255/45R21 vs 295/40R21
295/40R21 is a safe swap for 255/45R21 by the usual ±3% rule: the diameter differs by +0.85%.
Speedometer and odometer
With 295/40R21 on a car calibrated for 255/45R21, the speedometer reads 59.5 mph when you're really doing 60, and the odometer under-counts by 0.9%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.3 mph |
| 45 mph | 45.4 mph |
| 60 mph | 60.5 mph |
| 70 mph | 70.6 mph |
| 80 mph | 80.7 mph |
Other sizes close to 255/45R21
- 255/45R21 vs 255/50R20+0.01%
- 255/45R21 vs 275/45R20-0.97%
- 255/45R21 vs 235/55R20+0.47%
- 255/45R21 vs 265/40R21-2.29%
- 255/45R21 vs 275/35R21-4.85%
- 255/45R21 vs 295/35R21-3.01%
- 255/45R21 vs 275/45R21+2.36%
- 255/45R21 vs 255/40R21-3.34%
- 255/45R21 vs 285/35R22-0.60%
- 255/45R21 vs 285/45R21+3.54%
- 255/45R21 vs 285/40R21-0.20%
- 255/45R21 vs 265/45R21+1.18%
Questions
Can I replace 255/45R21 with 295/40R21?
295/40R21 is a safe swap for 255/45R21 by the usual ±3% rule: the diameter differs by +0.85%.
What's the difference between 255/45R21 and 295/40R21?
295/40R21 is 0.26" taller and 40 mm wider; the sidewall is +0.13". At an indicated 60 mph you'd actually be doing 60.5 mph.
Will 295/40R21 fit on 255/45R21 wheels?
Both use a 21" rim, so the wheel diameter matches; check the wheel's width range for a 295 mm tire and the fender clearance.