How to Read a Tire Size
Understand width, aspect ratio, wheel diameter, load index and speed rating before comparing tire sizes.
Start with the three size numbers
In 225/65 R17, 225 is the nominal section width in millimetres. The sidewall height is 65 percent of that width. R describes radial construction, and 17 is the wheel bead-seat diameter in inches. The wheel diameter is not the overall tire diameter.
Read beyond the size
The load index and speed rating are separate markings. Matching width, aspect ratio and rim diameter alone is not enough to approve a replacement. Use the vehicle placard and manufacturer documentation for accepted sizes and ratings.
Pressure comes from the vehicle
Use the specified cold pressure for the vehicle, axle and load condition. A maximum pressure printed on the tire sidewall is not the recommended everyday inflation pressure for your car.
Compare carefully
Our calculator compares nominal geometry. It cannot check suspension clearance, brake clearance, wheel offset, stability-control compatibility or legal approval. Confirm these separately before changing size.