245/50R18 vs 225/55R18

225/55R18 is 0.10 in (2.5 mm) taller than 245/50R18, a +0.36% diameter difference. With the speedometer set for 245/50R18, an indicated 60 mph is 60.2 mph on 225/55R18.

Is this a safe swap?

Diameter difference +0.36%: under 1%

By overall diameter alone, 225/55R18 is a near match for 245/50R18; 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.

245/50R18 vs 225/55R18 differences
Measurement	245/50R18	225/55R18	Difference	% diff
Overall diameter	27.65 in (702.2 mm)	27.74 in (704.7 mm)	+0.10 in (+2.5 mm)	+0.36%
Sidewall height	4.82 in (122.5 mm)	4.87 in (123.8 mm)	+0.05 in (+1.3 mm)	+1.02%
Section width	9.65 in (245.0 mm)	8.86 in (225.0 mm)	−0.79 in (−20.0 mm)	−8.16%
Circumference	86.85 in (2,206.0 mm)	87.16 in (2,213.9 mm)	+0.31 in (+7.9 mm)	+0.36%
Revolutions per mile	730	727	−3	−0.35%

True speed with the speedometer calibrated for 245/50R18
Indicated	Actual on 245/50R18	Actual on 225/55R18	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	75.3 mph	+0.3 mph

Ride-height change: 225/55R18 raises the vehicle by 0.05 in (1.3 mm) at the axle (half the +2.5 mm diameter difference).

225/55R18 is 0.10 in taller than 245/50R18 and 20 mm narrower, a 0.36% difference in overall diameter.

With the speedometer calibrated for 245/50R18, an indicated 60 mph is actually 60.2 mph on 225/55R18, and revolutions per mile change from 730 to 727.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 245/50R18

Other comparisons with 225/55R18

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