275/70R18 vs 305/70R18
305/70R18 is outside the ±3% rule as a replacement for 275/70R18: the diameter differs by +4.99%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 305/70R18 on a car calibrated for 275/70R18, the speedometer reads 57.1 mph when you're really doing 60, and the odometer under-counts by 5.0%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.5 mph |
| 45 mph | 47.2 mph |
| 60 mph | 63.0 mph |
| 70 mph | 73.5 mph |
| 80 mph | 84.0 mph |
Other sizes close to 275/70R18
- 275/70R18 vs 275/65R18-3.27%
- 275/70R18 vs 265/65R18-4.81%
- 275/70R18 vs 265/70R18-1.66%
- 275/70R18 vs 255/70R18-3.32%
- 275/70R18 vs 285/65R18-1.72%
- 275/70R18 vs 295/70R18+3.32%
- 275/70R18 vs 295/70R17+0.31%
- 275/70R18 vs 33x12.50R18-0.47%
- 275/70R18 vs 33x12.50R17-0.47%
- 275/70R18 vs 325/65R18+4.45%
- 275/70R18 vs 255/80R17-0.28%
- 275/70R18 vs 305/65R18+1.37%
Questions
Can I replace 275/70R18 with 305/70R18?
305/70R18 is outside the ±3% rule as a replacement for 275/70R18: the diameter differs by +4.99%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 275/70R18 and 305/70R18?
305/70R18 is 1.65" taller and 30 mm wider; the sidewall is +0.83". At an indicated 60 mph you'd actually be doing 63.0 mph.
Will 305/70R18 fit on 275/70R18 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.