235/45R18 vs 315/30R19
315/30R19 is a safe swap for 235/45R18 by the usual ±3% rule: the diameter differs by +0.43%.
Speedometer and odometer
With 315/30R19 on a car calibrated for 235/45R18, 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 | 80.3 mph |
Other sizes close to 235/45R18
- 235/45R18 vs 225/45R18-1.35%
- 235/45R18 vs 245/40R18-2.32%
- 235/45R18 vs 225/40R18-4.71%
- 235/45R18 vs 245/45R18+1.35%
- 235/45R18 vs 235/50R18+3.51%
- 235/45R18 vs 215/55R17-0.06%
- 235/45R18 vs 235/40R18-3.51%
- 235/45R18 vs 225/50R18+2.02%
- 235/45R18 vs 235/40R19+0.28%
- 235/45R18 vs 255/35R18-4.93%
- 235/45R18 vs 255/40R18-1.12%
- 235/45R18 vs 275/35R19+0.96%
Questions
Can I replace 235/45R18 with 315/30R19?
315/30R19 is a safe swap for 235/45R18 by the usual ±3% rule: the diameter differs by +0.43%.
What's the difference between 235/45R18 and 315/30R19?
315/30R19 is 0.11" taller and 80 mm wider; the sidewall is -0.44". At an indicated 60 mph you'd actually be doing 60.3 mph.
Will 315/30R19 fit on 235/45R18 wheels?
No — 235/45R18 needs a 18" wheel and 315/30R19 a 19" wheel. This is a plus/minus-size swap that changes wheels too.