205/55R16 vs 235/35R18

235/35R18 is 0.40 in (10.2 mm) shorter than 205/55R16, a −1.61% diameter difference. With the speedometer set for 205/55R16, an indicated 60 mph is 59.0 mph on 235/35R18.

Is this a safe swap?

Diameter difference −1.61%: within the ±3% guideline

By overall diameter alone, 235/35R18 falls inside the ±3% range commonly used as a guideline when replacing 205/55R16. 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.

205/55R16 vs 235/35R18 differences
Measurement	205/55R16	235/35R18	Difference	% diff
Overall diameter	24.88 in (631.9 mm)	24.48 in (621.7 mm)	−0.40 in (−10.2 mm)	−1.61%
Sidewall height	4.44 in (112.8 mm)	3.24 in (82.3 mm)	−1.20 in (−30.5 mm)	−27.05%
Section width	8.07 in (205.0 mm)	9.25 in (235.0 mm)	+1.18 in (+30.0 mm)	+14.63%
Circumference	78.16 in (1,985.2 mm)	76.89 in (1,953.1 mm)	−1.26 in (−32.0 mm)	−1.61%
Revolutions per mile	811	824	+13	+1.64%

True speed with the speedometer calibrated for 205/55R16
Indicated	Actual on 205/55R16	Actual on 235/35R18	Difference
30 mph	30.0 mph	29.5 mph	−0.5 mph
60 mph	60.0 mph	59.0 mph	−1.0 mph
75 mph	75.0 mph	73.8 mph	−1.2 mph

Ride-height change: 235/35R18 lowers the vehicle by 0.20 in (5.1 mm) at the axle (half the −10.2 mm diameter difference).

235/35R18 is 0.40 in shorter than 205/55R16 and 30 mm wider, a 1.61% difference in overall diameter.

With the speedometer calibrated for 205/55R16, an indicated 60 mph is actually 59.0 mph on 235/35R18, and revolutions per mile change from 811 to 824.

235/35R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 205/55R16.

Size pages

Other comparisons with 205/55R16

Other comparisons with 235/35R18

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