285/70R17 vs 33x12.50R18

33x12.50R18 is 0.29 in (7.4 mm) taller than 285/70R17, a +0.89% diameter difference. With the speedometer set for 285/70R17, an indicated 60 mph is 60.5 mph on 33x12.50R18.

Is this a safe swap?

Diameter difference +0.89%: under 1%

By overall diameter alone, 33x12.50R18 is a near match for 285/70R17; 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.

285/70R17 vs 33x12.50R18 differences
Measurement	285/70R17	33x12.50R18	Difference	% diff
Overall diameter	32.71 in (830.8 mm)	33.00 in (838.2 mm)	+0.29 in (+7.4 mm)	+0.89%
Sidewall height	7.85 in (199.5 mm)	7.50 in (190.5 mm)	−0.35 in (−9.0 mm)	−4.51%
Section width	11.22 in (285.0 mm)	12.50 in (317.5 mm)	+1.28 in (+32.5 mm)	+11.40%
Circumference	102.76 in (2,610.0 mm)	103.67 in (2,633.3 mm)	+0.92 in (+23.2 mm)	+0.89%
Revolutions per mile	617	611	−5	−0.88%

True speed with the speedometer calibrated for 285/70R17
Indicated	Actual on 285/70R17	Actual on 33x12.50R18	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.5 mph	+0.5 mph
75 mph	75.0 mph	75.7 mph	+0.7 mph

Ride-height change: 33x12.50R18 raises the vehicle by 0.15 in (3.7 mm) at the axle (half the +7.4 mm diameter difference).

33x12.50R18 is 0.29 in taller than 285/70R17 and 33 mm wider, a 0.89% difference in overall diameter.

With the speedometer calibrated for 285/70R17, an indicated 60 mph is actually 60.5 mph on 33x12.50R18, and revolutions per mile change from 617 to 611.

33x12.50R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 285/70R17.

Size pages

Other comparisons with 285/70R17

Other comparisons with 33x12.50R18

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