Back to all

What's in a Number? (What Tire Numbers Mean)

October 6, 2024

You've probably never paid much attention to the writing on the sides of your tires, but they contain a wealth of information.  There's a long combination of letters and numbers that can tell you a whole lot about what tires your vehicle was designed to be riding on.  Let's check out this example found on an SUV: P245/70R17 108T.

The first letter, P, means it's intended for passenger vehicles.  If there's no letter, it means it's a metric tire.  If there's an LT at the beginning or end that means a tire designed for light trucks.

Moving on to our example, the 245 shows how wide the tire is in millimeters from sidewall to sidewall.  The number that follows in our example, 70, means the height of the tire is 70% of its width.  The letter after that in our example, R, describes the type of tire (on this vehicle, radial).  Following that is the diameter in inches, in our SUV example, 17 inches. 

How much load the tires' sidewalls are designed to take is what that next number is all about (108 in our example).  The higher the load index, the more weight the sidewalls can take.  And the last letter is the speed rating of the tire, in our example, T.  The further along in the alphabet that letter is, the higher its speed rating.  So now you know what those letters and numbers mean.  But why are they important?

When you are getting ready to replace those tires, those numbers are telling you what the original equipment was when your vehicle was new.  Sticking with the same rated tires is always a good idea.  If you don't know what you're doing, trying different sized tires and wheels can cause real issues when it comes to performance and safety, considering all the computerized systems now found on vehicles.  When in doubt, consult your service advisor when it comes to buying new tires.  He or she knows what those tire numbers and letters mean… and a whole lot more.

Tuffy Lake In The Hills
59 West Acorn Lane
Lake In The Hills, Illinois 60156
847-854-9850

More articles from Tuffy Lake in the Hills

Going (Lug) Nuts (Lug Nut Replacement)

June 29, 2025

Here's a part of your vehicle you probably don't think about much: lug nuts. They're what fasten your wheels onto your axles. Pretty important, right? In order to take the wheels off your vehicle to service the brakes, rotate the tires, etc., the lug nuts have to be in good shape so a wrench wi... More

Not-So-Smooth Operator (Transmission Signs of Trouble)

June 22, 2025

You are heading down a flat, newly paved street when all of a sudden you feel it. Your vehicle jumps a little bit when you're accelerating and changing gears. You know it's not the surface of the road because it's smooth as silk. So what did you just feel? That kind of jumpingor grinding or sl... More

Braking Good (Brake Drum Replacement)

June 15, 2025

Maybe your vehicle feels like Breaking Bad. In other words, when you brake, things are bad. You may find it takes you a longer distance to stop, you feel a vibration, or its pulsating when you depress the brake pedal, or perhaps your vehicle pulls to one side. Those can be symptoms of failing b... More