245/60R18 vs 275/55R18

275/55R18 is 0.33 in (8.5 mm) taller than 245/60R18, a +1.13% diameter difference. With the speedometer set for 245/60R18, an indicated 60 mph is 60.7 mph on 275/55R18.

Is this a safe swap?

Diameter difference +1.13%: within the ±3% guideline

By overall diameter alone, 275/55R18 falls inside the ±3% range commonly used as a guideline when replacing 245/60R18. 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.

245/60R18 vs 275/55R18 differences
Measurement	245/60R18	275/55R18	Difference	% diff
Overall diameter	29.57 in (751.2 mm)	29.91 in (759.7 mm)	+0.33 in (+8.5 mm)	+1.13%
Sidewall height	5.79 in (147.0 mm)	5.95 in (151.3 mm)	+0.17 in (+4.3 mm)	+2.89%
Section width	9.65 in (245.0 mm)	10.83 in (275.0 mm)	+1.18 in (+30.0 mm)	+12.24%
Circumference	92.91 in (2,360.0 mm)	93.96 in (2,386.7 mm)	+1.05 in (+26.7 mm)	+1.13%
Revolutions per mile	682	674	−8	−1.12%

True speed with the speedometer calibrated for 245/60R18
Indicated	Actual on 245/60R18	Actual on 275/55R18	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.7 mph	+0.7 mph
75 mph	75.0 mph	75.8 mph	+0.8 mph

Ride-height change: 275/55R18 raises the vehicle by 0.17 in (4.3 mm) at the axle (half the +8.5 mm diameter difference).

275/55R18 is 0.33 in taller than 245/60R18 and 30 mm wider, a 1.13% difference in overall diameter.

With the speedometer calibrated for 245/60R18, an indicated 60 mph is actually 60.7 mph on 275/55R18, and revolutions per mile change from 682 to 674.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 245/60R18

Other comparisons with 275/55R18

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