205/40R18 vs 235/40R18
235/40R18 is outside the ±3% rule as a replacement for 205/40R18: the diameter differs by +3.86%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 235/40R18 on a car calibrated for 205/40R18, the speedometer reads 57.8 mph when you're really doing 60, and the odometer under-counts by 3.9%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.2 mph |
| 45 mph | 46.7 mph |
| 60 mph | 62.3 mph |
| 70 mph | 72.7 mph |
| 80 mph | 83.1 mph |
Other sizes close to 205/40R18
- 205/40R18 vs 225/40R18+2.58%
- 205/40R18 vs 215/45R17+0.66%
- 205/40R18 vs 255/35R18+2.33%
- 205/40R18 vs 205/45R17-0.79%
- 205/40R18 vs 275/35R18+4.59%
- 205/40R18 vs 265/35R18+3.46%
- 205/40R18 vs 215/45R18+4.75%
- 205/40R18 vs 245/35R18+1.21%
- 205/40R18 vs 215/40R18+1.29%
- 205/40R18 vs 295/30R18+2.09%
- 205/40R18 vs 285/30R18+1.13%
- 205/40R18 vs 315/30R18+4.02%
Questions
Can I replace 205/40R18 with 235/40R18?
235/40R18 is outside the ±3% rule as a replacement for 205/40R18: the diameter differs by +3.86%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 205/40R18 and 235/40R18?
235/40R18 is 0.94" taller and 30 mm wider; the sidewall is +0.47". At an indicated 60 mph you'd actually be doing 62.3 mph.
Will 235/40R18 fit on 205/40R18 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.