245/60R17 vs 245/55R18

245/55R18 is 0.04 in (0.9 mm) taller than 245/60R17, a +0.12% diameter difference. With the speedometer set for 245/60R17, an indicated 60 mph is 60.1 mph on 245/55R18.

Is this a safe swap?

Diameter difference +0.12%: under 1%

By overall diameter alone, 245/55R18 is a near match for 245/60R17; 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.

245/60R17 vs 245/55R18 differences
Measurement	245/60R17	245/55R18	Difference	% diff
Overall diameter	28.57 in (725.8 mm)	28.61 in (726.7 mm)	+0.04 in (+0.9 mm)	+0.12%
Sidewall height	5.79 in (147.0 mm)	5.31 in (134.8 mm)	−0.48 in (−12.2 mm)	−8.33%
Section width	9.65 in (245.0 mm)	9.65 in (245.0 mm)	0.00 in (0.0 mm)	0.00%
Circumference	89.77 in (2,280.2 mm)	89.88 in (2,283.0 mm)	+0.11 in (+2.8 mm)	+0.12%
Revolutions per mile	706	705	−1	−0.12%

True speed with the speedometer calibrated for 245/60R17
Indicated	Actual on 245/60R17	Actual on 245/55R18	Difference
30 mph	30.0 mph	30.0 mph	0.0 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: 245/55R18 raises the vehicle by 0.02 in (0.5 mm) at the axle (half the +0.9 mm diameter difference).

245/55R18 is 0.04 in taller than 245/60R17 and the same width, a 0.12% difference in overall diameter.

With the speedometer calibrated for 245/60R17, an indicated 60 mph is actually 60.1 mph on 245/55R18, and revolutions per mile change from 706 to 705.

245/55R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 245/60R17.

Size pages

Other comparisons with 245/60R17

Other comparisons with 245/55R18

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