255/35R18 vs 315/30R18
315/30R18 is a safe swap for 255/35R18 by the usual ±3% rule: the diameter differs by +1.65%.
Speedometer and odometer
With 315/30R18 on a car calibrated for 255/35R18, the speedometer reads 59.0 mph when you're really doing 60, and the odometer under-counts by 1.7%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.5 mph |
| 45 mph | 45.7 mph |
| 60 mph | 61.0 mph |
| 70 mph | 71.2 mph |
| 80 mph | 81.3 mph |
Other sizes close to 255/35R18
- 255/35R18 vs 225/45R17-0.22%
- 255/35R18 vs 245/40R18+2.75%
- 255/35R18 vs 225/45R18+3.78%
- 255/35R18 vs 225/40R18+0.24%
- 255/35R18 vs 205/50R17+0.17%
- 255/35R18 vs 235/40R18+1.49%
- 255/35R18 vs 255/40R18+4.01%
- 255/35R18 vs 275/35R18+2.20%
- 255/35R18 vs 265/35R18+1.10%
- 255/35R18 vs 255/40R17+0.02%
- 255/35R18 vs 215/45R18+2.36%
- 255/35R18 vs 245/35R18-1.10%
Questions
Can I replace 255/35R18 with 315/30R18?
315/30R18 is a safe swap for 255/35R18 by the usual ±3% rule: the diameter differs by +1.65%.
What's the difference between 255/35R18 and 315/30R18?
315/30R18 is 0.41" taller and 60 mm wider; the sidewall is +0.21". At an indicated 60 mph you'd actually be doing 61.0 mph.
Will 315/30R18 fit on 255/35R18 wheels?
Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 315 mm tire and the fender clearance.