315/75R17 vs 35x12.50R18

35x12.50R18 is 0.60 in (15.3 mm) shorter than 315/75R17, a −1.69% diameter difference. With the speedometer set for 315/75R17, an indicated 60 mph is 59.0 mph on 35x12.50R18.

Is this a safe swap?

Diameter difference −1.69%: within the ±3% guideline

By overall diameter alone, 35x12.50R18 falls inside the ±3% range commonly used as a guideline when replacing 315/75R17. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

Side profile and tread width, drawn to the same scale.

315/75R17 vs 35x12.50R18 differences
Measurement	315/75R17	35x12.50R18	Difference	% diff
Overall diameter	35.60 in (904.3 mm)	35.00 in (889.0 mm)	−0.60 in (−15.3 mm)	−1.69%
Sidewall height	9.30 in (236.3 mm)	8.50 in (215.9 mm)	−0.80 in (−20.3 mm)	−8.61%
Section width	12.40 in (315.0 mm)	12.50 in (317.5 mm)	+0.10 in (+2.5 mm)	+0.79%
Circumference	111.85 in (2,840.9 mm)	109.96 in (2,792.9 mm)	−1.89 in (−48.1 mm)	−1.69%
Revolutions per mile	566	576	+10	+1.72%

True speed with the speedometer calibrated for 315/75R17
Indicated	Actual on 315/75R17	Actual on 35x12.50R18	Difference
30 mph	30.0 mph	29.5 mph	−0.5 mph
60 mph	60.0 mph	59.0 mph	−1.0 mph
75 mph	75.0 mph	73.7 mph	−1.3 mph

Ride-height change: 35x12.50R18 lowers the vehicle by 0.30 in (7.6 mm) at the axle (half the −15.3 mm diameter difference).

35x12.50R18 is 0.60 in shorter than 315/75R17 and 3 mm wider, a 1.69% difference in overall diameter.

With the speedometer calibrated for 315/75R17, an indicated 60 mph is actually 59.0 mph on 35x12.50R18, and revolutions per mile change from 566 to 576.

35x12.50R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 315/75R17.

Size pages

Other comparisons with 315/75R17

Other comparisons with 35x12.50R18

Source: Calculated from standard tire geometry formulas. Verified 2026-09-27. How these numbers are calculated.