Tyre education
How to read inch sizes:35X12.50R15LT E
Diameter : 35
The Diameter of this tire size is 35 inches. The first number in a high flotation tire size is the overall diameter of the tire.
Section Width : 12.50
The width of this tire size is 12.5 inches. The second number in a high flotation tire size is the width of the tire in inches.
Tire Construction : R
The tire construction of this tire size is R for radial. This letter is for how the tire is constructed. Radial is the standard construction method for almost all tires.
Wheel Diameter : 15
The wheel diameter of this tire size is 15 inches. The tire is designed to be mounted on an 15 inch wheel diameter.
Tire Class : LT
The tire class of this tire size is 'LT' which means it is a Light Truck tire.
Load Range : E
Tire load range of this tire size is 'E' which means it has a 10 ply tread. Other load ranges include B: 4 ply, C: 6 ply and D: 8 ply.
How to read metric sizes:P255/60R17 102V
Tire Class : P
Tire tire class of this tire size is 'P' which means it is a passenger car tire. The first letter in the tire size designates the tire class. An 'LT' would be a light truck class and no letter would be a euro-metric tire.
Section Width : 255
The width of this tire size is 255mm wide. The first number in a metric tire size is the section width of the tire.
Aspect Ratio : 60
The aspect ratio on this tire size is 60. The second number in a metric tire size is called the aspect ratio and means that the sidewall height is 60% of the section width.
Tire Construction : R
The tire construction of this tire size is R for radial. This letter is for how the tire is constructed. Radial is the standard construction method for almost all tires.
Wheel Diameter : 17
The wheel diameter of this tire size is 17 inches. The tire is designed to be mounted on an 17" wheel diameter.
Load Index : 102
The load index of this tire is 102 - 1874 lbs. This number is the load index and the maximum amount of weight the tire can carry. A higher number means the tire can carry more weight.
Speed Rating : V
The speed rating of this tire size is V - 149 mph. This letter is the speed rating of the tire and indicates the maximum speed the tire can sustain.
Converting Metric to Inches
There are two ways that tire manufacturers display tire size, inches and metric. How to read tire size in inches is very straight forward. Example A : 33X12.50R15 The first number is your overall diameter of the tire. In this example the tire diameter or "height" is 33 inches tall. The second number represents the width of the tire. In most cases with inch measurement tires the width will have a .50 decimal after the initial number. In example "A" this reads 12.50, meaning the tire width is 12 and 1/2 inches. The final number simply is the wheel size or "diameter" of the wheel that the tire will fit on.
How to read tire size with a metric measurement is a little more difficult and usually takes a calculator to get exactly right.
Learn About Tire Sizes
Example B : 285/75R16
On metric tires the first number is your width of the tire in millimeters. In example "B" this reads 285mm. There are 25.4 mm in one inch. To convert 285mm to inches you divide 285 by 25.4 to get 11.22". So the width of a 285mm tire is 11.22". The next number represents the percentage of the width (285mm or 11.22") that is the sidewall height of the tire. In this example the side wall height of the tire would be 75% of 11.22" which is 8.41" or 214mm. To then get the overall diameter of the tire you would add the two sidewalls measurements and the diameter of the wheel. In example "B" the last number "16" is the wheel size the tire will fit on. Therefore the sidewall twice would be 8.41 x 2 = 16.82 plus the wheel "16" makes the tire height 16.82 + 16 = 32.82. So a 285/75R16 metric tire would calculate to an inch measurement tire of 32.82X11.22R16. Remember, not all tire sizes are manufactured in both metric and inch sizes so learning how to read tire size can be a valuable tool for anyone in the market for new tires.
