255/35R20 vs 255/40R20
255/40R20 is outside the ±3% rule as a replacement for 255/35R20: the diameter differs by +3.71%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 255/40R20 on a car calibrated for 255/35R20, the speedometer reads 57.9 mph when you're really doing 60, and the odometer under-counts by 3.7%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.1 mph |
| 45 mph | 46.7 mph |
| 60 mph | 62.2 mph |
| 70 mph | 72.6 mph |
| 80 mph | 83.0 mph |
Other sizes close to 255/35R20
- 255/35R20 vs 255/40R19+0.01%
- 255/35R20 vs 245/40R20+2.55%
- 255/35R20 vs 245/35R20-1.02%
- 255/35R20 vs 275/35R20+2.04%
- 255/35R20 vs 225/45R19-0.20%
- 255/35R20 vs 285/35R19-0.64%
- 255/35R20 vs 285/35R20+3.06%
- 255/35R20 vs 285/30R20-1.09%
- 255/35R20 vs 275/30R20-1.97%
- 255/35R20 vs 265/35R20+1.02%
- 255/35R20 vs 235/35R20-2.04%
- 255/35R20 vs 295/30R20-0.22%
Questions
Can I replace 255/35R20 with 255/40R20?
255/40R20 is outside the ±3% rule as a replacement for 255/35R20: the diameter differs by +3.71%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 255/35R20 and 255/40R20?
255/40R20 is 1.00" taller and 0 mm wider; the sidewall is +0.50". At an indicated 60 mph you'd actually be doing 62.2 mph.
Will 255/40R20 fit on 255/35R20 wheels?
Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 255 mm tire and the fender clearance.