275/40R21 vs 285/40R21
285/40R21 is a safe swap for 275/40R21 by the usual ±3% rule: the diameter differs by +1.06%.
Speedometer and odometer
With 285/40R21 on a car calibrated for 275/40R21, the speedometer reads 59.4 mph when you're really doing 60, and the odometer under-counts by 1.1%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.3 mph |
| 45 mph | 45.5 mph |
| 60 mph | 60.6 mph |
| 70 mph | 70.7 mph |
| 80 mph | 80.8 mph |
Other sizes close to 275/40R21
- 275/40R21 vs 245/50R20-0.05%
- 275/40R21 vs 275/45R20+0.28%
- 275/40R21 vs 265/45R20-0.92%
- 275/40R21 vs 265/40R21-1.06%
- 275/40R21 vs 275/35R21-3.65%
- 275/40R21 vs 295/35R21-1.79%
- 275/40R21 vs 275/45R21+3.65%
- 275/40R21 vs 255/40R21-2.12%
- 275/40R21 vs 265/35R21-4.58%
- 275/40R21 vs 285/35R22+0.65%
- 275/40R21 vs 295/40R21+2.12%
- 275/40R21 vs 285/45R21+4.84%
Questions
Can I replace 275/40R21 with 285/40R21?
285/40R21 is a safe swap for 275/40R21 by the usual ±3% rule: the diameter differs by +1.06%.
What's the difference between 275/40R21 and 285/40R21?
285/40R21 is 0.31" taller and 10 mm wider; the sidewall is +0.16". At an indicated 60 mph you'd actually be doing 60.6 mph.
Will 285/40R21 fit on 275/40R21 wheels?
Both use a 21" rim, so the wheel diameter matches; check the wheel's width range for a 285 mm tire and the fender clearance.