225/50R18 vs 245/50R18

245/50R18 is 0.79 in (20.0 mm) taller than 225/50R18, a +2.93% diameter difference. With the speedometer set for 225/50R18, an indicated 60 mph is 61.8 mph on 245/50R18.

Is this a safe swap?

Diameter difference +2.93%: within the ±3% guideline

By overall diameter alone, 245/50R18 falls inside the ±3% range commonly used as a guideline when replacing 225/50R18. 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.

225/50R18 vs 245/50R18 differences
Measurement	225/50R18	245/50R18	Difference	% diff
Overall diameter	26.86 in (682.2 mm)	27.65 in (702.2 mm)	+0.79 in (+20.0 mm)	+2.93%
Sidewall height	4.43 in (112.5 mm)	4.82 in (122.5 mm)	+0.39 in (+10.0 mm)	+8.89%
Section width	8.86 in (225.0 mm)	9.65 in (245.0 mm)	+0.79 in (+20.0 mm)	+8.89%
Circumference	84.38 in (2,143.2 mm)	86.85 in (2,206.0 mm)	+2.47 in (+62.8 mm)	+2.93%
Revolutions per mile	751	730	−21	−2.85%

True speed with the speedometer calibrated for 225/50R18
Indicated	Actual on 225/50R18	Actual on 245/50R18	Difference
30 mph	30.0 mph	30.9 mph	+0.9 mph
60 mph	60.0 mph	61.8 mph	+1.8 mph
75 mph	75.0 mph	77.2 mph	+2.2 mph

Ride-height change: 245/50R18 raises the vehicle by 0.39 in (10.0 mm) at the axle (half the +20.0 mm diameter difference).

245/50R18 is 0.79 in taller than 225/50R18 and 20 mm wider, a 2.93% difference in overall diameter.

With the speedometer calibrated for 225/50R18, an indicated 60 mph is actually 61.8 mph on 245/50R18, and revolutions per mile change from 751 to 730.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 225/50R18

Other comparisons with 245/50R18

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