Deciphering Your Tires

Photo courtesy of Kiko Alario Salom/Flickr
Photo courtesy of Kiko Alario Salom/Flickr

We all do it. We walk into a tire store when we need new tires and the clerks asks us what size tires we have on, currently. Cue the blank stare from us. How can they expect us to know what all those numbers mean!?!?! P225/75R16? What does that mean?!?

P225/75R16

I’m going to break it down for you, so next time someone asks, you will know what they are talking about.

Service Description

The first letter you see tells you all you need to know about how that tire is supposed to be used. There are a few different designations that are possible:

P – Passenger Car
LT – Light Truck
ST – Special Trailer
T – Temporary

Tire Width

The second designation in the mixture of numbers is the overall tire width. It is measured from sidewall edge to sidewall edge. The larger the number, the larger the tire. 195 and 215 are small tires, for small cars. If you know of anyone with a big, jacked up 4×4 truck then they probably have 325-395 sized tires. Unless you know what you’re doing, or a tire professional says it’s ok, stick with your manufacturer’s recommendation on tire sizes.

Aspect Ratio

The first number after the forward slash is the aspect ratio of the tire. It’s measured by it section height compared to its section width. Therefore, a “65” tire means the sidewall¬†of the tire is 65% ¬†of the height. This number comes in handy when you want a lower profile tire.

Internal Construction

Up next is a letter designation that signifies how the tire is made. There are 2 possibilities:

R – Radial (the standard for all passenger cars)
B – Bias (for special truck and trailer applications)

Rim Width

The last number on the string of number is the most simple and the one that is most important. The width of your wheel. As you probably guessed, the rim width much match the wheels you have on your car. If they don’t then you’ve got a big problem, or you’ve wasted money on either rims or tires.

There you have it! So next time you get asked about your wheels and tires, you’ll have an idea of what all those numbers mean!