285/60R18 vs 305/60R18
305/60R18 is outside the ±3% rule as a replacement for 285/60R18: the diameter differs by +3.00%, 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 285/60R18, the speedometer reads 58.3 mph when you're really doing 60, and the odometer under-counts by 3.0%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.9 mph |
| 45 mph | 46.4 mph |
| 60 mph | 61.8 mph |
| 70 mph | 72.1 mph |
| 80 mph | 82.4 mph |
Other sizes close to 285/60R18
- 285/60R18 vs 265/70R17+0.45%
- 285/60R18 vs 275/65R18+1.94%
- 285/60R18 vs 265/60R18-3.00%
- 285/60R18 vs 265/65R18+0.31%
- 285/60R18 vs 265/70R18+3.63%
- 285/60R18 vs 235/65R18-4.57%
- 285/60R18 vs 245/75R17+0.01%
- 285/60R18 vs 255/70R18+1.88%
- 285/60R18 vs 255/65R18-1.31%
- 285/60R18 vs 285/65R18+3.57%
- 285/60R18 vs 255/60R18-4.50%
- 285/60R18 vs 33x12.50R18+4.88%
Questions
Can I replace 285/60R18 with 305/60R18?
305/60R18 is outside the ±3% rule as a replacement for 285/60R18: the diameter differs by +3.00%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 285/60R18 and 305/60R18?
305/60R18 is 0.94" taller and 20 mm wider; the sidewall is +0.47". At an indicated 60 mph you'd actually be doing 61.8 mph.
Will 305/60R18 fit on 285/60R18 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.