305/30R19 vs 235/40R19
235/40R19 is a safe swap for 305/30R19 by the usual ±3% rule: the diameter differs by +0.75%.
Speedometer and odometer
With 235/40R19 on a car calibrated for 305/30R19, the speedometer reads 59.6 mph when you're really doing 60, and the odometer under-counts by 0.8%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.2 mph |
| 45 mph | 45.3 mph |
| 60 mph | 60.5 mph |
| 70 mph | 70.5 mph |
| 80 mph | 80.6 mph |
Other sizes close to 305/30R19
- 305/30R19 vs 225/45R18-0.89%
- 305/30R19 vs 235/45R18+0.47%
- 305/30R19 vs 245/40R19+1.95%
- 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 235/40R19?
235/40R19 is a safe swap for 305/30R19 by the usual ±3% rule: the diameter differs by +0.75%.
What's the difference between 305/30R19 and 235/40R19?
235/40R19 is 0.20" taller and 70 mm narrower; the sidewall is +0.10". At an indicated 60 mph you'd actually be doing 60.5 mph.
Will 235/40R19 fit on 305/30R19 wheels?
Both use a 19" rim, so the wheel diameter matches; check the wheel's width range for a 235 mm tire and the fender clearance.