When shopping around for a new set of tires for your British car, one can never find a salesman to answer basic questions. On the tires, the letters and numbers can tell you its size, performance and life expectancy. The P-metric system of marking tires is favored by most U.S. manufacturers.
The basic number shown in the following graphic is P205/60R 15 89H. The breakdown of the number is as follows:
P = Means the tire is for passenger cars
205 = The width of the tire's cross section in millimeters
60 = Refers to the ratio of a tire's height to width. This tire is 60% as high as it is wide. Steering response is quicker if this number is relatively
R = Means it's a radial tire
15 = This is the tire rim diameter in inches
89 = Refers to the load index. In this case, the tire's top load is 1,279 pounds at maximum inflation.
H = This is the speed rating. This particular rating means the tire is certified for speeds up to 130 mph.
M+S = Any combination of those letters means the tire meets the Rubber Manufacturers Association definition for a snow tire.
Treadwear 160 = Refers to the tires life expectancy. Multiply that number by 200 for the likely mileage under normal driving conditions.
Traction B = This is the tire's performance on wet roads. "A" is the best grad with B and C following respectively.
Temperature A = This indicates the tire's ability to withstand heat at sustained speeds. Like the traction rating, A is the best rating with B and C following respectively.
The treadwear grade should be used the same way you would use the "unit price" in the supermarket. It is the best way to ensure that you are getting the best tire value. For example: if one tire cost $100 and has a treadwear grade of 300, and another tire costs $80 and has a treadwear grade of 200, which tire is the better buy?
First tire = $100/300 = .33 cents per point.
Second tire = $80/200 = .40 cents per point.
The first tire at .33 cents is cheaper than .40 cents