MIAMI TIRE NOTEBOOK

How to Read a Tire Size Before You Request Options

That string on the sidewall is useful information. It is not, on its own, a recommendation for what to buy next.

Find the vehicle’s reference first

The driver’s door-area tire information placard and owner’s manual are the best starting points. The tires currently installed could differ from the original specification, especially on a used car or one with aftermarket wheels. NHTSA advises replacing tires with the original size or another size recommended by the vehicle manufacturer.

If you cannot safely read the tire or find the placard, leave the size blank on the inquiry form and share the vehicle year, make and model instead. Do not crawl into traffic or move an unsafe vehicle to find a marking.

Decode an example: 225/45R18

In this example, 225 is the nominal section width in millimeters. The 45 is the aspect ratio: sidewall height expressed as a percentage of section width, not a height in millimeters. R identifies radial construction. The 18 is the rim diameter in inches. This example is educational; it is not a suggested size for your vehicle.

Additional letters and numbers can identify tire type, load index and speed rating. XL, LT, run-flat and other markings can matter to the specification. Ask a professional to interpret the full marking rather than replacing only the most recognizable part.

Check front and rear separately

Some vehicles use a staggered setup with different tire sizes on the front and rear axles. Record both if that applies. All-wheel-drive vehicles may also have manufacturer-specific matching requirements; do not assume a single tire can be replaced independently without checking the manual and a qualified shop’s assessment.

Size is not inflation pressure

The pressure molded into a tire sidewall is not the vehicle’s recommended everyday cold inflation pressure. Use the vehicle placard or owner’s manual. NHTSA defines a cold tire for this check as one not driven for at least three hours. Front and rear pressures may differ on some vehicles, so follow the actual label rather than a generic number online.

What to put in a useful inquiry

Share the complete size you can read, plus the vehicle year, make and model if known. Mention different front and rear sizes or changed wheels. A tire professional still needs to confirm fitment, ratings, condition and the work required. Our form does not need your VIN, registration number or a photo of documents.