295/40R21 vs 255/50R21
255/50R21 is a safe swap for 295/40R21 by the usual ±3% rule: the diameter differs by +2.47%.
Speedometer and odometer
With 255/50R21 on a car calibrated for 295/40R21, the speedometer reads 58.6 mph when you're really doing 60, and the odometer under-counts by 2.5%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.7 mph |
| 45 mph | 46.1 mph |
| 60 mph | 61.5 mph |
| 70 mph | 71.7 mph |
| 80 mph | 82.0 mph |
Other sizes close to 295/40R21
- 295/40R21 vs 255/50R20-0.83%
- 295/40R21 vs 265/50R20+0.47%
- 295/40R21 vs 235/55R20-0.38%
- 295/40R21 vs 265/40R21-3.12%
- 295/40R21 vs 295/35R21-3.83%
- 295/40R21 vs 275/45R21+1.49%
- 295/40R21 vs 265/40R22+0.18%
- 295/40R21 vs 255/40R21-4.16%
- 295/40R21 vs 285/45R21+2.66%
- 295/40R21 vs 265/45R21+0.32%
- 295/40R21 vs 285/40R21-1.04%
- 295/40R21 vs 275/40R21-2.08%
Questions
Can I replace 295/40R21 with 255/50R21?
255/50R21 is a safe swap for 295/40R21 by the usual ±3% rule: the diameter differs by +2.47%.
What's the difference between 295/40R21 and 255/50R21?
255/50R21 is 0.75" taller and 40 mm narrower; the sidewall is +0.37". At an indicated 60 mph you'd actually be doing 61.5 mph.
Will 255/50R21 fit on 295/40R21 wheels?
Both use a 21" rim, so the wheel diameter matches; check the wheel's width range for a 255 mm tire and the fender clearance.