315/75R16 vs 315/70R18

315/70R18 is 0.76 in (19.3 mm) taller than 315/75R16, a +2.20% diameter difference. With the speedometer set for 315/75R16, an indicated 60 mph is 61.3 mph on 315/70R18.

Is this a safe swap?

Diameter difference +2.20%: within the ±3% guideline

By overall diameter alone, 315/70R18 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 315/70R18 differences
Measurement	315/75R16	315/70R18	Difference	% diff
Overall diameter	34.60 in (878.9 mm)	35.36 in (898.2 mm)	+0.76 in (+19.3 mm)	+2.20%
Sidewall height	9.30 in (236.3 mm)	8.68 in (220.5 mm)	−0.62 in (−15.7 mm)	−6.67%
Section width	12.40 in (315.0 mm)	12.40 in (315.0 mm)	0.00 in (0.0 mm)	0.00%
Circumference	108.71 in (2,761.1 mm)	111.09 in (2,821.8 mm)	+2.39 in (+60.6 mm)	+2.20%
Revolutions per mile	583	570	−13	−2.15%

True speed with the speedometer calibrated for 315/75R16
Indicated	Actual on 315/75R16	Actual on 315/70R18	Difference
30 mph	30.0 mph	30.7 mph	+0.7 mph
60 mph	60.0 mph	61.3 mph	+1.3 mph
75 mph	75.0 mph	76.6 mph	+1.6 mph

Ride-height change: 315/70R18 raises the vehicle by 0.38 in (9.7 mm) at the axle (half the +19.3 mm diameter difference).

315/70R18 is 0.76 in taller than 315/75R16 and the same width, a 2.20% difference in overall diameter.

With the speedometer calibrated for 315/75R16, an indicated 60 mph is actually 61.3 mph on 315/70R18, and revolutions per mile change from 583 to 570.

315/70R18 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 315/70R18

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