toolbox · 01
tire size calculator
compare sizes, check wheel fitment, work out offset and clearance, and convert metric ↔ flotation.
Size comparison
| Metric | 245/40R18 | 225/40R18 | Diff |
|---|---|---|---|
| Overall diameter | 25.7" / 653 mm | 25.1" / 637 mm | 2.45% |
| Wheel size | 18.0" / 457 mm | 18.0" / 457 mm | 0% |
| Sidewall height | 3.9" / 98 mm | 3.5" / 90 mm | 8.16% |
| Section width | 9.6" / 245 mm | 8.9" / 225 mm | 8.16% |
| Circumference | 80.8" / 2052 mm | 78.8" / 2002 mm | 2.45% |
| Revolutions / mile | 784.2 | 803.9 | 2.51% |
| Revolutions / km | 487.3 | 499.5 | 2.51% |
Speedometer reading
Cluster calibrated for 245/40R18. True ground speed with 225/40R18 fitted:
| Speedo says | 20 | 40 | 60 | 80 | 100 | 120 |
| Actually going | 19.5 | 39 | 58.5 | 78 | 97.6 | 117.1 |
245/40R1825.7" / 653 mm
225/40R1825.1" / 637 mm