Tire Size Calculator

Stay within 3% of the original tire diameter. Larger differences can affect speedometer accuracy, ABS/traction control calibration, and may cause rubbing on wheel wells. A 3% change equals about 1 mph speedometer error at 30 mph.

Example: 225/65R17. 225 = width in mm. 65 = aspect ratio (sidewall height as % of width). R = radial construction. 17 = rim diameter in inches. The overall diameter depends on all three numbers.

Yes. Larger diameter tires cause your speedometer to read slower than actual speed. For example, going from 225/65R17 to 235/70R17 increases diameter by about 3.5%, meaning at an indicated 60 mph you are actually going about 62 mph.

The Tire Size Calculator is an online tool that lets you compare tire sizes with diameter difference, speedometer error, and clearance changes. It is part of NexTool's collection of free tools designed to help you work faster and more efficiently.

Using the Tire Size Calculator is simple: visit the tool page, enter your data or input into the provided fields, and get instant results. Follow the controls on the page. Some functions require sign-in or a paid plan; see Pricing for limits.

The Free plan includes 10 tool uses per day. Some features require an account or a paid plan. Check the controls on the tool page and Pricing for the applicable limits.

The Tire Size Calculator returns results based on the inputs and the tool methodology. Check assumptions, units and source dates. Treat projections as estimates. For critical decisions, always consult a qualified professional.

Yes, the Tire Size Calculator is fully responsive and works perfectly on smartphones, tablets, and desktop computers. Simply open NexTool in your mobile browser and navigate to the tool — no app download required.