315/75R16 vs 35x12.50R18

35x12.50R18 is 0.40 in (10.1 mm) taller than 315/75R16, a +1.15% diameter difference. With the speedometer set for 315/75R16, an indicated 60 mph is 60.7 mph on 35x12.50R18.

Is this a safe swap?

Diameter difference +1.15%: within the ±3% guideline

By overall diameter alone, 35x12.50R18 falls inside the ±3% range commonly used as a guideline when replacing 315/75R16. 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.

315/75R16 vs 35x12.50R18 differences
Measurement	315/75R16	35x12.50R18	Difference	% diff
Overall diameter	34.60 in (878.9 mm)	35.00 in (889.0 mm)	+0.40 in (+10.1 mm)	+1.15%
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	108.71 in (2,761.1 mm)	109.96 in (2,792.9 mm)	+1.25 in (+31.7 mm)	+1.15%
Revolutions per mile	583	576	−7	−1.14%

True speed with the speedometer calibrated for 315/75R16
Indicated	Actual on 315/75R16	Actual on 35x12.50R18	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.7 mph	+0.7 mph
75 mph	75.0 mph	75.9 mph	+0.9 mph

Ride-height change: 35x12.50R18 raises the vehicle by 0.20 in (5.1 mm) at the axle (half the +10.1 mm diameter difference).

35x12.50R18 is 0.40 in taller than 315/75R16 and 3 mm wider, a 1.15% difference in overall diameter.

With the speedometer calibrated for 315/75R16, an indicated 60 mph is actually 60.7 mph on 35x12.50R18, and revolutions per mile change from 583 to 576.

35x12.50R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 315/75R16.

Size pages

Other comparisons with 315/75R16

Other comparisons with 35x12.50R18

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