225/50R16 vs 235/35R18

235/35R18 is 0.38 in (9.7 mm) shorter than 225/50R16, a −1.54% diameter difference. With the speedometer set for 225/50R16, an indicated 60 mph is 59.1 mph on 235/35R18.

Is this a safe swap?

Diameter difference −1.54%: within the ±3% guideline

By overall diameter alone, 235/35R18 falls inside the ±3% range commonly used as a guideline when replacing 225/50R16. 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.

225/50R16 vs 235/35R18 differences
Measurement	225/50R16	235/35R18	Difference	% diff
Overall diameter	24.86 in (631.4 mm)	24.48 in (621.7 mm)	−0.38 in (−9.7 mm)	−1.54%
Sidewall height	4.43 in (112.5 mm)	3.24 in (82.3 mm)	−1.19 in (−30.2 mm)	−26.89%
Section width	8.86 in (225.0 mm)	9.25 in (235.0 mm)	+0.39 in (+10.0 mm)	+4.44%
Circumference	78.09 in (1,983.6 mm)	76.89 in (1,953.1 mm)	−1.20 in (−30.5 mm)	−1.54%
Revolutions per mile	811	824	+13	+1.56%

True speed with the speedometer calibrated for 225/50R16
Indicated	Actual on 225/50R16	Actual on 235/35R18	Difference
30 mph	30.0 mph	29.5 mph	−0.5 mph
60 mph	60.0 mph	59.1 mph	−0.9 mph
75 mph	75.0 mph	73.8 mph	−1.2 mph

Ride-height change: 235/35R18 lowers the vehicle by 0.19 in (4.8 mm) at the axle (half the −9.7 mm diameter difference).

235/35R18 is 0.38 in shorter than 225/50R16 and 10 mm wider, a 1.54% difference in overall diameter.

With the speedometer calibrated for 225/50R16, an indicated 60 mph is actually 59.1 mph on 235/35R18, and revolutions per mile change from 811 to 824.

235/35R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 225/50R16.

Size pages

Other comparisons with 225/50R16

Other comparisons with 235/35R18

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