Need new tires for your car but not sure how to read tire size? Learn about tire size and other vital specs.
How to Read the Size of a Tire
Updated on Nov. 07, 2024
Reading the Size of a Tire
Like most vehicle parts, tires eventually wear out and need replacement. Wear and tear of the treads reduces traction, and aging rubber makes the tires weaker and more susceptible to going flat. That’s why experts recommend replacing your tires every five or six years, even if the tire treads aren’t completely worn down.
“If you are a DIYer looking to replace your own tires, knowing how to read tire sizes is an essential skill,” says Duane “Doc” Watson, a technical trainer at Bosch Mobility Aftermarket. “You need to be able to accurately purchase the correct tires for your vehicle because failure to do so can have an impact on safety and overall performance.”
The type of tires you choose needs to be the right size and shape to fit onto your vehicle’s wheels and inside its wheel wells, with enough room for the suspension to work properly. Maximizing ease of handling also matters. That’s why size is the first important thing to get right. Then there’s tire type, speed rating and load index.
Sound confusing? Here’s a simple explanation of all important tire information, beginning with size.
Plus, here’s how to change a car tire:
These tips will make changing a tire easier and safer.
Finding Tire Size
Almost all modern tires have size specifications printed on them. Look for a prominent group of letters and numbers molded on your tire’s sidewall, or check your owner’s manual. Sometimes, the characters printed on tires are large and painted white for easy visibility. Other times they’re smaller and close to the inside edge of the tire, near the rim. Either way, look for a collection of letters and numbers resembling this: P185/60R14 82H. The specifics will vary, but the pattern is almost always the same.
What Do All Those Numbers and Letters Mean?
“The sidewall has a lot of information,” says Chris “Moose” Pyle, an auto expert with JustAnswer.com. “All those letters, numbers, symbols and warnings mean something.”
Concerning size, the primary parts to decode are the wheel diameter, tire height and tire width. Let’s use the tire specs P185/60R14 82H as an example:
- The number 185 is the tire’s width in millimeters, from one sidewall to the other.
- The number 60 after the forward-slash character means the tire’s height from rim to tread is 60 percent of its width, which again is 185 millimeters.
- R14 means the tire is meant to fit on a 14-in. diameter wheel.
Then, tire sidewalls also tell tales of max speed rating, load range (the maximum weight a tire can hold), how much air pressure they should contain, when they were manufactured and whether they’re snow-rated or tubeless tires. There are often also wear lugs on the treads, to clue you in to when it’s time to buy new tires, says Pyle.
Besides getting the correct size, it’s important to pay attention to many of these other specs as well when buying new tires, especially if you have a heavy duty truck or van, because with those it can be especially dangerous if you don’t get a tire with a high enough load capacity.
To decode those symbols, using our example from above:
- The P stands for “passenger,” meaning the tire is intended for passenger vehicles. It might also say LT for “light truck” or T for “temporary spare.”
- The R means it’s a radial construction tire, which refers to the direction of the tire’s internal structural cords. These days, radial tires are the industry standard for passenger vehicles.
- The 82H is the tire’s maximal load and speed rating. A tire with a load index of 82 can handle 1047 lbs. maximum. An H speed rating means the tire can sustain driving speeds up to 130 mph before the rubber starts to get damaged.
Consult your vehicle and tire manufacturers for a full range of tire load and speed indexes.
About the Experts
- Duane “Doc” Watson is a technical trainer at Bosch Mobility Aftermarket. He has more than 45 years of experience in automotive repair, has trained thousands of technicians and earned many industry awards, including Chevrolet Technician of the Year and Buick Service Master of the Year.
- Chris “Moose” Pyle is a master-certified technician with 20-plus years of automotive experience. He has also worked as an expert for JustAnswer.com since 2006, where he answers hundreds of car maintenance and repair questions a day.
Next, learn how to get a stuck tire off your vehicle.
