205/40R18 vs 255/35R18
255/35R18 is a safe swap for 205/40R18 by the usual ±3% rule: the diameter differs by +2.33%.
Speedometer and odometer
With 255/35R18 on a car calibrated for 205/40R18, the speedometer reads 58.6 mph when you're really doing 60, and the odometer under-counts by 2.3%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.7 mph |
| 45 mph | 46.1 mph |
| 60 mph | 61.4 mph |
| 70 mph | 71.6 mph |
| 80 mph | 81.9 mph |
Other sizes close to 205/40R18
- 205/40R18 vs 225/40R18+2.58%
- 205/40R18 vs 215/45R17+0.66%
- 205/40R18 vs 235/40R18+3.86%
- 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 255/35R18?
255/35R18 is a safe swap for 205/40R18 by the usual ±3% rule: the diameter differs by +2.33%.
What's the difference between 205/40R18 and 255/35R18?
255/35R18 is 0.57" taller and 50 mm wider; the sidewall is +0.29". At an indicated 60 mph you'd actually be doing 61.4 mph.
Will 255/35R18 fit on 205/40R18 wheels?
Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 255 mm tire and the fender clearance.