285/55R20 vs 33x12.50R20

33x12.50R20 is 0.66 in (16.7 mm) taller than 285/55R20, a +2.03% diameter difference. With the speedometer set for 285/55R20, an indicated 60 mph is 61.2 mph on 33x12.50R20.

Is this a safe swap?

Diameter difference +2.03%: within the ±3% guideline

By overall diameter alone, 33x12.50R20 falls inside the ±3% range commonly used as a guideline when replacing 285/55R20. 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.

285/55R20 vs 33x12.50R20 differences
Measurement	285/55R20	33x12.50R20	Difference	% diff
Overall diameter	32.34 in (821.5 mm)	33.00 in (838.2 mm)	+0.66 in (+16.7 mm)	+2.03%
Sidewall height	6.17 in (156.8 mm)	6.50 in (165.1 mm)	+0.33 in (+8.3 mm)	+5.33%
Section width	11.22 in (285.0 mm)	12.50 in (317.5 mm)	+1.28 in (+32.5 mm)	+11.40%
Circumference	101.61 in (2,580.8 mm)	103.67 in (2,633.3 mm)	+2.07 in (+52.5 mm)	+2.03%
Revolutions per mile	624	611	−12	−1.99%

True speed with the speedometer calibrated for 285/55R20
Indicated	Actual on 285/55R20	Actual on 33x12.50R20	Difference
30 mph	30.0 mph	30.6 mph	+0.6 mph
60 mph	60.0 mph	61.2 mph	+1.2 mph
75 mph	75.0 mph	76.5 mph	+1.5 mph

Ride-height change: 33x12.50R20 raises the vehicle by 0.33 in (8.4 mm) at the axle (half the +16.7 mm diameter difference).

33x12.50R20 is 0.66 in taller than 285/55R20 and 33 mm wider, a 2.03% difference in overall diameter.

With the speedometer calibrated for 285/55R20, an indicated 60 mph is actually 61.2 mph on 33x12.50R20, and revolutions per mile change from 624 to 611.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 285/55R20

Other comparisons with 33x12.50R20

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