255/30R20 vs 305/30R19
305/30R19 is a safe swap for 255/30R20 by the usual ±3% rule: the diameter differs by +0.70%.
Speedometer and odometer
With 305/30R19 on a car calibrated for 255/30R20, 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 | 80.6 mph |
Other sizes close to 255/30R20
- 255/30R20 vs 255/35R19+0.02%
- 255/30R20 vs 245/35R20+2.80%
- 255/30R20 vs 255/35R20+3.86%
- 255/30R20 vs 225/40R19+0.24%
- 255/30R20 vs 285/30R20+2.72%
- 255/30R20 vs 275/30R20+1.82%
- 255/30R20 vs 265/35R20+4.92%
- 255/30R20 vs 235/35R20+1.74%
- 255/30R20 vs 295/30R20+3.63%
- 255/30R20 vs 305/30R20+4.54%
- 255/30R20 vs 295/30R19-0.21%
- 255/30R20 vs 245/30R20-0.91%
Questions
Can I replace 255/30R20 with 305/30R19?
305/30R19 is a safe swap for 255/30R20 by the usual ±3% rule: the diameter differs by +0.70%.
What's the difference between 255/30R20 and 305/30R19?
305/30R19 is 0.18" taller and 50 mm wider; the sidewall is +0.59". At an indicated 60 mph you'd actually be doing 60.4 mph.
Will 305/30R19 fit on 255/30R20 wheels?
No — 255/30R20 needs a 20" wheel and 305/30R19 a 19" wheel. This is a plus/minus-size swap that changes wheels too.