255/55R18 vs 235/60R18

235/60R18 is 0.06 in (1.5 mm) taller than 255/55R18, a +0.20% diameter difference. With the speedometer set for 255/55R18, an indicated 60 mph is 60.1 mph on 235/60R18.

Is this a safe swap?

Diameter difference +0.20%: under 1%

By overall diameter alone, 235/60R18 is a near match for 255/55R18; 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.

255/55R18 vs 235/60R18 differences
Measurement	255/55R18	235/60R18	Difference	% diff
Overall diameter	29.04 in (737.7 mm)	29.10 in (739.2 mm)	+0.06 in (+1.5 mm)	+0.20%
Sidewall height	5.52 in (140.3 mm)	5.55 in (141.0 mm)	+0.03 in (+0.8 mm)	+0.53%
Section width	10.04 in (255.0 mm)	9.25 in (235.0 mm)	−0.79 in (−20.0 mm)	−7.84%
Circumference	91.24 in (2,317.6 mm)	91.43 in (2,322.3 mm)	+0.19 in (+4.7 mm)	+0.20%
Revolutions per mile	694	693	−1	−0.20%

True speed with the speedometer calibrated for 255/55R18
Indicated	Actual on 255/55R18	Actual on 235/60R18	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.1 mph	+0.1 mph
75 mph	75.0 mph	75.2 mph	+0.2 mph

Ride-height change: 235/60R18 raises the vehicle by 0.03 in (0.8 mm) at the axle (half the +1.5 mm diameter difference).

235/60R18 is 0.06 in taller than 255/55R18 and 20 mm narrower, a 0.20% difference in overall diameter.

With the speedometer calibrated for 255/55R18, an indicated 60 mph is actually 60.1 mph on 235/60R18, and revolutions per mile change from 694 to 693.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 255/55R18

Other comparisons with 235/60R18

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