255/35R20 vs 305/30R20
305/30R20 is a safe swap for 255/35R20 by the usual ±3% rule: the diameter differs by +0.66%.
Speedometer and odometer
With 305/30R20 on a car calibrated for 255/35R20, the speedometer reads 59.6 mph when you're really doing 60, and the odometer under-counts by 0.7%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.2 mph |
| 45 mph | 45.3 mph |
| 60 mph | 60.4 mph |
| 70 mph | 70.5 mph |
| 80 mph | 80.5 mph |
Other sizes close to 255/35R20
- 255/35R20 vs 255/40R19+0.01%
- 255/35R20 vs 245/40R20+2.55%
- 255/35R20 vs 245/35R20-1.02%
- 255/35R20 vs 275/35R20+2.04%
- 255/35R20 vs 255/40R20+3.71%
- 255/35R20 vs 225/45R19-0.20%
- 255/35R20 vs 285/35R19-0.64%
- 255/35R20 vs 285/35R20+3.06%
- 255/35R20 vs 285/30R20-1.09%
- 255/35R20 vs 275/30R20-1.97%
- 255/35R20 vs 265/35R20+1.02%
- 255/35R20 vs 235/35R20-2.04%
Questions
Can I replace 255/35R20 with 305/30R20?
305/30R20 is a safe swap for 255/35R20 by the usual ±3% rule: the diameter differs by +0.66%.
What's the difference between 255/35R20 and 305/30R20?
305/30R20 is 0.18" taller and 50 mm wider; the sidewall is +0.09". At an indicated 60 mph you'd actually be doing 60.4 mph.
Will 305/30R20 fit on 255/35R20 wheels?
Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 305 mm tire and the fender clearance.