33x12.50R18 vs 275/70R18

275/70R18 is 0.16 in (4.0 mm) taller than 33x12.50R18, a +0.48% diameter difference. With the speedometer set for 33x12.50R18, an indicated 60 mph is 60.3 mph on 275/70R18.

Is this a safe swap?

Diameter difference +0.48%: under 1%

By overall diameter alone, 275/70R18 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 275/70R18 differences
Measurement	33x12.50R18	275/70R18	Difference	% diff
Overall diameter	33.00 in (838.2 mm)	33.16 in (842.2 mm)	+0.16 in (+4.0 mm)	+0.48%
Sidewall height	7.50 in (190.5 mm)	7.58 in (192.5 mm)	+0.08 in (+2.0 mm)	+1.05%
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)	104.17 in (2,645.8 mm)	+0.49 in (+12.6 mm)	+0.48%
Revolutions per mile	611	608	−3	−0.47%

True speed with the speedometer calibrated for 33x12.50R18
Indicated	Actual on 33x12.50R18	Actual on 275/70R18	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.3 mph	+0.3 mph
75 mph	75.0 mph	75.4 mph	+0.4 mph

Ride-height change: 275/70R18 raises the vehicle by 0.08 in (2.0 mm) at the axle (half the +4.0 mm diameter difference).

275/70R18 is 0.16 in taller than 33x12.50R18 and 43 mm narrower, a 0.48% difference in overall diameter.

With the speedometer calibrated for 33x12.50R18, an indicated 60 mph is actually 60.3 mph on 275/70R18, and revolutions per mile change from 611 to 608.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 33x12.50R18

Other comparisons with 275/70R18

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