255/40R17 vs 235/45R17
235/45R17 is a safe swap for 255/40R17 by the usual ±3% rule: the diameter differs by +1.18%.
Speedometer and odometer
With 235/45R17 on a car calibrated for 255/40R17, the speedometer reads 59.3 mph when you're really doing 60, and the odometer under-counts by 1.2%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.4 mph |
| 45 mph | 45.5 mph |
| 60 mph | 60.7 mph |
| 70 mph | 70.8 mph |
| 80 mph | 80.9 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 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%
- 255/40R17 vs 235/50R17+4.88%
Questions
Can I replace 255/40R17 with 235/45R17?
235/45R17 is a safe swap for 255/40R17 by the usual ±3% rule: the diameter differs by +1.18%.
What's the difference between 255/40R17 and 235/45R17?
235/45R17 is 0.30" taller and 20 mm narrower; the sidewall is +0.15". At an indicated 60 mph you'd actually be doing 60.7 mph.
Will 235/45R17 fit on 255/40R17 wheels?
Both use a 17" rim, so the wheel diameter matches; check the wheel's width range for a 235 mm tire and the fender clearance.