235/65R18 vs 255/60R18

255/60R18 is 0.02 in (0.5 mm) taller than 235/65R18, a +0.07% diameter difference. With the speedometer set for 235/65R18, an indicated 60 mph is 60.0 mph on 255/60R18.

Is this a safe swap?

Diameter difference +0.07%: under 1%

By overall diameter alone, 255/60R18 is a near match for 235/65R18; 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.

235/65R18 vs 255/60R18 differences
Measurement	235/65R18	255/60R18	Difference	% diff
Overall diameter	30.03 in (762.7 mm)	30.05 in (763.2 mm)	+0.02 in (+0.5 mm)	+0.07%
Sidewall height	6.01 in (152.8 mm)	6.02 in (153.0 mm)	+0.01 in (+0.3 mm)	+0.16%
Section width	9.25 in (235.0 mm)	10.04 in (255.0 mm)	+0.79 in (+20.0 mm)	+8.51%
Circumference	94.33 in (2,396.1 mm)	94.40 in (2,397.7 mm)	+0.06 in (+1.6 mm)	+0.07%
Revolutions per mile	672	671	0	−0.07%

True speed with the speedometer calibrated for 235/65R18
Indicated	Actual on 235/65R18	Actual on 255/60R18
30 mph	30.0 mph	30.0 mph
60 mph	60.0 mph	60.0 mph
75 mph	75.0 mph	75.0 mph

Ride-height change: 255/60R18 raises the vehicle by 0.01 in (0.3 mm) at the axle (half the +0.5 mm diameter difference).

255/60R18 is 0.02 in taller than 235/65R18 and 20 mm wider, a 0.07% difference in overall diameter.

With the speedometer calibrated for 235/65R18, an indicated 60 mph is actually 60.0 mph on 255/60R18, and revolutions per mile change from 672 to 671.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 235/65R18

Other comparisons with 255/60R18

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