Gypes

Metric tire comparison

Tire size calculator

Compare two P-metric tire sizes, including diameter, sidewall, circumference, revolutions, clearance, and estimated speedometer change.

Copy the whole size instead of splitting it into six fields. Find a code such as 225/65R17 on each tire sidewall or manufacturer specification. The speed field appears after both codes are recognized.

1Copy the current and proposed sizes

Use P-metric radial sizes. A P or LT prefix and a trailing load/speed description such as 102H are accepted.

How metric tire size math works

For a size such as 225/65R17, 225 is the nominal section width in millimeters, 65 means each sidewall is 65% of that width, and 17 is the wheel diameter in inches. The calculated unloaded diameter is wheel diameter plus two sidewalls after converting millimeters to inches. Circumference is diameter multiplied by π, and theoretical revolutions are travel distance divided by circumference.

The input accepts ordinary P-metric radial forms such as 225/65R17, P225/65R17, LT235/60R18, or 225/65R17 102H. It intentionally stops on flotation sizes such as 33×12.50R15 and motorcycle, temporary-spare, bias-ply, or incomplete specifications because those formats need different assumptions.

Speedometer and clearance estimates

With no calibration change, estimated actual speed equals indicated speed multiplied by new diameter divided by current diameter. A larger tire travels farther per revolution and generally makes the vehicle move faster than indicated. Approximate ride-height change is half the diameter difference. These values are geometric estimates, not direct measurements.

Nominal dimensions are not guaranteed dimensions

Mounted dimensions vary by manufacturer, model, load, inflation pressure, approved measuring-rim width, tread depth, construction, and production tolerance. Real rolling circumference also changes under load. Compare the exact manufacturer specification sheet for both tires rather than relying only on the sidewall designation.

Fitment requires more than diameter

A similar diameter does not prove safe fitment. Confirm wheel width and diameter, load index, speed rating, tire type, axle requirements, bolt pattern, offset, center bore, brake and suspension clearance, fender clearance through full steering and suspension travel, TPMS compatibility, and applicable vehicle or legal limits. All-wheel-drive systems can have strict circumference-matching requirements.

Do not choose or install a tire from this calculator alone. Use the vehicle placard and owner’s manual, the tire and wheel manufacturers’ approved specifications, and a qualified tire professional. Recalibration may be required after a size change.