245/70R16 vs 275/55R18

275/55R18 is 0.41 in (10.3 mm) taller than 245/70R16, a +1.37% diameter difference. With the speedometer set for 245/70R16, an indicated 60 mph is 60.8 mph on 275/55R18.

Is this a safe swap?

Diameter difference +1.37%: within the ±3% guideline

By overall diameter alone, 275/55R18 falls inside the ±3% range commonly used as a guideline when replacing 245/70R16. 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.

245/70R16 vs 275/55R18 differences
Measurement	245/70R16	275/55R18	Difference	% diff
Overall diameter	29.50 in (749.4 mm)	29.91 in (759.7 mm)	+0.41 in (+10.3 mm)	+1.37%
Sidewall height	6.75 in (171.5 mm)	5.95 in (151.3 mm)	−0.80 in (−20.2 mm)	−11.81%
Section width	9.65 in (245.0 mm)	10.83 in (275.0 mm)	+1.18 in (+30.0 mm)	+12.24%
Circumference	92.69 in (2,354.3 mm)	93.96 in (2,386.7 mm)	+1.27 in (+32.4 mm)	+1.37%
Revolutions per mile	684	674	−9	−1.36%

True speed with the speedometer calibrated for 245/70R16
Indicated	Actual on 245/70R16	Actual on 275/55R18	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.8 mph	+0.8 mph
75 mph	75.0 mph	76.0 mph	+1.0 mph

Ride-height change: 275/55R18 raises the vehicle by 0.20 in (5.2 mm) at the axle (half the +10.3 mm diameter difference).

275/55R18 is 0.41 in taller than 245/70R16 and 30 mm wider, a 1.37% difference in overall diameter.

With the speedometer calibrated for 245/70R16, an indicated 60 mph is actually 60.8 mph on 275/55R18, and revolutions per mile change from 684 to 674.

275/55R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 245/70R16.

Size pages

Other comparisons with 245/70R16

Other comparisons with 275/55R18

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