How to Read Tire Size

Tire size is expressed using a code consisting of letters and numbers. It will look something like this:

        P 215/65 R15 95H

The main figures to pay attention to are the tire class (P for Passenger in the example above) and the wheel or rim diameter (15 in the example above).
 

• Tire class P indicates that the tire was designed to be used on passenger vehicles like cars, minivans, and SUVs. Other tire class codes you might see are LT for light trucks and T for temporary, which will be on a spare tire.
• The wheel diameter number can range from 13 to 22. The wheel diameter should be the same as your rim diameter, so if you decide to upgrade your wheel size, you will need bigger rims, and vice versa.

The other figures in the tire code refer to the tire width, aspect ratio and tire construction type.
 

• Tire width (235 in the example above) is always a 3-digit number and is the width in millimeters measured from sidewall to sidewall.
• Aspect ratio (60 in the example above) is the percentage ratio of a tire’s height to its width. 
• Tire construction type (R in the example above) describes how the cord plies are arranged. R stands for radial, which is the standard construction type for most tires.

How do I Know What Size Tires My Car Needs?

There are a few different ways to determine the right tire size for your car.

Check your current tires

If you’re in the market for a new set of tires, the most straightforward way to find out what tire size you need is to check your current tires. You already know they are the right size, so it makes sense to stick with the same. Check the inner sidewall of your tires for a tire size that resembles the example above. 

Check the owner’s manual

Your owner’s manual will include the recommended tire size for your vehicle. Find it in the tire section or look up the manufacturer online to find the tire size they recommend for your vehicle make and model. 

Driver’s side door jamb

The recommended tire size should also be printed on a sticker placed somewhere on the driver’s side door jamb. The code will be similar to the example above. 

Get a professional opinion

If you don’t want to risk interpreting tire size incorrectly, you can always call the mobile mechanics at Firestone Direct. We’ll ask you for details about your vehicle and your current tires and recommend the right size. You can then purchase tires directly from our website, and we’ll deliver your tires and install them for you in a single appointment.