235/75R16 vs 275/55R18

275/55R18 is 0.03 in (0.8 mm) taller than 235/75R16, a +0.11% diameter difference. With the speedometer set for 235/75R16, an indicated 60 mph is 60.1 mph on 275/55R18.

Is this a safe swap?

Diameter difference +0.11%: under 1%

By overall diameter alone, 275/55R18 is a near match for 235/75R16; 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.

235/75R16 vs 275/55R18 differences
Measurement	235/75R16	275/55R18	Difference	% diff
Overall diameter	29.88 in (758.9 mm)	29.91 in (759.7 mm)	+0.03 in (+0.8 mm)	+0.11%
Sidewall height	6.94 in (176.3 mm)	5.95 in (151.3 mm)	−0.98 in (−25.0 mm)	−14.18%
Section width	9.25 in (235.0 mm)	10.83 in (275.0 mm)	+1.57 in (+40.0 mm)	+17.02%
Circumference	93.86 in (2,384.2 mm)	93.96 in (2,386.7 mm)	+0.10 in (+2.5 mm)	+0.11%
Revolutions per mile	675	674	−1	−0.11%

True speed with the speedometer calibrated for 235/75R16
Indicated	Actual on 235/75R16	Actual on 275/55R18	Difference
30 mph	30.0 mph	30.0 mph	0.0 mph
60 mph	60.0 mph	60.1 mph	+0.1 mph
75 mph	75.0 mph	75.1 mph	+0.1 mph

Ride-height change: 275/55R18 raises the vehicle by 0.02 in (0.4 mm) at the axle (half the +0.8 mm diameter difference).

275/55R18 is 0.03 in taller than 235/75R16 and 40 mm wider, a 0.11% difference in overall diameter.

With the speedometer calibrated for 235/75R16, an indicated 60 mph is actually 60.1 mph on 275/55R18, and revolutions per mile change from 675 to 674.

275/55R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 235/75R16.

Size pages

Other comparisons with 235/75R16

Other comparisons with 275/55R18

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