285/40R21 vs 265/45R21
265/45R21 is a safe swap for 285/40R21 by the usual ±3% rule: the diameter differs by +1.38%.
Speedometer and odometer
With 265/45R21 on a car calibrated for 285/40R21, the speedometer reads 59.2 mph when you're really doing 60, and the odometer under-counts by 1.4%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.4 mph |
| 45 mph | 45.6 mph |
| 60 mph | 60.8 mph |
| 70 mph | 71.0 mph |
| 80 mph | 81.1 mph |
Other sizes close to 285/40R21
- 285/40R21 vs 255/50R20+0.21%
- 285/40R21 vs 275/45R20-0.77%
- 285/40R21 vs 235/55R20+0.67%
- 285/40R21 vs 265/40R21-2.10%
- 285/40R21 vs 275/35R21-4.66%
- 285/40R21 vs 295/35R21-2.82%
- 285/40R21 vs 275/45R21+2.56%
- 285/40R21 vs 255/40R21-3.15%
- 285/40R21 vs 285/35R22-0.41%
- 285/40R21 vs 295/40R21+1.05%
- 285/40R21 vs 285/45R21+3.74%
- 285/40R21 vs 325/30R21-4.33%
Questions
Can I replace 285/40R21 with 265/45R21?
265/45R21 is a safe swap for 285/40R21 by the usual ±3% rule: the diameter differs by +1.38%.
What's the difference between 285/40R21 and 265/45R21?
265/45R21 is 0.41" taller and 20 mm narrower; the sidewall is +0.21". At an indicated 60 mph you'd actually be doing 60.8 mph.
Will 265/45R21 fit on 285/40R21 wheels?
Both use a 21" rim, so the wheel diameter matches; check the wheel's width range for a 265 mm tire and the fender clearance.