205/75R16 vs 235/55R18

235/55R18 is 0.07 in (1.8 mm) taller than 205/75R16, a +0.25% diameter difference. With the speedometer set for 205/75R16, an indicated 60 mph is 60.2 mph on 235/55R18.

Is this a safe swap?

Diameter difference +0.25%: under 1%

By overall diameter alone, 235/55R18 is a near match for 205/75R16; 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.

205/75R16 vs 235/55R18 differences
Measurement	205/75R16	235/55R18	Difference	% diff
Overall diameter	28.11 in (713.9 mm)	28.18 in (715.7 mm)	+0.07 in (+1.8 mm)	+0.25%
Sidewall height	6.05 in (153.8 mm)	5.09 in (129.3 mm)	−0.96 in (−24.5 mm)	−15.93%
Section width	8.07 in (205.0 mm)	9.25 in (235.0 mm)	+1.18 in (+30.0 mm)	+14.63%
Circumference	88.30 in (2,242.8 mm)	88.52 in (2,248.4 mm)	+0.22 in (+5.7 mm)	+0.25%
Revolutions per mile	718	716	−2	−0.25%

True speed with the speedometer calibrated for 205/75R16
Indicated	Actual on 205/75R16	Actual on 235/55R18	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.2 mph	+0.2 mph
75 mph	75.0 mph	75.2 mph	+0.2 mph

Ride-height change: 235/55R18 raises the vehicle by 0.04 in (0.9 mm) at the axle (half the +1.8 mm diameter difference).

235/55R18 is 0.07 in taller than 205/75R16 and 30 mm wider, a 0.25% difference in overall diameter.

With the speedometer calibrated for 205/75R16, an indicated 60 mph is actually 60.2 mph on 235/55R18, and revolutions per mile change from 718 to 716.

235/55R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 205/75R16.

Size pages

Other comparisons with 205/75R16

Other comparisons with 235/55R18

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