How to Read the Markings on Your Tires
This is going to be a long one, so let’s jump right in.
What do the markings on a car tire mean?
Reading Your Tires
Tire designations, at least in the United States, are printed from left to right, containing a few letters and numbers bunched together. The following explanation will define the bunches in the order they appear. We will use the following tire designation from a 2018 Toyota RAV4 tire as an example: 235/55R18 100H.
- “235” – Width of the tire. The first three digits will always indicate this. It is can be metric or English measurement (in this case, it is in millimeters; 235 mm converts to 9¼ in). It is not uncommon for a truck or SUV tire a “P” or “LT” before the first three digits to indicate what type of vehicle the tire is meant for.
- “/55” – Height of the sidewall. The slash and the next two digits combine to make the aspect ratio, which is given as a percentage. So, the height of the side wall is 235 multiplied by .55 (e.g. 55%). In this case, that comes out to 140 mm or 5½ in.
- “R18” – Type of construction and rim size. Most tires have radial-ply construction, indicated by “R.” A tire with a Z speed rating—the highest speed rating available—is listed directly after the construction type (in this example, it would be “RZ18 100” instead of “R18 100H.”). The numbers tell what the diameter of the rim is, so an “R18” tire would fit an 18-inch rim.
- “100” – Maximum weight load. These numbers match up to a number on a load index, which can be found in your vehicles owner’s manual and at your local tire shop. These can change from vehicle to vehicle and brand to brand, but mostly stick to an industry standard. A load weight of 100 comes out to 1764 lbs per tire in most cases.
- “H” – Speed rating. This is the max speed a tire is rated to reach and still work as intended. Each letter indicates a specific maximum speed (“H” is rated for up to 130 mph). As mentioned before, tires with a “Z” rating are listed directly after the construction type instead of the weight load.