33x12.50R17 vs 285/70R18

285/70R18 is 0.71 in (18.0 mm) taller than 33x12.50R17, a +2.15% diameter difference. With the speedometer set for 33x12.50R17, an indicated 60 mph is 61.3 mph on 285/70R18.

Is this a safe swap?

Diameter difference +2.15%: within the ±3% guideline

By overall diameter alone, 285/70R18 falls inside the ±3% range commonly used as a guideline when replacing 33x12.50R17. 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.

33x12.50R17 vs 285/70R18 differences
Measurement	33x12.50R17	285/70R18	Difference	% diff
Overall diameter	33.00 in (838.2 mm)	33.71 in (856.2 mm)	+0.71 in (+18.0 mm)	+2.15%
Sidewall height	8.00 in (203.2 mm)	7.85 in (199.5 mm)	−0.15 in (−3.7 mm)	−1.82%
Section width	12.50 in (317.5 mm)	11.22 in (285.0 mm)	−1.28 in (−32.5 mm)	−10.24%
Circumference	103.67 in (2,633.3 mm)	105.90 in (2,689.8 mm)	+2.23 in (+56.5 mm)	+2.15%
Revolutions per mile	611	598	−13	−2.10%

True speed with the speedometer calibrated for 33x12.50R17
Indicated	Actual on 33x12.50R17	Actual on 285/70R18	Difference
30 mph	30.0 mph	30.6 mph	+0.6 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: 285/70R18 raises the vehicle by 0.35 in (9.0 mm) at the axle (half the +18.0 mm diameter difference).

285/70R18 is 0.71 in taller than 33x12.50R17 and 33 mm narrower, a 2.15% difference in overall diameter.

With the speedometer calibrated for 33x12.50R17, an indicated 60 mph is actually 61.3 mph on 285/70R18, and revolutions per mile change from 611 to 598.

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

Size pages

Other comparisons with 33x12.50R17

Other comparisons with 285/70R18

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