235/65R16 vs 245/50R18

245/50R18 is 0.38 in (9.7 mm) shorter than 235/65R16, a −1.36% diameter difference. With the speedometer set for 235/65R16, an indicated 60 mph is 59.2 mph on 245/50R18.

Is this a safe swap?

Diameter difference −1.36%: within the ±3% guideline

By overall diameter alone, 245/50R18 falls inside the ±3% range commonly used as a guideline when replacing 235/65R16. 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.

235/65R16 vs 245/50R18 differences
Measurement	235/65R16	245/50R18	Difference	% diff
Overall diameter	28.03 in (711.9 mm)	27.65 in (702.2 mm)	−0.38 in (−9.7 mm)	−1.36%
Sidewall height	6.01 in (152.8 mm)	4.82 in (122.5 mm)	−1.19 in (−30.2 mm)	−19.80%
Section width	9.25 in (235.0 mm)	9.65 in (245.0 mm)	+0.39 in (+10.0 mm)	+4.26%
Circumference	88.05 in (2,236.5 mm)	86.85 in (2,206.0 mm)	−1.20 in (−30.5 mm)	−1.36%
Revolutions per mile	720	730	+10	+1.38%

True speed with the speedometer calibrated for 235/65R16
Indicated	Actual on 235/65R16	Actual on 245/50R18	Difference
30 mph	30.0 mph	29.6 mph	−0.4 mph
60 mph	60.0 mph	59.2 mph	−0.8 mph
75 mph	75.0 mph	74.0 mph	−1.0 mph

Ride-height change: 245/50R18 lowers the vehicle by 0.19 in (4.8 mm) at the axle (half the −9.7 mm diameter difference).

245/50R18 is 0.38 in shorter than 235/65R16 and 10 mm wider, a 1.36% difference in overall diameter.

With the speedometer calibrated for 235/65R16, an indicated 60 mph is actually 59.2 mph on 245/50R18, and revolutions per mile change from 720 to 730.

245/50R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 235/65R16.

Size pages

Other comparisons with 235/65R16

Other comparisons with 245/50R18

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