305/70R16 vs 33x12.50R18

33x12.50R18 is 0.19 in (4.8 mm) taller than 305/70R16, a +0.58% diameter difference. With the speedometer set for 305/70R16, an indicated 60 mph is 60.3 mph on 33x12.50R18.

Is this a safe swap?

Diameter difference +0.58%: under 1%

By overall diameter alone, 33x12.50R18 is a near match for 305/70R16; the speedometer changes by less than 1%. 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.

305/70R16 vs 33x12.50R18 differences
Measurement	305/70R16	33x12.50R18	Difference	% diff
Overall diameter	32.81 in (833.4 mm)	33.00 in (838.2 mm)	+0.19 in (+4.8 mm)	+0.58%
Sidewall height	8.41 in (213.5 mm)	7.50 in (190.5 mm)	−0.91 in (−23.0 mm)	−10.77%
Section width	12.01 in (305.0 mm)	12.50 in (317.5 mm)	+0.49 in (+12.5 mm)	+4.10%
Circumference	103.08 in (2,618.2 mm)	103.67 in (2,633.3 mm)	+0.59 in (+15.1 mm)	+0.58%
Revolutions per mile	615	611	−4	−0.57%

True speed with the speedometer calibrated for 305/70R16
Indicated	Actual on 305/70R16	Actual on 33x12.50R18	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.3 mph	+0.3 mph
75 mph	75.0 mph	75.4 mph	+0.4 mph

Ride-height change: 33x12.50R18 raises the vehicle by 0.09 in (2.4 mm) at the axle (half the +4.8 mm diameter difference).

33x12.50R18 is 0.19 in taller than 305/70R16 and 13 mm wider, a 0.58% difference in overall diameter.

With the speedometer calibrated for 305/70R16, an indicated 60 mph is actually 60.3 mph on 33x12.50R18, and revolutions per mile change from 615 to 611.

33x12.50R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 305/70R16.

Size pages

Other comparisons with 305/70R16

Other comparisons with 33x12.50R18

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