255/40R17 vs 255/45R17
255/45R17 is outside the ±3% rule as a replacement for 255/40R17: the diameter differs by +4.01%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 255/45R17 on a car calibrated for 255/40R17, the speedometer reads 57.7 mph when you're really doing 60, and the odometer under-counts by 4.0%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.2 mph |
| 45 mph | 46.8 mph |
| 60 mph | 62.4 mph |
| 70 mph | 72.8 mph |
| 80 mph | 83.2 mph |
Other sizes close to 255/40R17
- 255/40R17 vs 225/45R17-0.24%
- 255/40R17 vs 225/40R18+0.22%
- 255/40R17 vs 225/50R17+3.30%
- 255/40R17 vs 205/55R16-0.61%
- 255/40R17 vs 215/45R17-1.65%
- 255/40R17 vs 205/50R17+0.16%
- 255/40R17 vs 215/50R17+1.73%
- 255/40R17 vs 235/45R17+1.18%
- 255/40R17 vs 245/45R17+2.60%
- 255/40R17 vs 255/35R18-0.02%
- 255/40R17 vs 245/40R17-1.26%
- 255/40R17 vs 205/45R17-3.07%
Questions
Can I replace 255/40R17 with 255/45R17?
255/45R17 is outside the ±3% rule as a replacement for 255/40R17: the diameter differs by +4.01%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 255/40R17 and 255/45R17?
255/45R17 is 1.00" taller and 0 mm wider; the sidewall is +0.50". At an indicated 60 mph you'd actually be doing 62.4 mph.
Will 255/45R17 fit on 255/40R17 wheels?
Both use a 17" rim, so the wheel diameter matches; check the wheel's width range for a 255 mm tire and the fender clearance.