185/60R15 vs 205/40R17
Switching from 185/60R15 to 205/40R17 decreases the overall diameter by 7.2 mm (1.2%). That is within the usual ±3% guideline.
| 185/60R15 | 205/40R17 | Difference (mm / revs) | |
|---|---|---|---|
| Section width | 185 mm | 205 mm | +20.0 |
| Sidewall height | 111.0 mm | 82.0 mm | -29.0 |
| Rim diameter | 381.0 mm | 431.8 mm | +50.8 |
| Overall diameter | 603.0 mm | 595.8 mm | -7.2 |
| Circumference | 1,894.4 mm | 1,871.8 mm | -22.6 |
| Revolutions | 528 per km | 534 per km | +6.0 |
Speedometer effect
With 205/40R17 fitted on a car calibrated for 185/60R15, the real speed when the speedometer shows:
| Speedometer shows | Actual speed |
|---|---|
| 50 km/h | 49.4 km/h |
| 80 km/h | 79.0 km/h |
| 100 km/h | 98.8 km/h |
| 120 km/h | 118.6 km/h |
Smaller tires make the speedometer read higher than the actual speed. 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 205 mm tire has a manufacturer-specified rim width range.
185/60R15 dimensions · 205/40R17 dimensions · Open in calculator