205/55R16 vs 255/35R18

255/35R18 is 0.15 in (3.8 mm) taller than 205/55R16, a +0.60% diameter difference. With the speedometer set for 205/55R16, an indicated 60 mph is 60.4 mph on 255/35R18.

Is this a safe swap?

Diameter difference +0.60%: under 1%

By overall diameter alone, 255/35R18 is a near match for 205/55R16; 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.

205/55R16 vs 255/35R18 differences
Measurement	205/55R16	255/35R18	Difference	% diff
Overall diameter	24.88 in (631.9 mm)	25.03 in (635.7 mm)	+0.15 in (+3.8 mm)	+0.60%
Sidewall height	4.44 in (112.8 mm)	3.51 in (89.3 mm)	−0.93 in (−23.5 mm)	−20.84%
Section width	8.07 in (205.0 mm)	10.04 in (255.0 mm)	+1.97 in (+50.0 mm)	+24.39%
Circumference	78.16 in (1,985.2 mm)	78.63 in (1,997.1 mm)	+0.47 in (+11.9 mm)	+0.60%
Revolutions per mile	811	806	−5	−0.60%

True speed with the speedometer calibrated for 205/55R16
Indicated	Actual on 205/55R16	Actual on 255/35R18	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.4 mph	+0.4 mph
75 mph	75.0 mph	75.5 mph	+0.5 mph

Ride-height change: 255/35R18 raises the vehicle by 0.07 in (1.9 mm) at the axle (half the +3.8 mm diameter difference).

255/35R18 is 0.15 in taller than 205/55R16 and 50 mm wider, a 0.60% difference in overall diameter.

With the speedometer calibrated for 205/55R16, an indicated 60 mph is actually 60.4 mph on 255/35R18, and revolutions per mile change from 811 to 806.

255/35R18 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 255/35R18

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