255/70R18 vs 305/65R18
305/65R18 is outside the ±3% rule as a replacement for 255/70R18: the diameter differs by +4.85%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 305/65R18 on a car calibrated for 255/70R18, the speedometer reads 57.2 mph when you're really doing 60, and the odometer under-counts by 4.9%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.5 mph |
| 45 mph | 47.2 mph |
| 60 mph | 62.9 mph |
| 70 mph | 73.4 mph |
| 80 mph | 83.9 mph |
Other sizes close to 255/70R18
- 255/70R18 vs 275/65R18+0.06%
- 255/70R18 vs 265/60R18-4.79%
- 255/70R18 vs 275/70R18+3.44%
- 255/70R18 vs 265/65R18-1.54%
- 255/70R18 vs 265/70R18+1.72%
- 255/70R18 vs 235/80R17-0.79%
- 255/70R18 vs 255/65R18-3.13%
- 255/70R18 vs 285/65R18+1.66%
- 255/70R18 vs 255/75R17+0.01%
- 255/70R18 vs 33x12.50R18+2.95%
- 255/70R18 vs 285/60R18-1.84%
- 255/70R18 vs 275/70R17+0.32%
Questions
Can I replace 255/70R18 with 305/65R18?
305/65R18 is outside the ±3% rule as a replacement for 255/70R18: the diameter differs by +4.85%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 255/70R18 and 305/65R18?
305/65R18 is 1.56" taller and 50 mm wider; the sidewall is +0.78". At an indicated 60 mph you'd actually be doing 62.9 mph.
Will 305/65R18 fit on 255/70R18 wheels?
Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 305 mm tire and the fender clearance.