Speed rating symbols

All tires are rated with a speed letter. This indicates the maximum speed that the tire can sustain for a ten minute endurance without coming to pieces and destroying itself, your car, the car next to you and anyone else within a suitable radius at the time.

 

 

‘H’ rated tires are becoming the most common place and widely used tires, replacing ‘S’ and ‘T’ ratings. Percentage-wise, the current split is something like this: S/T=67%, H=23%, V=8%. Certain performance cars come with ‘V’ or ‘Z’ rated tires as standard. This is good because it matches the performance capability of the car, but bad because you need to re-mortgage your house to buy a new set of tires.

UTQG Ratings

The UTQG – Uniform Tire Quality Grade – test is required of all dry-weather tires (“snow” tires are exempt) before they may be sold in the United States. This is a rather simple-minded test that produces three index numbers : Tread life, Traction and Temperature.

• The tread life index measures the relative tread life of the tire compared to a “government reference”. An index of 100 is equivalent to an estimated tread life of 30,000 miles of highway driving.
• The traction test is a measure of wet braking performance of a new tire. There is no minimum stopping distance, therefore a grade “C” tire can be very poor in the wet.
• The temperature test is run at high speeds and high ambient temperatures until the tire fails. To achieve a minimum grade of “C” the tire must safely run at 85mph for 30 minutes, higher grades are indicative of surviving higher speeds (a rating of “B” is, for some reason, roughly equivalent to a European “S” rating, a rating of “A” is equivalent to an “H” rating.)

There are some exceptions: Yokohama A008′s are temperature rated “C” yet are sold as “H” speed rated tires. These UTQC tests should be used only as a rough guide for stopping. If you drive in the snow, seriously consider a pair of (if not four) “Snow Tires”. Like life, this tire test is entirely subjective.

This information was provided by Christopher J Longhurst