255/70R18 vs 275/65R18

275/65R18 is 0.02 in (0.5 mm) taller than 255/70R18, a +0.06% diameter difference. With the speedometer set for 255/70R18, an indicated 60 mph is 60.0 mph on 275/65R18.

Is this a safe swap?

Diameter difference +0.06%: under 1%

By overall diameter alone, 275/65R18 is a near match for 255/70R18; 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.

255/70R18 vs 275/65R18 differences
Measurement	255/70R18	275/65R18	Difference	% diff
Overall diameter	32.06 in (814.2 mm)	32.07 in (814.7 mm)	+0.02 in (+0.5 mm)	+0.06%
Sidewall height	7.03 in (178.5 mm)	7.04 in (178.8 mm)	+0.01 in (+0.3 mm)	+0.14%
Section width	10.04 in (255.0 mm)	10.83 in (275.0 mm)	+0.79 in (+20.0 mm)	+7.84%
Circumference	100.70 in (2,557.9 mm)	100.77 in (2,559.5 mm)	+0.06 in (+1.6 mm)	+0.06%
Revolutions per mile	629	629	0	−0.06%

True speed with the speedometer calibrated for 255/70R18
Indicated	Actual on 255/70R18	Actual on 275/65R18
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: 275/65R18 raises the vehicle by 0.01 in (0.3 mm) at the axle (half the +0.5 mm diameter difference).

275/65R18 is 0.02 in taller than 255/70R18 and 20 mm wider, a 0.06% difference in overall diameter.

With the speedometer calibrated for 255/70R18, an indicated 60 mph is actually 60.0 mph on 275/65R18, and revolutions per mile change from 629 to 629.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 255/70R18

Other comparisons with 275/65R18

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