185/60R16 vs 255/35R18

255/35R18 is 0.29 in (7.3 mm) taller than 185/60R16, a +1.16% diameter difference. With the speedometer set for 185/60R16, an indicated 60 mph is 60.7 mph on 255/35R18.

Is this a safe swap?

Diameter difference +1.16%: within the ±3% guideline

By overall diameter alone, 255/35R18 falls inside the ±3% range commonly used as a guideline when replacing 185/60R16. 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.

185/60R16 vs 255/35R18 differences
Measurement	185/60R16	255/35R18	Difference	% diff
Overall diameter	24.74 in (628.4 mm)	25.03 in (635.7 mm)	+0.29 in (+7.3 mm)	+1.16%
Sidewall height	4.37 in (111.0 mm)	3.51 in (89.3 mm)	−0.86 in (−21.7 mm)	−19.59%
Section width	7.28 in (185.0 mm)	10.04 in (255.0 mm)	+2.76 in (+70.0 mm)	+37.84%
Circumference	77.72 in (1,974.2 mm)	78.63 in (1,997.1 mm)	+0.90 in (+22.9 mm)	+1.16%
Revolutions per mile	815	806	−9	−1.15%

True speed with the speedometer calibrated for 185/60R16
Indicated	Actual on 185/60R16	Actual on 255/35R18	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.7 mph	+0.7 mph
75 mph	75.0 mph	75.9 mph	+0.9 mph

Ride-height change: 255/35R18 raises the vehicle by 0.14 in (3.7 mm) at the axle (half the +7.3 mm diameter difference).

255/35R18 is 0.29 in taller than 185/60R16 and 70 mm wider, a 1.16% difference in overall diameter.

With the speedometer calibrated for 185/60R16, an indicated 60 mph is actually 60.7 mph on 255/35R18, and revolutions per mile change from 815 to 806.

255/35R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 185/60R16.

Size pages

Other comparisons with 185/60R16

Other comparisons with 255/35R18

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