235/80R17 vs 255/70R18
255/70R18 is a safe swap for 235/80R17 by the usual ±3% rule: the diameter differs by +0.79%.
Speedometer and odometer
With 255/70R18 on a car calibrated for 235/80R17, the speedometer reads 59.5 mph when you're really doing 60, and the odometer under-counts by 0.8%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.2 mph |
| 45 mph | 45.4 mph |
| 60 mph | 60.5 mph |
| 70 mph | 70.6 mph |
| 80 mph | 80.6 mph |
Other sizes close to 235/80R17
- 235/80R17 vs 265/70R17-0.62%
- 235/80R17 vs 275/65R18+0.85%
- 235/80R17 vs 265/75R16-0.48%
- 235/80R17 vs 245/70R17-4.09%
- 235/80R17 vs 285/70R17+2.85%
- 235/80R17 vs 265/65R18-0.76%
- 235/80R17 vs 245/75R17-1.05%
- 235/80R17 vs 265/65R17-3.90%
- 235/80R17 vs 235/85R16-0.24%
- 235/80R17 vs 255/70R17-2.35%
- 235/80R17 vs 255/75R17+0.80%
- 235/80R17 vs 295/70R17+4.58%
Questions
Can I replace 235/80R17 with 255/70R18?
255/70R18 is a safe swap for 235/80R17 by the usual ±3% rule: the diameter differs by +0.79%.
What's the difference between 235/80R17 and 255/70R18?
255/70R18 is 0.25" taller and 20 mm wider; the sidewall is -0.37". At an indicated 60 mph you'd actually be doing 60.5 mph.
Will 255/70R18 fit on 235/80R17 wheels?
No — 235/80R17 needs a 17" wheel and 255/70R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.