225/60R17 vs 245/40R20
Switching from 225/60R17 to 245/40R20 increases the overall diameter by 2.2 mm (0.3%). That is within the usual ±3% guideline.
| 225/60R17 | 245/40R20 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 225 mm | 245 mm | +20.0 |
| Sidewall height | 135.0 mm | 98.0 mm | -37.0 |
| Rim diameter | 431.8 mm | 508.0 mm | +76.2 |
| Overall diameter | 701.8 mm | 704.0 mm | +2.2 |
| Circumference | 2,204.8 mm | 2,211.7 mm | +6.9 |
| Revolutions | 454 per km | 452 per km | -2.0 |
Speedometer effect
With 245/40R20 fitted on a car calibrated for 225/60R17, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 50.2 km/h |
| 80 km/h | 80.3 km/h |
| 100 km/h | 100.3 km/h |
| 120 km/h | 120.4 km/h |
Larger tires make the car go faster than the speedometer shows. Most speedometers also read slightly high from the factory.
Before you change size
- Check the sizes approved for your vehicle on the door-jamb placard or in the owner's manual.
- Check clearance to suspension, brakes and arches at full lock and full compression.
- Match or exceed the original load index and speed rating.
- Wider tires need an appropriate rim width; a 245 mm tire has a manufacturer-specified rim width range.
225/60R17 dimensions · 245/40R20 dimensions · Open in calculator