Updated July 8, 2026
In short
Tire sizes look cryptic, but they follow a simple pattern. Once you know what each number means, comparing tires and confirming fitment gets much easier. Here is how to read both common formats.
Most trucks and SUVs use a metric size like 265/70R17. Reading left to right: 265 is the section width in millimeters (how wide the tire is). 70 is the aspect ratio — the sidewall height as a percentage of the width, so a lower number means a shorter sidewall. R means radial construction. 17 is the wheel diameter in inches the tire fits.
A letter before the number, like P or LT, tells you the tire class. P is passenger-rated; LT is light-truck, built with stronger construction for heavier loads and towing.
Off-road tires are often sized in the flotation format, like 35x12.50R17. This one is more intuitive: 35 is the overall tire diameter in inches (its actual height), 12.50 is the width in inches, R is radial, and 17 is the wheel diameter. This is why off-roaders talk about running "35s" — it refers to the overall height.
After the size you will see a load index and speed rating, like 116T. The load index maps to a maximum weight the tire can carry, and the letter is the speed rating. For trucks that tow or haul, do not ignore the load index — undersizing it is a safety issue.
When upsizing, check that the new tire clears your suspension and fenders at full lock and full articulation, and remember that a taller tire changes your speedometer reading and effective gearing. When in doubt, confirm against your vehicle and any lift or leveling kit before buying.
R stands for radial construction, which is the standard for virtually all modern tires.
P is passenger-rated; LT is light-truck, built with stronger construction for higher loads and towing. Trucks that work often need LT tires.
A 35-inch tire is roughly 35 inches in overall diameter. In metric terms that is close to a 315/70R17, though exact dimensions vary by brand.
Yes. A taller tire travels farther per revolution, so your speedometer will read low unless it is recalibrated.