From the Chapman Report - February 1991

By Kiyoshi Hamai

Tire makers around the world are standardizing the ratings and the way they designate the sizes of tires. Typically a tire will be marked... 205/60-13. The 205 is the width in millimeters and the 60 refers to the aspect ratio, or the height of the sidewall as compared to the width (sidewall to sidewall) expressed in terms of a percentage. Thus 60 would mean a 60% aspect ratio or the height of the sidewall is 60% of the width or .60 x 205 or 123mm. The 13 is in inches and refers to the diameter of the wheel used.

Now comes some new numbers and letters... Here's an example...

P205/60R13 86H

The "P" is the U.S. means of designating a "P" metric tire size. The 205/60 is the same as above. The "R" refers to the fact that the tire is a RADIAL. The 13 is again the wheel diameter. But, then comes the 86H... The 86 is the load rating designation. It is a code to designate the maximum load that the tire can sustain at the speed indicated by the Speed Symbol, which is the "H" in this case. Load indexes for passenger car tires typically range from 75 ot 100. The Speed Rating is the "H" and refers to the tire's maximum sustained speed rating (see table).

Letter Maximum

Rating Speed

L 120/ 74.5

M 130/ 80.7

N 140/ 86.9

P 150/ 93.2

Q 160/ 99.4

R 170/105.6

S 180/111.8

T 190/118.1

H 210/130.4

V 240/149.1

Z 240+/149.1+