335/30R18 vs 255/45R18
255/45R18 is outside the ±3% rule as a replacement for 335/30R18: the diameter differs by +4.33%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 255/45R18 on a car calibrated for 335/30R18, the speedometer reads 57.5 mph when you're really doing 60, and the odometer under-counts by 4.3%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.3 mph |
| 45 mph | 46.9 mph |
| 60 mph | 62.6 mph |
| 70 mph | 73.0 mph |
| 80 mph | 83.5 mph |
Other sizes close to 335/30R18
- 335/30R18 vs 225/45R18+0.23%
- 335/30R18 vs 245/40R18-0.76%
- 335/30R18 vs 225/40R18-3.19%
- 335/30R18 vs 225/50R17-0.21%
- 335/30R18 vs 245/45R18+2.96%
- 335/30R18 vs 235/45R18+1.60%
- 335/30R18 vs 235/40R18-1.98%
- 335/30R18 vs 225/50R18+3.65%
- 335/30R18 vs 245/45R17-0.90%
- 335/30R18 vs 255/35R19+0.44%
- 335/30R18 vs 255/35R18-3.42%
- 335/30R18 vs 255/40R18+0.46%
Questions
Can I replace 335/30R18 with 255/45R18?
255/45R18 is outside the ±3% rule as a replacement for 335/30R18: the diameter differs by +4.33%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 335/30R18 and 255/45R18?
255/45R18 is 1.12" taller and 80 mm narrower; the sidewall is +0.56". At an indicated 60 mph you'd actually be doing 62.6 mph.
Will 255/45R18 fit on 335/30R18 wheels?
Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 255 mm tire and the fender clearance.