255/35R21 vs 265/40R21
265/40R21 is outside the ±3% rule as a replacement for 255/35R21: the diameter differs by +4.71%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 265/40R21 on a car calibrated for 255/35R21, the speedometer reads 57.3 mph when you're really doing 60, and the odometer under-counts by 4.7%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.4 mph |
| 45 mph | 47.1 mph |
| 60 mph | 62.8 mph |
| 70 mph | 73.3 mph |
| 80 mph | 83.8 mph |
Other sizes close to 255/35R21
- 255/35R21 vs 255/40R20+0.01%
- 255/35R21 vs 285/35R20-0.62%
- 255/35R21 vs 275/35R21+1.97%
- 255/35R21 vs 295/35R21+3.93%
- 255/35R21 vs 255/40R21+3.58%
- 255/35R21 vs 265/35R21+0.98%
- 255/35R21 vs 295/35R20+0.37%
- 255/35R21 vs 245/35R21-0.98%
- 255/35R21 vs 325/30R21+2.32%
- 255/35R21 vs 315/30R21+1.47%
- 255/35R21 vs 285/35R21+2.95%
- 255/35R21 vs 245/40R21+2.46%
Questions
Can I replace 255/35R21 with 265/40R21?
265/40R21 is outside the ±3% rule as a replacement for 255/35R21: the diameter differs by +4.71%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 255/35R21 and 265/40R21?
265/40R21 is 1.32" taller and 10 mm wider; the sidewall is +0.66". At an indicated 60 mph you'd actually be doing 62.8 mph.
Will 265/40R21 fit on 255/35R21 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.