Enter both size codes
Use width, aspect ratio, and rim diameter as separate fields.
Width · profile · rim · speed
Compare tire sizes without hiding the assumptions.
TireCalc derives exact nominal diameters from metric radial size fields, labels pi-based outputs as approximate, and keeps fitment decisions outside the calculator.
All size and speed values stay in this browser. No account, vehicle lookup, upload, or backend.
Three transparent steps
Read, compare, verify
Inspect signed differences
See exact diameter and ratio before approximate circumference.
Verify real fitment elsewhere
Use the placard, manual, manufacturer, rules, and a professional.
Focused geometry
Useful before a real fitment check
- Compare nominal outside diameters.
- Estimate radius and clearance change.
- See theoretical speedometer ratio.
- Keep legal and safety decisions separate.
Compare nominal geometry
Check two tire sizes transparently
Enter width, aspect ratio, rim diameter, and one indicated speed. TireCalc keeps exact ratios local and labels real-world limits.