255/65R18 vs 305/60R18
305/60R18 is outside the ±3% rule as a replacement for 255/65R18: the diameter differs by +4.37%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 305/60R18 on a car calibrated for 255/65R18, the speedometer reads 57.5 mph when you're really doing 60, and the odometer under-counts by 4.4%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.3 mph |
| 45 mph | 47.0 mph |
| 60 mph | 62.6 mph |
| 70 mph | 73.1 mph |
| 80 mph | 83.5 mph |
Other sizes close to 255/65R18
- 255/65R18 vs 275/65R18+3.30%
- 255/65R18 vs 265/60R18-1.71%
- 255/65R18 vs 245/60R18-4.75%
- 255/65R18 vs 265/65R18+1.65%
- 255/65R18 vs 235/65R18-3.30%
- 255/65R18 vs 255/70R18+3.23%
- 255/65R18 vs 255/60R19-0.01%
- 255/65R18 vs 285/65R18+4.94%
- 255/65R18 vs 255/70R17+0.01%
- 255/65R18 vs 255/60R18-3.23%
- 255/65R18 vs 235/75R17-0.56%
- 255/65R18 vs 285/60R18+1.33%
Questions
Can I replace 255/65R18 with 305/60R18?
305/60R18 is outside the ±3% rule as a replacement for 255/65R18: the diameter differs by +4.37%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 255/65R18 and 305/60R18?
305/60R18 is 1.36" taller and 50 mm wider; the sidewall is +0.68". At an indicated 60 mph you'd actually be doing 62.6 mph.
Will 305/60R18 fit on 255/65R18 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.