275/30R20 vs 245/40R20
245/40R20 is outside the ±3% rule as a replacement for 275/30R20: the diameter differs by +4.61%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 245/40R20 on a car calibrated for 275/30R20, the speedometer reads 57.4 mph when you're really doing 60, and the odometer under-counts by 4.6%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.4 mph |
| 45 mph | 47.1 mph |
| 60 mph | 62.8 mph |
| 70 mph | 73.2 mph |
| 80 mph | 83.7 mph |
Other sizes close to 275/30R20
- 275/30R20 vs 245/40R19+0.83%
- 275/30R20 vs 235/40R19-0.36%
- 275/30R20 vs 275/35R19+0.31%
- 275/30R20 vs 245/35R20+0.97%
- 275/30R20 vs 255/35R20+2.01%
- 275/30R20 vs 275/35R20+4.09%
- 275/30R20 vs 265/35R19-0.73%
- 275/30R20 vs 285/30R20+0.89%
- 275/30R20 vs 265/35R20+3.05%
- 275/30R20 vs 235/35R20-0.07%
- 275/30R20 vs 295/30R20+1.78%
- 275/30R20 vs 305/30R20+2.67%
Questions
Can I replace 275/30R20 with 245/40R20?
245/40R20 is outside the ±3% rule as a replacement for 275/30R20: the diameter differs by +4.61%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 275/30R20 and 245/40R20?
245/40R20 is 1.22" taller and 30 mm narrower; the sidewall is +0.61". At an indicated 60 mph you'd actually be doing 62.8 mph.
Will 245/40R20 fit on 275/30R20 wheels?
Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 245 mm tire and the fender clearance.