The traction specification is listed beside the tread wear in the form of letters such as AA, or A, or B with AA being the highest grade possible. The traction rating is a measurement of a tyre’s ability to stop on a straight, wet surface under controlled conditions. It does not indicate the tyre’s cornering ability on a wet surface or its traction on ice or snow.
The temperature rating is a measurement of a tyre’s resistance to heat generation under normal operating conditions at recommended inflation pressures. Temperature grades range from A to C, with A being highest rated and therefore most resistant to heat generation. Tyres graded A effectively dissipate heat up to a maximum speed that is greater than 115 mph. B rates at a maximum between 100 mph and 115 mph. C rates at a maximum of between 85 mph to 100 mph. Tyres that cannot grade up to C or higher cannot be sold in the US.