265/65R18 vs 33x12.50R18

33x12.50R18 is 1.44 in (36.5 mm) taller than 265/65R18, a +4.55% diameter difference. With the speedometer set for 265/65R18, an indicated 60 mph is 62.7 mph on 33x12.50R18.

Is this a safe swap?

Diameter difference +4.55%: outside the ±3% guideline

By overall diameter alone, 33x12.50R18 falls outside the ±3% range commonly used as a guideline when replacing 265/65R18; 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.

265/65R18 vs 33x12.50R18 differences
Measurement	265/65R18	33x12.50R18	Difference	% diff
Overall diameter	31.56 in (801.7 mm)	33.00 in (838.2 mm)	+1.44 in (+36.5 mm)	+4.55%
Sidewall height	6.78 in (172.3 mm)	7.50 in (190.5 mm)	+0.72 in (+18.3 mm)	+10.60%
Section width	10.43 in (265.0 mm)	12.50 in (317.5 mm)	+2.07 in (+52.5 mm)	+19.81%
Circumference	99.16 in (2,518.6 mm)	103.67 in (2,633.3 mm)	+4.51 in (+114.7 mm)	+4.55%
Revolutions per mile	639	611	−28	−4.35%

True speed with the speedometer calibrated for 265/65R18
Indicated	Actual on 265/65R18	Actual on 33x12.50R18	Difference
30 mph	30.0 mph	31.4 mph	+1.4 mph
60 mph	60.0 mph	62.7 mph	+2.7 mph
75 mph	75.0 mph	78.4 mph	+3.4 mph

Ride-height change: 33x12.50R18 raises the vehicle by 0.72 in (18.3 mm) at the axle (half the +36.5 mm diameter difference).

33x12.50R18 is 1.44 in taller than 265/65R18 and 53 mm wider, a 4.55% difference in overall diameter.

With the speedometer calibrated for 265/65R18, an indicated 60 mph is actually 62.7 mph on 33x12.50R18, and revolutions per mile change from 639 to 611.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 265/65R18

Other comparisons with 33x12.50R18

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