How to Check Tire Size

Find the size your car needs and the size it has

For a passenger car, SUV or light pickup, we’d start at the door label because a previous owner may have changed the tires or wheels. A tire’s molded code describes the tire in front of you; the label describes the vehicle’s factory fitment.

1. Open the driver’s door and find the Tire and Loading Information label on its edge or jamb. Photograph the whole label so the front, rear and spare entries stay together. The NHTSA tire guide (opens in a new tab) identifies this label as a source for the vehicle’s tire size.
2. Copy the front and rear entries separately, including any prefix, load number, speed letter and load designation. If the label gives different front and rear sizes, keep each entry with its axle. You now have a specification for each road-tire position.

3. Read the molded size code on the outside sidewall of each road tire. Photograph the entire code, then label the photos front left, front right, rear left and rear right. Copy the letters and numbers after the wheel diameter too; a size that appears to match can have a different load or speed rating.
4. Record the spare separately. When all four road-tire codes are legible and tied to their positions, you can compare each one with its front or rear specification.

For a metric radial passenger tire, the molded code carries its category, dimensions, construction and service ratings.

Record P, LT or no prefix exactly as molded. Passenger and light-truck tires follow different load rules even when their dimensions match. Compare the load index and speed letter after the diameter to see whether a same-size tire meets the vehicle’s tire requirement.

With paired load indexes, the first number applies when the tire is used singly and the second when tires are paired at one wheel position. Two tires on opposite ends of an axle are not a dual-wheel assembly. A light-truck load-range letter describes a load and inflation category, not a literal ply count; copy the service description because the dimensions and load range alone do not give the exact load index.

The nearby DOT identification code, its manufacturing date and treadwear grades are separate markings, not extensions of the size code. MAX LOAD and MAX PRESS describe tire limits. For the vehicle’s operating pressure, use the door label; tire pressure for your car is a separate comparison.

Compare each tire with its place on the car

Compare the two front tires with the placard’s front entry, then do the same for the rear. Look at the prefix, width, aspect ratio, construction, wheel diameter, load index, speed rating and any required XL, HL or Reinforced marking. A vehicle can intentionally use different front and rear sizes, but its two normal road tires on the same axle should be the same size.

In the table’s worked comparison, the placard and sidewall agree on width, aspect ratio, radial construction and wheel diameter. The ratings do not. Load index 99 represents 1,709 pounds per tire, below the 1,874 pounds represented by 102; T is rated at 118 mph, below H at 130 mph. The 99T tire has lower load and speed ratings than the 102H requirement.

For a replacement, use the factory code for that axle: match its size, tire category and load marking, use at least its load index, and meet or exceed the vehicle maker’s speed rating. A higher tire load rating does not raise the vehicle’s allowable load.

A door placard can print the tire size without a load index or speed letter. If yours does, get those requirements from the owner’s manual or the vehicle maker’s factory tire information. The rating on an existing tire tells you what is installed now. Keep the front and rear entries separate while you fill in the missing details.

A different wheel diameter calls for a closer look at the vehicle’s factory wheel-and-tire options. Compare that factory record with the tire code and wheel diameter at every position. An alternative package still needs tire and wheel load capacity for the vehicle and clearance around the brakes, suspension and wheel wells.

If the code or door label is hard to read

Dirt and poor light can hide molded characters. If the placard is missing or illegible, find the factory tire specification and identify the tires now on the car.

1. Park the car. Clean a dirty sidewall with water and a soft cloth, then shine a flashlight or phone light across the raised lettering. Photograph the code from an angle and enlarge the image. A legible prefix, size and service description complete that tire’s record.
2. Inspect the other tires and label each position separately. Use those codes to decipher a faint character, then photograph the entire code at each position to record what is on each wheel. If damage has destroyed a code, stop using that tire as the ordering reference.
3. If the door label is missing or illegible, look for the tire specification in the owner’s manual. If the manual lacks it, look for the factory tire specification in the vehicle maker’s vehicle information using the VIN, model year and trim. Compare that record with the codes on the tires now on the car and read each wheel diameter before ordering.

A VIN identifies the factory configuration, so inspect the car’s wheels for later changes. Use the molded code for the full tire size, load index and speed rating; measurements of outside diameter and the wheel’s outer lip give only partial clues. If factory records conflict with the tires and wheels on the car, identify both before ordering.

Why the tire size differs from the label

For a mismatch, look for another wheel-and-tire package listed for your VIN and trim, factory front and rear differences, a compact temporary spare, or a replacement that conflicts with the factory record. Compare all four road-tire positions before choosing among those explanations. A sidewall that differs from one placard entry may match the entry for its own axle.

A compact spare is the limited exception to normal road-tire matching. A T at the start of its size identifies a temporary spare; its smaller size can save storage space. Keep it out of the road-tire comparison and do not copy its size when buying a regular tire.

Stop normal driving if a tire rubs.

A temporary spare can be used only within its own restrictions while the regular tire is restored. For a compact spare, use no more than 50 mph, reach service as soon as possible, and follow any distance limit printed on the spare or in the vehicle instructions. Driving on a spare tire covers that temporary trip.

What correcting the size can cost

An ordinary passenger-car tire costs $100 to $250 and mounting and balancing adds $15 to $50 per tire, putting one installed tire at $120 to $300. Disposal, taxes, tire-pressure-monitoring parts and alignment can add charges, so get an itemized out-the-door total.

Owner checking ends if factory records conflict with the fitted wheels, a tire category or rating remains uncertain, or a tire rubs, is visibly damaged, has too little load capacity or unexpectedly differs from its axle mate. Contact a qualified tire shop or the vehicle dealer for a fitment identification; use roadside assistance or a tow if the car cannot be driven safely. Give them the VIN, year and trim, placard and sidewall photos labeled by position, and any rubbing or spare-tire use. Have them identify the tires and wheels before they quote the replacement.

Questions that come up before you buy