245/45R18 vs 225/50R18

225/50R18 is 0.18 in (4.5 mm) taller than 245/45R18, a +0.66% diameter difference. With the speedometer set for 245/45R18, an indicated 60 mph is 60.4 mph on 225/50R18.

Is this a safe swap?

Diameter difference +0.66%: under 1%

By overall diameter alone, 225/50R18 is a near match for 245/45R18; 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.

245/45R18 vs 225/50R18 differences
Measurement	245/45R18	225/50R18	Difference	% diff
Overall diameter	26.68 in (677.7 mm)	26.86 in (682.2 mm)	+0.18 in (+4.5 mm)	+0.66%
Sidewall height	4.34 in (110.3 mm)	4.43 in (112.5 mm)	+0.09 in (+2.3 mm)	+2.04%
Section width	9.65 in (245.0 mm)	8.86 in (225.0 mm)	−0.79 in (−20.0 mm)	−8.16%
Circumference	83.82 in (2,129.1 mm)	84.38 in (2,143.2 mm)	+0.56 in (+14.1 mm)	+0.66%
Revolutions per mile	756	751	−5	−0.66%

True speed with the speedometer calibrated for 245/45R18
Indicated	Actual on 245/45R18	Actual on 225/50R18	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: 225/50R18 raises the vehicle by 0.09 in (2.3 mm) at the axle (half the +4.5 mm diameter difference).

225/50R18 is 0.18 in taller than 245/45R18 and 20 mm narrower, a 0.66% difference in overall diameter.

With the speedometer calibrated for 245/45R18, an indicated 60 mph is actually 60.4 mph on 225/50R18, and revolutions per mile change from 756 to 751.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 245/45R18

Other comparisons with 225/50R18

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