265/70R18 vs 33x12.50R20

33x12.50R20 is 0.39 in (10.0 mm) taller than 265/70R18, a +1.21% diameter difference. With the speedometer set for 265/70R18, an indicated 60 mph is 60.7 mph on 33x12.50R20.

Is this a safe swap?

Diameter difference +1.21%: within the ±3% guideline

By overall diameter alone, 33x12.50R20 falls inside the ±3% range commonly used as a guideline when replacing 265/70R18. 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.

265/70R18 vs 33x12.50R20 differences
Measurement	265/70R18	33x12.50R20	Difference	% diff
Overall diameter	32.61 in (828.2 mm)	33.00 in (838.2 mm)	+0.39 in (+10.0 mm)	+1.21%
Sidewall height	7.30 in (185.5 mm)	6.50 in (165.1 mm)	−0.80 in (−20.4 mm)	−11.00%
Section width	10.43 in (265.0 mm)	12.50 in (317.5 mm)	+2.07 in (+52.5 mm)	+19.81%
Circumference	102.44 in (2,601.9 mm)	103.67 in (2,633.3 mm)	+1.24 in (+31.4 mm)	+1.21%
Revolutions per mile	619	611	−7	−1.19%

True speed with the speedometer calibrated for 265/70R18
Indicated	Actual on 265/70R18	Actual on 33x12.50R20	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.7 mph	+0.7 mph
75 mph	75.0 mph	75.9 mph	+0.9 mph

Ride-height change: 33x12.50R20 raises the vehicle by 0.20 in (5.0 mm) at the axle (half the +10.0 mm diameter difference).

33x12.50R20 is 0.39 in taller than 265/70R18 and 53 mm wider, a 1.21% difference in overall diameter.

With the speedometer calibrated for 265/70R18, an indicated 60 mph is actually 60.7 mph on 33x12.50R20, and revolutions per mile change from 619 to 611.

33x12.50R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 265/70R18.

Size pages

Other comparisons with 265/70R18

Other comparisons with 33x12.50R20

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