275/70R17 vs 305/60R18
305/60R18 is a safe swap for 275/70R17 by the usual ±3% rule: the diameter differs by +0.78%.
Speedometer and odometer
With 305/60R18 on a car calibrated for 275/70R17, the speedometer reads 59.5 mph when you're really doing 60, and the odometer under-counts by 0.8%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.2 mph |
| 45 mph | 45.4 mph |
| 60 mph | 60.5 mph |
| 70 mph | 70.5 mph |
| 80 mph | 80.6 mph |
Other sizes close to 275/70R17
- 275/70R17 vs 265/70R17-1.71%
- 275/70R17 vs 275/65R18-0.26%
- 275/70R17 vs 285/70R17+1.71%
- 275/70R17 vs 245/75R17-2.14%
- 275/70R17 vs 265/65R17-4.96%
- 275/70R17 vs 235/80R17-1.10%
- 275/70R17 vs 255/70R18-0.32%
- 275/70R17 vs 255/70R17-3.43%
- 275/70R17 vs 255/75R17-0.31%
- 275/70R17 vs 295/70R17+3.43%
- 275/70R17 vs 235/75R17-3.98%
- 275/70R17 vs 33x12.50R17+2.62%
Questions
Can I replace 275/70R17 with 305/60R18?
305/60R18 is a safe swap for 275/70R17 by the usual ±3% rule: the diameter differs by +0.78%.
What's the difference between 275/70R17 and 305/60R18?
305/60R18 is 0.25" taller and 30 mm wider; the sidewall is -0.37". At an indicated 60 mph you'd actually be doing 60.5 mph.
Will 305/60R18 fit on 275/70R17 wheels?
No — 275/70R17 needs a 17" wheel and 305/60R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.