245/40R21 vs 265/40R21
265/40R21 is a safe swap for 245/40R21 by the usual ±3% rule: the diameter differs by +2.19%.
Speedometer and odometer
With 265/40R21 on a car calibrated for 245/40R21, the speedometer reads 58.7 mph when you're really doing 60, and the odometer under-counts by 2.2%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.7 mph |
| 45 mph | 46.0 mph |
| 60 mph | 61.3 mph |
| 70 mph | 71.5 mph |
| 80 mph | 81.8 mph |
Other sizes close to 245/40R21
- 245/40R21 vs 245/45R20-0.12%
- 245/40R21 vs 275/40R20-0.19%
- 245/40R21 vs 315/35R20-0.12%
- 245/40R21 vs 275/35R21-0.48%
- 245/40R21 vs 295/35R21+1.44%
- 245/40R21 vs 255/40R21+1.10%
- 245/40R21 vs 265/35R21-1.44%
- 245/40R21 vs 245/35R21-3.36%
- 245/40R21 vs 285/40R21+4.39%
- 245/40R21 vs 285/40R20+0.90%
- 245/40R21 vs 325/30R21-0.14%
- 245/40R21 vs 275/40R21+3.29%
Questions
Can I replace 245/40R21 with 265/40R21?
265/40R21 is a safe swap for 245/40R21 by the usual ±3% rule: the diameter differs by +2.19%.
What's the difference between 245/40R21 and 265/40R21?
265/40R21 is 0.63" taller and 20 mm wider; the sidewall is +0.31". At an indicated 60 mph you'd actually be doing 61.3 mph.
Will 265/40R21 fit on 245/40R21 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.