305/30R19 vs 235/45R18
235/45R18 is a safe swap for 305/30R19 by the usual ±3% rule: the diameter differs by +0.47%.
Speedometer and odometer
With 235/45R18 on a car calibrated for 305/30R19, the speedometer reads 59.7 mph when you're really doing 60, and the odometer under-counts by 0.5%.
| 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 305/30R19
- 305/30R19 vs 225/45R18-0.89%
- 305/30R19 vs 245/40R19+1.95%
- 305/30R19 vs 235/40R19+0.75%
- 305/30R19 vs 255/40R19+3.16%
- 305/30R19 vs 255/35R19-0.68%
- 305/30R19 vs 255/40R18-0.66%
- 305/30R19 vs 275/35R19+1.43%
- 305/30R19 vs 245/35R19-1.73%
- 305/30R19 vs 225/40R19-0.45%
- 305/30R19 vs 235/35R19-2.78%
- 305/30R19 vs 225/45R19+2.93%
- 305/30R19 vs 285/35R19+2.48%
Questions
Can I replace 305/30R19 with 235/45R18?
235/45R18 is a safe swap for 305/30R19 by the usual ±3% rule: the diameter differs by +0.47%.
What's the difference between 305/30R19 and 235/45R18?
235/45R18 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 235/45R18 fit on 305/30R19 wheels?
No — 305/30R19 needs a 19" wheel and 235/45R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.