275/35R20 vs 245/35R21
245/35R21 is a safe swap for 275/35R20 by the usual ±3% rule: the diameter differs by +0.63%.
Speedometer and odometer
With 245/35R21 on a car calibrated for 275/35R20, the speedometer reads 59.6 mph when you're really doing 60, and the odometer under-counts by 0.6%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.2 mph |
| 45 mph | 45.3 mph |
| 60 mph | 60.4 mph |
| 70 mph | 70.4 mph |
| 80 mph | 80.5 mph |
Other sizes close to 275/35R20
- 275/35R20 vs 245/45R19+0.37%
- 275/35R20 vs 245/45R20+4.00%
- 275/35R20 vs 275/40R20+3.93%
- 275/35R20 vs 245/40R20+0.50%
- 275/35R20 vs 275/40R19+0.30%
- 275/35R20 vs 245/35R20-3.00%
- 275/35R20 vs 255/35R20-2.00%
- 275/35R20 vs 255/40R20+1.64%
- 275/35R20 vs 235/45R19-0.91%
- 275/35R20 vs 285/35R20+1.00%
- 275/35R20 vs 315/35R20+4.00%
- 275/35R20 vs 285/30R20-3.07%
Questions
Can I replace 275/35R20 with 245/35R21?
245/35R21 is a safe swap for 275/35R20 by the usual ±3% rule: the diameter differs by +0.63%.
What's the difference between 275/35R20 and 245/35R21?
245/35R21 is 0.17" taller and 30 mm narrower; the sidewall is -0.41". At an indicated 60 mph you'd actually be doing 60.4 mph.
Will 245/35R21 fit on 275/35R20 wheels?
No — 275/35R20 needs a 20" wheel and 245/35R21 a 21" wheel. This is a plus/minus-size swap that changes wheels too.