285/65R18 vs 305/65R18
305/65R18 is outside the ±3% rule as a replacement for 285/65R18: the diameter differs by +3.14%, 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 285/65R18, the speedometer reads 58.2 mph when you're really doing 60, and the odometer under-counts by 3.1%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.9 mph |
| 45 mph | 46.4 mph |
| 60 mph | 61.9 mph |
| 70 mph | 72.2 mph |
| 80 mph | 82.5 mph |
Other sizes close to 285/65R18
- 285/65R18 vs 275/65R18-1.57%
- 285/65R18 vs 275/70R18+1.75%
- 285/65R18 vs 285/70R17+0.37%
- 285/65R18 vs 265/65R18-3.14%
- 285/65R18 vs 265/70R18+0.06%
- 285/65R18 vs 255/70R18-1.63%
- 285/65R18 vs 255/65R18-4.71%
- 285/65R18 vs 33x12.50R18+1.27%
- 285/65R18 vs 285/60R18-3.44%
- 285/65R18 vs 275/60R18-4.89%
- 285/65R18 vs 305/60R18-0.54%
- 285/65R18 vs 285/70R18+3.44%
Questions
Can I replace 285/65R18 with 305/65R18?
305/65R18 is outside the ±3% rule as a replacement for 285/65R18: the diameter differs by +3.14%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 285/65R18 and 305/65R18?
305/65R18 is 1.02" taller and 20 mm wider; the sidewall is +0.51". At an indicated 60 mph you'd actually be doing 61.9 mph.
Will 305/65R18 fit on 285/65R18 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.