295/30R21 vs 245/40R21
245/40R21 is a safe swap for 295/30R21 by the usual ±3% rule: the diameter differs by +2.67%.
Speedometer and odometer
With 245/40R21 on a car calibrated for 295/30R21, the speedometer reads 58.4 mph when you're really doing 60, and the odometer under-counts by 2.7%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.8 mph |
| 45 mph | 46.2 mph |
| 60 mph | 61.6 mph |
| 70 mph | 71.9 mph |
| 80 mph | 82.1 mph |
Other sizes close to 295/30R21
- 295/30R21 vs 245/40R20-0.90%
- 295/30R21 vs 255/40R20+0.23%
- 295/30R21 vs 285/35R20-0.41%
- 295/30R21 vs 265/40R21+4.93%
- 295/30R21 vs 275/35R21+2.18%
- 295/30R21 vs 295/35R21+4.15%
- 295/30R21 vs 255/40R21+3.80%
- 295/30R21 vs 265/35R21+1.20%
- 295/30R21 vs 295/35R20+0.58%
- 295/30R21 vs 245/35R21-0.77%
- 295/30R21 vs 325/30R21+2.53%
- 295/30R21 vs 255/35R21+0.21%
Questions
Can I replace 295/30R21 with 245/40R21?
245/40R21 is a safe swap for 295/30R21 by the usual ±3% rule: the diameter differs by +2.67%.
What's the difference between 295/30R21 and 245/40R21?
245/40R21 is 0.75" taller and 50 mm narrower; the sidewall is +0.37". At an indicated 60 mph you'd actually be doing 61.6 mph.
Will 245/40R21 fit on 295/30R21 wheels?
Both use a 21" rim, so the wheel diameter matches; check the wheel's width range for a 245 mm tire and the fender clearance.