275/60R18 vs 255/65R18

255/65R18 is 0.06 in (1.5 mm) taller than 275/60R18, a +0.19% diameter difference. With the speedometer set for 275/60R18, an indicated 60 mph is 60.1 mph on 255/65R18.

Is this a safe swap?

Diameter difference +0.19%: under 1%

By overall diameter alone, 255/65R18 is a near match for 275/60R18; 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.

275/60R18 vs 255/65R18 differences
Measurement	275/60R18	255/65R18	Difference	% diff
Overall diameter	30.99 in (787.2 mm)	31.05 in (788.7 mm)	+0.06 in (+1.5 mm)	+0.19%
Sidewall height	6.50 in (165.0 mm)	6.53 in (165.8 mm)	+0.03 in (+0.8 mm)	+0.45%
Section width	10.83 in (275.0 mm)	10.04 in (255.0 mm)	−0.79 in (−20.0 mm)	−7.27%
Circumference	97.36 in (2,473.1 mm)	97.55 in (2,477.8 mm)	+0.19 in (+4.7 mm)	+0.19%
Revolutions per mile	651	650	−1	−0.19%

True speed with the speedometer calibrated for 275/60R18
Indicated	Actual on 275/60R18	Actual on 255/65R18	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	75.1 mph	+0.1 mph

Ride-height change: 255/65R18 raises the vehicle by 0.03 in (0.8 mm) at the axle (half the +1.5 mm diameter difference).

255/65R18 is 0.06 in taller than 275/60R18 and 20 mm narrower, a 0.19% difference in overall diameter.

With the speedometer calibrated for 275/60R18, an indicated 60 mph is actually 60.1 mph on 255/65R18, and revolutions per mile change from 651 to 650.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 275/60R18

Other comparisons with 255/65R18

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