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Decoding Tire Size: Which Size is the Perfect Fit for Your Car?


Buying a new set of tires is about more than driving conditions, tread designs, or how many you need to replace. If you want your car to function at its maximum potential, tire size is actually one of the most important details to consider before you make a tire purchase. There are a lot of different tire sizes out there, but only one will be the ideal fit for the make and model of your vehicle. Luckily, finding the recommended tire size is pretty simple—you just have to know where to look.  


Here’s how to read tire size to ensure you’re choosing the perfect set of wheels for your vehicle.

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Why Does Tire Size Matter?


Your vehicle is optimized to fit a certain tire size, so it’s important to stick to that recommendation or very close to it. Having the wrong size tires on your vehicle can lead to a host of problems like limited steering and handling capabilities, inaccurate speedometer readouts and even disabled antilock brakes and essential engine systems. Beyond safety concerns, the wrong size tires can also cause costly damage to your vehicle rendering it undriveable. While some people choose to upsize their tires, it’s not recommended for the average car owner.  If you’re unsure how to find the right tire size, the expert technicians at Firestone Direct can help—and they’ll make installation easy by coming to you to replace your old tires.

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Firestone Direct mobile mechanics have everything they need to complete your service on-site wherever you are, and get you back on the road. Click Get Started to schedule your next mobile maintenance appointment!

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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.
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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.

Get Started

Schedule your next Firestone Direct appointment!

Firestone Direct mobile mechanics have everything they need to complete your service on-site wherever you are, and get you back on the road. Click Get Started to schedule your next mobile maintenance appointment!