295/40R21 vs 315/40R21
315/40R21 is a safe swap for 295/40R21 by the usual ±3% rule: the diameter differs by +2.08%.
Speedometer and odometer
With 315/40R21 on a car calibrated for 295/40R21, the speedometer reads 58.8 mph when you're really doing 60, and the odometer under-counts by 2.1%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.6 mph |
| 45 mph | 45.9 mph |
| 60 mph | 61.2 mph |
| 70 mph | 71.5 mph |
| 80 mph | 81.7 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 315/40R21?
315/40R21 is a safe swap for 295/40R21 by the usual ±3% rule: the diameter differs by +2.08%.
What's the difference between 295/40R21 and 315/40R21?
315/40R21 is 0.63" taller and 20 mm wider; the sidewall is +0.31". At an indicated 60 mph you'd actually be doing 61.2 mph.
Will 315/40R21 fit on 295/40R21 wheels?
Both use a 21" rim, so the wheel diameter matches; check the wheel's width range for a 315 mm tire and the fender clearance.