235/50R18 vs 245/50R18

245/50R18 is 0.39 in (10.0 mm) taller than 235/50R18, a +1.44% diameter difference. With the speedometer set for 235/50R18, an indicated 60 mph is 60.9 mph on 245/50R18.

Is this a safe swap?

Diameter difference +1.44%: within the ±3% guideline

By overall diameter alone, 245/50R18 falls inside the ±3% range commonly used as a guideline when replacing 235/50R18. 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.

235/50R18 vs 245/50R18 differences
Measurement	235/50R18	245/50R18	Difference	% diff
Overall diameter	27.25 in (692.2 mm)	27.65 in (702.2 mm)	+0.39 in (+10.0 mm)	+1.44%
Sidewall height	4.63 in (117.5 mm)	4.82 in (122.5 mm)	+0.20 in (+5.0 mm)	+4.26%
Section width	9.25 in (235.0 mm)	9.65 in (245.0 mm)	+0.39 in (+10.0 mm)	+4.26%
Circumference	85.61 in (2,174.6 mm)	86.85 in (2,206.0 mm)	+1.24 in (+31.4 mm)	+1.44%
Revolutions per mile	740	730	−11	−1.42%

True speed with the speedometer calibrated for 235/50R18
Indicated	Actual on 235/50R18	Actual on 245/50R18	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.9 mph	+0.9 mph
75 mph	75.0 mph	76.1 mph	+1.1 mph

Ride-height change: 245/50R18 raises the vehicle by 0.20 in (5.0 mm) at the axle (half the +10.0 mm diameter difference).

245/50R18 is 0.39 in taller than 235/50R18 and 10 mm wider, a 1.44% difference in overall diameter.

With the speedometer calibrated for 235/50R18, an indicated 60 mph is actually 60.9 mph on 245/50R18, and revolutions per mile change from 740 to 730.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 235/50R18

Other comparisons with 245/50R18

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