245/55R17 vs 265/45R18

265/45R18 is 0.22 in (5.6 mm) shorter than 245/55R17, a −0.80% diameter difference. With the speedometer set for 245/55R17, an indicated 60 mph is 59.5 mph on 265/45R18.

Is this a safe swap?

Diameter difference −0.80%: under 1%

By overall diameter alone, 265/45R18 is a near match for 245/55R17; 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.

245/55R17 vs 265/45R18 differences
Measurement	245/55R17	265/45R18	Difference	% diff
Overall diameter	27.61 in (701.3 mm)	27.39 in (695.7 mm)	−0.22 in (−5.6 mm)	−0.80%
Sidewall height	5.31 in (134.8 mm)	4.69 in (119.3 mm)	−0.61 in (−15.5 mm)	−11.50%
Section width	9.65 in (245.0 mm)	10.43 in (265.0 mm)	+0.79 in (+20.0 mm)	+8.16%
Circumference	86.74 in (2,203.2 mm)	86.05 in (2,185.6 mm)	−0.69 in (−17.6 mm)	−0.80%
Revolutions per mile	730	736	+6	+0.80%

True speed with the speedometer calibrated for 245/55R17
Indicated	Actual on 245/55R17	Actual on 265/45R18	Difference
30 mph	30.0 mph	29.8 mph	−0.2 mph
60 mph	60.0 mph	59.5 mph	−0.5 mph
75 mph	75.0 mph	74.4 mph	−0.6 mph

Ride-height change: 265/45R18 lowers the vehicle by 0.11 in (2.8 mm) at the axle (half the −5.6 mm diameter difference).

265/45R18 is 0.22 in shorter than 245/55R17 and 20 mm wider, a 0.80% difference in overall diameter.

With the speedometer calibrated for 245/55R17, an indicated 60 mph is actually 59.5 mph on 265/45R18, and revolutions per mile change from 730 to 736.

265/45R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 245/55R17.

Size pages

Other comparisons with 245/55R17

Other comparisons with 265/45R18

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