Tire Size Comparison Calculator
Compare old and new tire diameters and speedometer error.
Calculate tire size comparison calculator from clear inputs
Tire Size Comparison Calculator gives a focused worksheet for home & diy questions where a quick deterministic estimate is more useful than a spreadsheet. The tire size comparison calculator fields mirror the variables in its formula, and the output separates the main result from supporting values so you can sanity-check this calculation before reusing it.
Changing from 26.3 to 27.6 inch tires makes a 60 mph indicated speed about 62.9658 mph actual.
Keep the estimate private in your browser
For Tire Size Comparison Calculator, every calculation runs in your browser with no upload, account, cookie, live lookup, or server-side storage. The tire size comparison calculator result is best treated as a planning number because the real-world constraints behind this estimate can change the answer. Adjust the tire size comparison calculator assumptions and confirm important decisions against the relevant source of truth for that exact situation.
Frequently Asked Questions
How do I get the diameter from a tire size?
Wheel size + 2 × (width × aspect ratio ÷ 100) ÷ 25.4. A 225/65R17 tire is 17 + 2 × (225 × 0.65) ÷ 25.4, about 28.5 inches.
How is speedometer error calculated?
By the ratio of the new diameter to the old. Going from 26.3 to 27.6 inches is about 4.9% larger, so an indicated 60 mph is really about 63 mph.
How big a size change is safe?
Many fitters keep the overall diameter within about 3% of the original to avoid speedometer, ABS, and transmission issues. Check clearance and load rating too.
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