255/40R20 vs 265/35R21
265/35R21 is a safe swap for 255/40R20 by the usual ±3% rule: the diameter differs by +0.97%.
Speedometer and odometer
With 265/35R21 on a car calibrated for 255/40R20, the speedometer reads 59.4 mph when you're really doing 60, and the odometer under-counts by 1.0%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.3 mph |
| 45 mph | 45.4 mph |
| 60 mph | 60.6 mph |
| 70 mph | 70.7 mph |
| 80 mph | 80.8 mph |
Other sizes close to 255/40R20
- 255/40R20 vs 245/45R20+2.32%
- 255/40R20 vs 255/45R20+3.58%
- 255/40R20 vs 275/40R20+2.25%
- 255/40R20 vs 245/40R20-1.12%
- 255/40R20 vs 255/45R19+0.01%
- 255/40R20 vs 245/35R20-4.56%
- 255/40R20 vs 255/35R20-3.58%
- 255/40R20 vs 275/35R20-1.62%
- 255/40R20 vs 235/50R19+0.79%
- 255/40R20 vs 265/45R20+4.85%
- 255/40R20 vs 285/35R20-0.63%
- 255/40R20 vs 315/35R20+2.32%
Questions
Can I replace 255/40R20 with 265/35R21?
265/35R21 is a safe swap for 255/40R20 by the usual ±3% rule: the diameter differs by +0.97%.
What's the difference between 255/40R20 and 265/35R21?
265/35R21 is 0.27" taller and 10 mm wider; the sidewall is -0.36". At an indicated 60 mph you'd actually be doing 60.6 mph.
Will 265/35R21 fit on 255/40R20 wheels?
No — 255/40R20 needs a 20" wheel and 265/35R21 a 21" wheel. This is a plus/minus-size swap that changes wheels too.