305/65R18 vs 305/70R17
305/70R17 is a safe swap for 305/65R18 by the usual ±3% rule: the diameter differs by +0.60%.
Speedometer and odometer
With 305/70R17 on a car calibrated for 305/65R18, the speedometer reads 59.6 mph when you're really doing 60, and the odometer under-counts by 0.6%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.2 mph |
| 45 mph | 45.3 mph |
| 60 mph | 60.4 mph |
| 70 mph | 70.4 mph |
| 80 mph | 80.5 mph |
Other sizes close to 305/65R18
- 305/65R18 vs 275/65R18-4.57%
- 305/65R18 vs 275/70R18-1.35%
- 305/65R18 vs 265/70R18-2.99%
- 305/65R18 vs 255/70R18-4.63%
- 305/65R18 vs 35x12.50R18+4.13%
- 305/65R18 vs 285/65R18-3.05%
- 305/65R18 vs 295/70R18+1.93%
- 305/65R18 vs 33x12.50R18-1.82%
- 305/65R18 vs 285/75R17+0.66%
- 305/65R18 vs 285/75R18+3.63%
- 305/65R18 vs 325/65R18+3.05%
- 305/65R18 vs 305/70R18+3.57%
Questions
Can I replace 305/65R18 with 305/70R17?
305/70R17 is a safe swap for 305/65R18 by the usual ±3% rule: the diameter differs by +0.60%.
What's the difference between 305/65R18 and 305/70R17?
305/70R17 is 0.20" taller and 0 mm wider; the sidewall is +0.60". At an indicated 60 mph you'd actually be doing 60.4 mph.
Will 305/70R17 fit on 305/65R18 wheels?
No — 305/65R18 needs a 18" wheel and 305/70R17 a 17" wheel. This is a plus/minus-size swap that changes wheels too.