245/35R20 vs 255/40R20
255/40R20 is outside the ±3% rule as a replacement for 245/35R20: the diameter differs by +4.78%, 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 245/35R20, the speedometer reads 57.3 mph when you're really doing 60, and the odometer under-counts by 4.8%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.4 mph |
| 45 mph | 47.2 mph |
| 60 mph | 62.9 mph |
| 70 mph | 73.3 mph |
| 80 mph | 83.8 mph |
Other sizes close to 245/35R20
- 245/35R20 vs 245/40R19-0.13%
- 245/35R20 vs 245/40R20+3.61%
- 245/35R20 vs 275/35R19-0.65%
- 245/35R20 vs 255/35R20+1.03%
- 245/35R20 vs 275/35R20+3.09%
- 245/35R20 vs 225/45R19+0.82%
- 245/35R20 vs 285/35R19+0.38%
- 245/35R20 vs 285/35R20+4.12%
- 245/35R20 vs 285/30R20-0.07%
- 245/35R20 vs 275/30R20-0.96%
- 245/35R20 vs 265/35R20+2.06%
- 245/35R20 vs 235/35R20-1.03%
Questions
Can I replace 245/35R20 with 255/40R20?
255/40R20 is outside the ±3% rule as a replacement for 245/35R20: the diameter differs by +4.78%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 245/35R20 and 255/40R20?
255/40R20 is 1.28" taller and 10 mm wider; the sidewall is +0.64". At an indicated 60 mph you'd actually be doing 62.9 mph.
Will 255/40R20 fit on 245/35R20 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.