255/35R18 vs 235/45R18
235/45R18 is outside the ±3% rule as a replacement for 255/35R18: the diameter differs by +5.19%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 235/45R18 on a car calibrated for 255/35R18, the speedometer reads 57.0 mph when you're really doing 60, and the odometer under-counts by 5.2%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.6 mph |
| 45 mph | 47.3 mph |
| 60 mph | 63.1 mph |
| 70 mph | 73.6 mph |
| 80 mph | 84.2 mph |
Other sizes close to 255/35R18
- 255/35R18 vs 225/45R17-0.22%
- 255/35R18 vs 245/40R18+2.75%
- 255/35R18 vs 225/45R18+3.78%
- 255/35R18 vs 225/40R18+0.24%
- 255/35R18 vs 205/50R17+0.17%
- 255/35R18 vs 235/40R18+1.49%
- 255/35R18 vs 255/40R18+4.01%
- 255/35R18 vs 275/35R18+2.20%
- 255/35R18 vs 265/35R18+1.10%
- 255/35R18 vs 255/40R17+0.02%
- 255/35R18 vs 215/45R18+2.36%
- 255/35R18 vs 245/35R18-1.10%
Questions
Can I replace 255/35R18 with 235/45R18?
235/45R18 is outside the ±3% rule as a replacement for 255/35R18: the diameter differs by +5.19%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 255/35R18 and 235/45R18?
235/45R18 is 1.30" taller and 20 mm narrower; the sidewall is +0.65". At an indicated 60 mph you'd actually be doing 63.1 mph.
Will 235/45R18 fit on 255/35R18 wheels?
Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 235 mm tire and the fender clearance.