How To Read Your Tires

There is a lot of important information on the side of your tires. In this article, we'll help you understand what it all means so that it's easier for you to pick your next set of tires.

Take a look at the overview diagram below.

Let us walk you through each of those items on the diagram.

Tire Type

You might see a letter code as the first character of your tire size. It may or may not be there.

The meaning of those letters is as follows:

P or no letter - means Passenger tire. This class covers regular cars, SUVs, crossovers, minivans, smaller pickup trucks, and EVs (electric vehicles).

LT - means Light Truck. This class can be used on heavier vehicles or those carrying heavier loads. You might see those on 3/4-ton or 1-ton trucks and some SUVs.

ST -means Special Trailer. This class is meant for all kinds of trailers.

Tire Width or Section Width

Tire Width, sometimes called Section Width, is measured from sidewall to sidewall when mounted and inflated but not loaded. It's measured in millimeters.

Aspect Ratio

The number right after the forward slash is the Aspect Ratio. It's the height of the tire from rim to top of the tread as a percentage of the Tire Width. 

A simple formula to remember:

Tire Height = Tire Widt x Aspect Ratio/100.

Example: 

If the tire size is "235/45R18" then the tire height is "235mm x 45/100 = 105.75mm".

The lower the Aspect Ratio the lower the profile of the tire.

Construction Type

The letter after the Aspect Ratio means Construction Type and it comes in two flavours:

R - radial. In this construction type, the internal cords are laid perpendicular to the direction of travel. This is the standard for the majority of tires today.

D - diagonal or bias-constructed. The internal cords are laid at an angle to the direction of travel. Some trailers and motorcycle tires use this construction type.

Tire Diameter

Tire Diameter is simply a diameter of the rim, that can be used with the tire, in inches.

Tire Load Index or Tire Load Rating

A tire load index (or tire load rating) is a number, that corresponds to the maximum weight a tire can carry when properly inflated.

The higher the number the more weight the tire can handle. Passenger tires usually range from 80 to 100.

You can find more details and the Tire Load Index Chart here.

Tire Speed Rating

The tire speed rating is a letter code that informs customers how fast they can drive using the tires.

It's not only about speed, though. It also affects ride comfort, wear, and cornering ability.

You can find more details and the Tire Speed Rating Chart here.