Tire Size Chart: Find the Right Size Tire Size Chart: Find the Right Size

The number/letter markings on the sidewall of your tire provide critical information needed when choosing a replacement. Refer to the tire size chart below to understand how these codes indicate which tire is correct for your vehicle.

Service Type

The first letter in the tire size code is an indicator of the type of vehicle.

  • P for Passenger vehicle – The most common tire size used, this designation includes cars, minivans, light pickup trucks and SUVs.
  • Metric or “Euro-metric” has no letter prefix – These tires are used on European cars, vans and SUVs.
  • T for Temporary spare, a “space saver” or “mini spare" – A temporary spare is intended for short-term use, and must be replaced quickly as soon as the conventional tire is fixed.
  • LT for Light Truck – Medium to heavy duty trucks, SUVs and full-sized vans use this specification, and are designed to carry heavier cargo than in a passenger vehicle.
  • C for Commercial – Designated for a commercial vehicle, likely a delivery truck or van that carries heavier loads than a light truck.
  • ST for Special Trailer service – Designed to be used on a boat trailer or other types of utility trailers.

Section Width

The next set of digits (or first in the Metric service type) specifies the number of millimeters across the tire when mounted, between the widest points from the inner to outer sidewalls. Since this number is metric, divide by 25.4 to obtain width in inches.

Sidewall Aspect Ratio

The number following the slash in the code is a percentage of the section width representing the tire’s sidewall height.

Using P225/50R16 as an example, this tire’s sidewall height is 50 percent of 225 mm.

Internal Construction

Next, the letter following the sidewall aspect ratio indicates the tire’s internal construction:

  • R for radial construction, the most popular tire type
  • D for diagonal or “bias ply” construction
  • B for belted, no longer very common

Tire and Wheel Diameter

The number following the internal construction letter designation is diameter, both of tire and wheel diameters since they must match. Most common today are measurements expressed in even inches, though some trucks and trailers may have a rim diameter expressed in half inches such as 16.5, and others in millimeters such as 390, 365 or 415.

Service Description

The final alpha-numeric combination designates the tires Load Index and Speed Rating. This information is required on all tires manufactured since 1991.

The numeric Load Index represents the weight that the tires can carry and is primarily a reference to replacement of original equipment – you will want a replacement tire to have at least as much capacity as the original.

The Speed Rating code is a letter, and S refers to family sedans and vans, which is what we typically see on passenger cars.

Need new tires? Easily compare brands and types with our Tires Buyer's Guide.

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