33x12.50R18 vs 275/60R20

275/60R20 is 0.01 in (0.2 mm) shorter than 33x12.50R18, a −0.02% diameter difference. With the speedometer set for 33x12.50R18, an indicated 60 mph is 60.0 mph on 275/60R20.

Is this a safe swap?

Diameter difference −0.02%: under 1%

By overall diameter alone, 275/60R20 is a near match for 33x12.50R18; 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.

33x12.50R18 vs 275/60R20 differences
Measurement	33x12.50R18	275/60R20	Difference	% diff
Overall diameter	33.00 in (838.2 mm)	32.99 in (838.0 mm)	−0.01 in (−0.2 mm)	−0.02%
Sidewall height	7.50 in (190.5 mm)	6.50 in (165.0 mm)	−1.00 in (−25.5 mm)	−13.39%
Section width	12.50 in (317.5 mm)	10.83 in (275.0 mm)	−1.67 in (−42.5 mm)	−13.39%
Circumference	103.67 in (2,633.3 mm)	103.65 in (2,632.7 mm)	−0.02 in (−0.6 mm)	−0.02%
Revolutions per mile	611	611	0	+0.02%

True speed with the speedometer calibrated for 33x12.50R18
Indicated	Actual on 33x12.50R18	Actual on 275/60R20
30 mph	30.0 mph	30.0 mph
60 mph	60.0 mph	60.0 mph
75 mph	75.0 mph	75.0 mph

Ride-height change: 275/60R20 lowers the vehicle by 0.00 in (0.1 mm) at the axle (half the −0.2 mm diameter difference).

275/60R20 is 0.01 in shorter than 33x12.50R18 and 43 mm narrower, a 0.02% difference in overall diameter.

With the speedometer calibrated for 33x12.50R18, an indicated 60 mph is actually 60.0 mph on 275/60R20, and revolutions per mile change from 611 to 611.

275/60R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 33x12.50R18.

Size pages

Other comparisons with 33x12.50R18

Other comparisons with 275/60R20

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