275/35R21 vs 315/35R20
315/35R20 is a safe swap for 275/35R21 by the usual ±3% rule: the diameter differs by +0.36%.
Speedometer and odometer
With 315/35R20 on a car calibrated for 275/35R21, the speedometer reads 59.8 mph when you're really doing 60, and the odometer under-counts by 0.4%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.1 mph |
| 45 mph | 45.2 mph |
| 60 mph | 60.2 mph |
| 70 mph | 70.3 mph |
| 80 mph | 80.3 mph |
Other sizes close to 275/35R21
- 275/35R21 vs 245/45R20+0.36%
- 275/35R21 vs 275/40R20+0.29%
- 275/35R21 vs 265/40R21+2.69%
- 275/35R21 vs 295/35R21+1.93%
- 275/35R21 vs 255/40R21+1.58%
- 275/35R21 vs 265/35R21-0.96%
- 275/35R21 vs 245/35R21-2.89%
- 275/35R21 vs 305/35R20-0.61%
- 275/35R21 vs 285/40R21+4.89%
- 275/35R21 vs 325/30R21+0.34%
- 275/35R21 vs 275/40R21+3.79%
- 275/35R21 vs 235/45R20-0.88%
Questions
Can I replace 275/35R21 with 315/35R20?
315/35R20 is a safe swap for 275/35R21 by the usual ±3% rule: the diameter differs by +0.36%.
What's the difference between 275/35R21 and 315/35R20?
315/35R20 is 0.10" taller and 40 mm wider; the sidewall is +0.55". At an indicated 60 mph you'd actually be doing 60.2 mph.
Will 315/35R20 fit on 275/35R21 wheels?
No — 275/35R21 needs a 21" wheel and 315/35R20 a 20" wheel. This is a plus/minus-size swap that changes wheels too.