225/65R17 vs 245/55R18

245/55R18 is 0.09 in (2.4 mm) taller than 225/65R17, a +0.33% diameter difference. With the speedometer set for 225/65R17, an indicated 60 mph is 60.2 mph on 245/55R18.

Is this a safe swap?

Diameter difference +0.33%: under 1%

By overall diameter alone, 245/55R18 is a near match for 225/65R17; 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.

225/65R17 vs 245/55R18 differences
Measurement	225/65R17	245/55R18	Difference	% diff
Overall diameter	28.52 in (724.3 mm)	28.61 in (726.7 mm)	+0.09 in (+2.4 mm)	+0.33%
Sidewall height	5.76 in (146.3 mm)	5.31 in (134.8 mm)	−0.45 in (−11.5 mm)	−7.86%
Section width	8.86 in (225.0 mm)	9.65 in (245.0 mm)	+0.79 in (+20.0 mm)	+8.89%
Circumference	89.58 in (2,275.5 mm)	89.88 in (2,283.0 mm)	+0.30 in (+7.5 mm)	+0.33%
Revolutions per mile	707	705	−2	−0.33%

True speed with the speedometer calibrated for 225/65R17
Indicated	Actual on 225/65R17	Actual on 245/55R18	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: 245/55R18 raises the vehicle by 0.05 in (1.2 mm) at the axle (half the +2.4 mm diameter difference).

245/55R18 is 0.09 in taller than 225/65R17 and 20 mm wider, a 0.33% difference in overall diameter.

With the speedometer calibrated for 225/65R17, an indicated 60 mph is actually 60.2 mph on 245/55R18, and revolutions per mile change from 707 to 705.

245/55R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 225/65R17.

Size pages

Other comparisons with 225/65R17

Other comparisons with 245/55R18

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