Last Updated 27 Jul 2015

Reading a Tyre

You can find out all the basics about a tyre simply by reading the information on the side (or sidewall).

Tyre Sidewall Markings
Tyre Width

Width of the tyre measured in millimetres from sidewall to sidewall. The tyre in the diagram below is 185 millimeters wide

Aspect Ratio

Ratio of the height of the tyre's cross-section to its width. 65 means that the height of the sidewall is equal to 65% of the tyre's section width.

Wheel Diameter

The width of the wheel from one end to the other. The diameter of the wheel in the diagram above is 15 inches.


This tells you how the tyre was put together. The "R" stands for radial, which means that the body ply cords. These cords are layers of fabric that make up the body of the tyre, and run radially across the tyre from bead to bead. A "B" indicates the tyre is of bias construction, meaning that the body ply cords run diagonally across the tyre from bead to bead, with the ply layers alternating in direction to reinforce one another.

Load Index

Indicates the maximum load in kilograms that a tyre can support when properly inflated and run at its maximum speed. You will also find the maximum load in pounds and in kilograms elsewhere on the tyre sidewall.

Speed Rating

Shows the maximum service speed for a tyre. "H" for example means that the tyre has a maximum service speed of 130 miles in one hour. Please note that this rating relates only to tyre speed capability, and is NOT a recommendation to exceed legally posted speed limits; always drive within the legal speed limit.


Means the tyre is compliant with all applicable safety standards established by the U.S. Department of Transportation (DOT). Adjacent to this is a tyre identification or serial number; a combination of numbers and letters with up to 12 digits.

Tyre Type

American markings define the proper use of the tyre. "P" means this is a passenger car tyre. "LT" means it is for a light truck.


Stands for Uniform Tyre Quality Grading, a quality rating system developed by the US Department of Transportation (DOT).