225/40R18 vs 235/40R18
235/40R18 is a safe swap for 225/40R18 by the usual ±3% rule: the diameter differs by +1.26%.
Speedometer and odometer
With 235/40R18 on a car calibrated for 225/40R18, the speedometer reads 59.3 mph when you're really doing 60, and the odometer under-counts by 1.3%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.4 mph |
| 45 mph | 45.6 mph |
| 60 mph | 60.8 mph |
| 70 mph | 70.9 mph |
| 80 mph | 81.0 mph |
Other sizes close to 225/40R18
- 225/40R18 vs 225/45R17-0.46%
- 225/40R18 vs 245/40R18+2.51%
- 225/40R18 vs 225/45R18+3.53%
- 225/40R18 vs 235/45R18+4.94%
- 225/40R18 vs 205/50R17-0.06%
- 225/40R18 vs 235/45R17+0.96%
- 225/40R18 vs 255/35R18-0.24%
- 225/40R18 vs 255/40R18+3.77%
- 225/40R18 vs 275/35R18+1.96%
- 225/40R18 vs 265/35R18+0.86%
- 225/40R18 vs 255/40R17-0.22%
- 225/40R18 vs 215/45R18+2.12%
Questions
Can I replace 225/40R18 with 235/40R18?
235/40R18 is a safe swap for 225/40R18 by the usual ±3% rule: the diameter differs by +1.26%.
What's the difference between 225/40R18 and 235/40R18?
235/40R18 is 0.31" taller and 10 mm wider; the sidewall is +0.16". At an indicated 60 mph you'd actually be doing 60.8 mph.
Will 235/40R18 fit on 225/40R18 wheels?
Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 235 mm tire and the fender clearance.