305/70R18 vs 35x12.50R18
35x12.50R18 is a safe swap for 305/70R18 by the usual ±3% rule: the diameter differs by +0.54%.
Side by side
| 305/70R18 | 35x12.50R18 | Difference | |
|---|---|---|---|
| Overall diameter | 34.81" | 35.00" | +0.19" (+0.54%) |
| Section width | 305 mm | 318 mm | +13 mm |
| Sidewall | 8.41" | 8.50" | +0.09" |
| Rim | 18" | 18" | same |
| Circumference | 109.4" | 110.0" | +0.6" |
| Revs per mile | 579 | 576 | -3 |
| Ride height | — | — | +0.09" |
| Speedometer reads 60 mph | 60.0 | 60.3 | +0.3 mph |
Speedometer and odometer
With 35x12.50R18 on a car calibrated for 305/70R18, the speedometer reads 59.7 mph when you're really doing 60, and the odometer under-counts by 0.5%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.2 mph |
| 45 mph | 45.2 mph |
| 60 mph | 60.3 mph |
| 70 mph | 70.4 mph |
| 80 mph | 80.4 mph |
Other sizes close to 305/70R18
Questions
Can I replace 305/70R18 with 35x12.50R18?
35x12.50R18 is a safe swap for 305/70R18 by the usual ±3% rule: the diameter differs by +0.54%.
What's the difference between 305/70R18 and 35x12.50R18?
35x12.50R18 is 0.19" taller and 13 mm wider; the sidewall is +0.09". At an indicated 60 mph you'd actually be doing 60.3 mph.
Will 35x12.50R18 fit on 305/70R18 wheels?
Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 318 mm tire and the fender clearance.