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 FAQ #197
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Tyre Side Wall Codes
tyre Size Markings (example: P215/65R15 89H)

Broken down: P= Passenger Other designations are LT = Light Truck T = Temporary (spare tyre)

215 is the width (in millimeters) of the tyre from sidewall to sidewall. A wider tyre has more grip but the bad news is that you lose fuel economy, hear more noise and the tyres don't work as well in the rain.

65 is the aspect ratio The aspect ratio is the ratio of sidewall height to tyre width. With regards to aspect ratio, the larger the number, the taller the tyre sidewall. Tall (60-75) is great for a quiet ride but causes howling in turns. Short (35-55) is better for handling--more for sports cars.

R indicates Radial. This means it is constructed with a series of support belts sideways under the tread. Other designations include B for Belted Bias and D for Diagonal Bias The standard, and what you'll see most often, is R.

15 is the wheel (or rim) diameter, in inches.

89 is the load index H is the speed rating Speed ratings indicate the top speed under ideal conditions. Higher-rated tyres are usually made of softer rubber and will have shorter UTQG tread life.

Here are a few of the more common speed ratings: R= 106, S=112, T=118, U=124, H=130, V=149, W=168, Y=186. Along with this speed rating, you have a load index which indicates the approximate weight the tyre can carry. Some of the more common load weights are as follows: 85 = 1,135 pounds, 86 = 1,168 pounds, 87 = 1,201 pounds, 88 = 1,235 pounds.

UTQG Ratings

Passenger car tyres are accompanied by a UTQG Rating (Uniform tyre Quality Grading, mandated by the Federal Government) which rates the tread life of tyres by looking at tread wear, traction and temperature resistance. The UTQG Rating is usually found opposite the tyre size markings and will be in three separate ratings: treadwear, traction and temperature.

The treadware grade standard is 100. A grade of 200 means the tread would wear twice as well as a tyre graded 100.

Traction grades run from AA to C, with AA being the highest grade and C meaning the tyre brakes poorly on both wet concrete and wet asphalt.

Temperature grades rate the tyre's resistance to and ability to dispel heat. Those grades are A (resists heat well), B (not as good as A) and C (passes minimum safety standards.) Keep in mind that heavy loads, under-inflation of the tyres, and high speeds can all affect the tyre temperature.

You should note that these tyre grades rate tyres measured under controlled conditions. Factors such as driving habits, road conditions, climate, etc., are not considerations and may affect the actual performance of your tyre.

DOT

DOT (Department of Transportation) indicates the tyre is in compliance with applicable DOT safety standards. Next to DOT is an identification or serial number--codes that designate where and when the tyre was produced.
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FAQ Posted by Dave-Retired
Info Created: 07 October 2009
Last Updated: 18 December 2015
 

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