275/65R18 vs 305/65R18
305/65R18 is outside the ±3% rule as a replacement for 275/65R18: the diameter differs by +4.79%, 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 275/65R18, the speedometer reads 57.3 mph when you're really doing 60, and the odometer under-counts by 4.8%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.4 mph |
| 45 mph | 47.2 mph |
| 60 mph | 62.9 mph |
| 70 mph | 73.4 mph |
| 80 mph | 83.8 mph |
Other sizes close to 275/65R18
- 275/65R18 vs 265/60R18-4.85%
- 275/65R18 vs 275/70R18+3.38%
- 275/65R18 vs 265/65R18-1.60%
- 275/65R18 vs 265/70R18+1.66%
- 275/65R18 vs 235/80R17-0.85%
- 275/65R18 vs 255/70R18-0.06%
- 275/65R18 vs 255/65R18-3.19%
- 275/65R18 vs 285/65R18+1.60%
- 275/65R18 vs 255/75R17-0.05%
- 275/65R18 vs 33x12.50R18+2.88%
- 275/65R18 vs 285/60R18-1.90%
- 275/65R18 vs 275/70R17+0.26%
Questions
Can I replace 275/65R18 with 305/65R18?
305/65R18 is outside the ±3% rule as a replacement for 275/65R18: the diameter differs by +4.79%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 275/65R18 and 305/65R18?
305/65R18 is 1.54" taller and 30 mm wider; the sidewall is +0.77". At an indicated 60 mph you'd actually be doing 62.9 mph.
Will 305/65R18 fit on 275/65R18 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.