285/70R18 vs 305/70R17
305/70R17 is a safe swap for 285/70R18 by the usual ±3% rule: the diameter differs by +0.30%.
Speedometer and odometer
With 305/70R17 on a car calibrated for 285/70R18, the speedometer reads 59.8 mph when you're really doing 60, and the odometer under-counts by 0.3%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.1 mph |
| 45 mph | 45.1 mph |
| 60 mph | 60.2 mph |
| 70 mph | 70.2 mph |
| 80 mph | 80.2 mph |
Other sizes close to 285/70R18
- 285/70R18 vs 275/65R18-4.85%
- 285/70R18 vs 275/70R18-1.64%
- 285/70R18 vs 265/70R18-3.27%
- 285/70R18 vs 255/70R18-4.91%
- 285/70R18 vs 35x12.50R18+3.83%
- 285/70R18 vs 285/65R18-3.33%
- 285/70R18 vs 295/70R18+1.64%
- 285/70R18 vs 33x12.50R18-2.10%
- 285/70R18 vs 285/75R17+0.36%
- 285/70R18 vs 285/75R18+3.33%
- 285/70R18 vs 325/65R18+2.74%
- 285/70R18 vs 305/70R18+3.27%
Questions
Can I replace 285/70R18 with 305/70R17?
305/70R17 is a safe swap for 285/70R18 by the usual ±3% rule: the diameter differs by +0.30%.
What's the difference between 285/70R18 and 305/70R17?
305/70R17 is 0.10" taller and 20 mm wider; the sidewall is +0.55". At an indicated 60 mph you'd actually be doing 60.2 mph.
Will 305/70R17 fit on 285/70R18 wheels?
No — 285/70R18 needs a 18" wheel and 305/70R17 a 17" wheel. This is a plus/minus-size swap that changes wheels too.