255/80R17 vs 275/70R18

275/70R18 is 0.09 in (2.4 mm) taller than 255/80R17, a +0.29% diameter difference. With the speedometer set for 255/80R17, an indicated 60 mph is 60.2 mph on 275/70R18.

Is this a safe swap?

Diameter difference +0.29%: under 1%

By overall diameter alone, 275/70R18 is a near match for 255/80R17; 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.

255/80R17 vs 275/70R18 differences
Measurement	255/80R17	275/70R18	Difference	% diff
Overall diameter	33.06 in (839.8 mm)	33.16 in (842.2 mm)	+0.09 in (+2.4 mm)	+0.29%
Sidewall height	8.03 in (204.0 mm)	7.58 in (192.5 mm)	−0.45 in (−11.5 mm)	−5.64%
Section width	10.04 in (255.0 mm)	10.83 in (275.0 mm)	+0.79 in (+20.0 mm)	+7.84%
Circumference	103.87 in (2,638.3 mm)	104.17 in (2,645.8 mm)	+0.30 in (+7.5 mm)	+0.29%
Revolutions per mile	610	608	−2	−0.28%

True speed with the speedometer calibrated for 255/80R17
Indicated	Actual on 255/80R17	Actual on 275/70R18	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.2 mph	+0.2 mph
75 mph	75.0 mph	75.2 mph	+0.2 mph

Ride-height change: 275/70R18 raises the vehicle by 0.05 in (1.2 mm) at the axle (half the +2.4 mm diameter difference).

275/70R18 is 0.09 in taller than 255/80R17 and 20 mm wider, a 0.29% difference in overall diameter.

With the speedometer calibrated for 255/80R17, an indicated 60 mph is actually 60.2 mph on 275/70R18, and revolutions per mile change from 610 to 608.

275/70R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 255/80R17.

Size pages

Other comparisons with 255/80R17

Other comparisons with 275/70R18

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