305/50R20 vs 33x12.50R20

33x12.50R20 is 0.99 in (25.2 mm) taller than 305/50R20, a +3.10% diameter difference. With the speedometer set for 305/50R20, an indicated 60 mph is 61.9 mph on 33x12.50R20.

Is this a safe swap?

Diameter difference +3.10%: outside the ±3% guideline

By overall diameter alone, 33x12.50R20 falls outside the ±3% range commonly used as a guideline when replacing 305/50R20; speedometer and ride-height changes are larger. 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.

305/50R20 vs 33x12.50R20 differences
Measurement	305/50R20	33x12.50R20	Difference	% diff
Overall diameter	32.01 in (813.0 mm)	33.00 in (838.2 mm)	+0.99 in (+25.2 mm)	+3.10%
Sidewall height	6.00 in (152.5 mm)	6.50 in (165.1 mm)	+0.50 in (+12.6 mm)	+8.26%
Section width	12.01 in (305.0 mm)	12.50 in (317.5 mm)	+0.49 in (+12.5 mm)	+4.10%
Circumference	100.56 in (2,554.1 mm)	103.67 in (2,633.3 mm)	+3.12 in (+79.2 mm)	+3.10%
Revolutions per mile	630	611	−19	−3.01%

True speed with the speedometer calibrated for 305/50R20
Indicated	Actual on 305/50R20	Actual on 33x12.50R20	Difference
30 mph	30.0 mph	30.9 mph	+0.9 mph
60 mph	60.0 mph	61.9 mph	+1.9 mph
75 mph	75.0 mph	77.3 mph	+2.3 mph

Ride-height change: 33x12.50R20 raises the vehicle by 0.50 in (12.6 mm) at the axle (half the +25.2 mm diameter difference).

33x12.50R20 is 0.99 in taller than 305/50R20 and 13 mm wider, a 3.10% difference in overall diameter.

With the speedometer calibrated for 305/50R20, an indicated 60 mph is actually 61.9 mph on 33x12.50R20, and revolutions per mile change from 630 to 611.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 305/50R20

Other comparisons with 33x12.50R20

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