265/50R18 vs 245/55R18

245/55R18 is 0.18 in (4.5 mm) taller than 265/50R18, a +0.62% diameter difference. With the speedometer set for 265/50R18, an indicated 60 mph is 60.4 mph on 245/55R18.

Is this a safe swap?

Diameter difference +0.62%: under 1%

By overall diameter alone, 245/55R18 is a near match for 265/50R18; 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.

265/50R18 vs 245/55R18 differences
Measurement	265/50R18	245/55R18	Difference	% diff
Overall diameter	28.43 in (722.2 mm)	28.61 in (726.7 mm)	+0.18 in (+4.5 mm)	+0.62%
Sidewall height	5.22 in (132.5 mm)	5.31 in (134.8 mm)	+0.09 in (+2.3 mm)	+1.70%
Section width	10.43 in (265.0 mm)	9.65 in (245.0 mm)	−0.79 in (−20.0 mm)	−7.55%
Circumference	89.33 in (2,268.9 mm)	89.88 in (2,283.0 mm)	+0.56 in (+14.1 mm)	+0.62%
Revolutions per mile	709	705	−4	−0.62%

True speed with the speedometer calibrated for 265/50R18
Indicated	Actual on 265/50R18	Actual on 245/55R18	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.4 mph	+0.4 mph
75 mph	75.0 mph	75.5 mph	+0.5 mph

Ride-height change: 245/55R18 raises the vehicle by 0.09 in (2.3 mm) at the axle (half the +4.5 mm diameter difference).

245/55R18 is 0.18 in taller than 265/50R18 and 20 mm narrower, a 0.62% difference in overall diameter.

With the speedometer calibrated for 265/50R18, an indicated 60 mph is actually 60.4 mph on 245/55R18, and revolutions per mile change from 709 to 705.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 265/50R18

Other comparisons with 245/55R18

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