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!

More From Auffenberg CDJR

  • 2020 Dodge Journey Interior

    Looking for a new SUV in O'Fallon? There are lots on the market, but the Dodge Journey is a true standout. Any great SUV has an inviting cabin, and the Dodge Journey interior exemplifies comfort with its flexible, tech-heavy design. Auffenberg CDJR covers Dodge Journey seating, Dodge Journey cargo space, and more below! View Inventory Apply…

  • 2020 Jeep Cherokee MPG

    When Belleville drivers want an offroading SUV that’s also got style, they go for the 2020 Jeep Cherokee. However, when you choose the Cherokee over the competition, you’re not just getting a powerful SUV, you’re also getting a fuel efficient one! The 2020 Jeep Cherokee MPG offers you up to 26 mpg combined according to…

  • 2020 RAM 2500 Towing Capacity Information

    The RAM 1500 is one of the most beloved new light-duty trucks for sale in the Smithton and East St. Louis areas, but what if it doesn’t provide enough towing capacity for you? You can upgrade to the RAM 2500, of course! Just how much can the RAM 2500 tow? Up to 19,860 pounds when configured correctly…

Saved Vehicles


You don't have any saved vehicles!

Look for this link on your favorites:


Once you've saved some vehicles, you can view them here at any time.

Contact Us

(618) 622-4546

Call Now

176 Auto Court • O'Fallon, IL 62269

Get Directions

Today's Hours:

Open Today! Sales: 9am-6pm

Open Today! Service: 7am-6pm

Auffenberg CDJR 38.5964005, -89.958124.