275/65R20 vs 315/70R17
Switching from 275/65R20 to 315/70R17 increases the overall diameter by 7.3 mm (0.8%). That is within the usual ±3% guideline.
| 275/65R20 | 315/70R17 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 275 mm | 315 mm | +40.0 |
| Sidewall height | 178.8 mm | 220.5 mm | +41.7 |
| Rim diameter | 508.0 mm | 431.8 mm | -76.2 |
| Overall diameter | 865.5 mm | 872.8 mm | +7.3 |
| Circumference | 2,719.0 mm | 2,742.0 mm | +23.0 |
| Revolutions | 368 per km | 365 per km | -3.0 |
Speedometer effect
With 315/70R17 fitted on a car calibrated for 275/65R20, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 50.4 km/h |
| 80 km/h | 80.7 km/h |
| 100 km/h | 100.8 km/h |
| 120 km/h | 121.0 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 315 mm tire has a manufacturer-specified rim width range.
275/65R20 dimensions · 315/70R17 dimensions · Open in calculator