225/65R16 vs 235/50R18

235/50R18 is 0.26 in (6.7 mm) shorter than 225/65R16, a −0.96% diameter difference. With the speedometer set for 225/65R16, an indicated 60 mph is 59.4 mph on 235/50R18.

Is this a safe swap?

Diameter difference −0.96%: under 1%

By overall diameter alone, 235/50R18 is a near match for 225/65R16; 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.

225/65R16 vs 235/50R18 differences
Measurement	225/65R16	235/50R18	Difference	% diff
Overall diameter	27.52 in (698.9 mm)	27.25 in (692.2 mm)	−0.26 in (−6.7 mm)	−0.96%
Sidewall height	5.76 in (146.3 mm)	4.63 in (117.5 mm)	−1.13 in (−28.7 mm)	−19.66%
Section width	8.86 in (225.0 mm)	9.25 in (235.0 mm)	+0.39 in (+10.0 mm)	+4.44%
Circumference	86.44 in (2,195.7 mm)	85.61 in (2,174.6 mm)	−0.83 in (−21.0 mm)	−0.96%
Revolutions per mile	733	740	+7	+0.97%

True speed with the speedometer calibrated for 225/65R16
Indicated	Actual on 225/65R16	Actual on 235/50R18	Difference
30 mph	30.0 mph	29.7 mph	−0.3 mph
60 mph	60.0 mph	59.4 mph	−0.6 mph
75 mph	75.0 mph	74.3 mph	−0.7 mph

Ride-height change: 235/50R18 lowers the vehicle by 0.13 in (3.3 mm) at the axle (half the −6.7 mm diameter difference).

235/50R18 is 0.26 in shorter than 225/65R16 and 10 mm wider, a 0.96% difference in overall diameter.

With the speedometer calibrated for 225/65R16, an indicated 60 mph is actually 59.4 mph on 235/50R18, and revolutions per mile change from 733 to 740.

235/50R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 225/65R16.

Size pages

Other comparisons with 225/65R16

Other comparisons with 235/50R18

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