What Do Tire Numbers Mean?

Row of Tires


If you’ve ever knelt down by the side of your car, holding an air pressure hose, trying to decipher the letters and numbers on the side of your tire, hoping to figure out how much air should go into it, this article is for you. The good news is that you don’t have to be a rocket scientist to understand what the numbers on tires mean. The helpful experts in our service department believe it’s important for Belleville drivers to understand every important tire number, meaning they will not only know how much air pressure to apply, but which size to select when it comes time to replace a tire. So, what do tire numbers mean? Let’s find out.

Tire Number Meaning: Air Pressure

What do tire numbers mean when they come before “PSI”? This is the air pressure to which you should inflate your tires. “PSI” is an acronym that stands for “Pounds per Square Inch”. Most air pressure machines at gas stations have a tire gauge that will tell you how much air pressure is in your tire. Even so, it’s a good idea to carry a gauge in your car. And the PSI is probably the most important number on their tires that Smithton drivers need to know. But, what do the other numbers on tires mean? Let’s talk about size.

Tire Number Meaning: Size

The biggest numbers on the tire are usually the ones that indicate size. They are usually formatted like “P225/50R16” or “225/50R16”. Here’s what those numbers on your tires mean:

  • Letter at the beginning
    • P – Passenger vehicle
    • T – Temporary spare
    • LT – Light truck
    • ST – Special trailer service
  • Number before the “/” – This is the section width of the tire in millimeters.
  • Number right after the “/” – This is the sidewall aspect ratio (sidewall height from rim to tread)
  • Letter after the sidewall aspect ratio – indicates internal construction of the tire
    • R – Radial
    • D – Diagonal or bias ply
    • B – Belted
  • Number after the internal construction letter – rim size in inches
Stack of Tires

The Service Department at Auffenberg CDJR in O'Fallon is Here to Help

Not only do our tire experts know what tire numbers mean, they know exactly which kind of tire is right for the conditions you drive in. And we take the hassle out of getting your car serviced. You can even schedule service online. We’re just a short drive away from East St. Louis, but feel free to contact us today!

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176 Auto Court • O'Fallon, IL 62269

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Auffenberg CDJR 38.5964005, -89.958124.