265/40R21 vs 265/45R21
265/45R21 is outside the ±3% rule as a replacement for 265/40R21: the diameter differs by +3.56%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 265/45R21 on a car calibrated for 265/40R21, the speedometer reads 57.9 mph when you're really doing 60, and the odometer under-counts by 3.6%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.1 mph |
| 45 mph | 46.6 mph |
| 60 mph | 62.1 mph |
| 70 mph | 72.5 mph |
| 80 mph | 82.8 mph |
Other sizes close to 265/40R21
- 265/40R21 vs 265/45R20+0.15%
- 265/40R21 vs 275/35R21-2.62%
- 265/40R21 vs 295/35R21-0.74%
- 265/40R21 vs 275/45R21+4.76%
- 265/40R21 vs 255/40R21-1.07%
- 265/40R21 vs 265/35R21-3.56%
- 265/40R21 vs 265/35R22-0.15%
- 265/40R21 vs 295/40R20-0.19%
- 265/40R21 vs 295/40R21+3.22%
- 265/40R21 vs 285/40R21+2.15%
- 265/40R21 vs 325/30R21-2.28%
- 265/40R21 vs 235/50R20-0.32%
Questions
Can I replace 265/40R21 with 265/45R21?
265/45R21 is outside the ±3% rule as a replacement for 265/40R21: the diameter differs by +3.56%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 265/40R21 and 265/45R21?
265/45R21 is 1.04" taller and 0 mm wider; the sidewall is +0.52". At an indicated 60 mph you'd actually be doing 62.1 mph.
Will 265/45R21 fit on 265/40R21 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.