245/75R17 vs 275/55R20
Switching from 245/75R17 to 275/55R20 increases the overall diameter by 11.2 mm (1.4%). That is within the usual ±3% guideline.
| 245/75R17 | 275/55R20 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 245 mm | 275 mm | +30.0 |
| Sidewall height | 183.8 mm | 151.2 mm | -32.6 |
| Rim diameter | 431.8 mm | 508.0 mm | +76.2 |
| Overall diameter | 799.3 mm | 810.5 mm | +11.2 |
| Circumference | 2,511.1 mm | 2,546.3 mm | +35.2 |
| Revolutions | 398 per km | 393 per km | -5.0 |
Speedometer effect
With 275/55R20 fitted on a car calibrated for 245/75R17, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 50.7 km/h |
| 80 km/h | 81.1 km/h |
| 100 km/h | 101.4 km/h |
| 120 km/h | 121.7 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 275 mm tire has a manufacturer-specified rim width range.
245/75R17 dimensions · 275/55R20 dimensions · Open in calculator