How it works
A walkthrough, end to end.
- 1
Enter the original tire size (e.g. 225/65R17).
- 2
Optionally enter a new tire size to compare.
- 3
See diameter, circumference, revs/mile, and speedometer error.
Reference
Tire size
Diameter (in) = wheel + 2 × (width × aspect/100) / 25.4. Circumference = π × diameter. Revs/mile = 63360 / circ.
Use cases
What you can do with this.
Plus-sizing
Check if larger wheels keep diameter close to stock.
Off-road tires
Compute speedometer error after a tire upgrade.
Lift kits
Confirm clearance with a bigger tire diameter.
Towing
Match tires for a trailer.
Winter swap
Verify dimensional match with summer tires.
FAQ
Frequently asked.
Width / aspect / wheel — e.g. 225/65R17 means 225mm wide, 65% sidewall ratio, 17" wheel.
If new tire is larger, speedo reads slow. Larger diameter means actual speed > displayed.
No. All math runs in your browser.
Same dimensional math; load rating differs.