305/30R20 vs 235/45R19
235/45R19 is a safe swap for 305/30R20 by the usual ±3% rule: the diameter differs by +0.45%.
Speedometer and odometer
With 235/45R19 on a car calibrated for 305/30R20, the speedometer reads 59.7 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 | 60.3 mph |
| 70 mph | 70.3 mph |
| 80 mph | 80.4 mph |
Other sizes close to 305/30R20
- 305/30R20 vs 255/40R19-0.64%
- 305/30R20 vs 245/40R20+1.88%
- 305/30R20 vs 245/35R20-1.66%
- 305/30R20 vs 255/35R20-0.65%
- 305/30R20 vs 275/35R20+1.37%
- 305/30R20 vs 255/40R20+3.04%
- 305/30R20 vs 225/45R19-0.85%
- 305/30R20 vs 285/35R20+2.39%
- 305/30R20 vs 285/30R20-1.74%
- 305/30R20 vs 275/30R20-2.60%
- 305/30R20 vs 265/35R20+0.36%
- 305/30R20 vs 235/35R20-2.68%
Questions
Can I replace 305/30R20 with 235/45R19?
235/45R19 is a safe swap for 305/30R20 by the usual ±3% rule: the diameter differs by +0.45%.
What's the difference between 305/30R20 and 235/45R19?
235/45R19 is 0.12" taller and 70 mm narrower; the sidewall is +0.56". At an indicated 60 mph you'd actually be doing 60.3 mph.
Will 235/45R19 fit on 305/30R20 wheels?
No — 305/30R20 needs a 20" wheel and 235/45R19 a 19" wheel. This is a plus/minus-size swap that changes wheels too.