215/65R16 vs 235/50R18

235/50R18 is 0.25 in (6.3 mm) taller than 215/65R16, a +0.92% diameter difference. With the speedometer set for 215/65R16, an indicated 60 mph is 60.6 mph on 235/50R18.

Is this a safe swap?

Diameter difference +0.92%: under 1%

By overall diameter alone, 235/50R18 is a near match for 215/65R16; 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.

215/65R16 vs 235/50R18 differences
Measurement	215/65R16	235/50R18	Difference	% diff
Overall diameter	27.00 in (685.9 mm)	27.25 in (692.2 mm)	+0.25 in (+6.3 mm)	+0.92%
Sidewall height	5.50 in (139.8 mm)	4.63 in (117.5 mm)	−0.88 in (−22.2 mm)	−15.92%
Section width	8.46 in (215.0 mm)	9.25 in (235.0 mm)	+0.79 in (+20.0 mm)	+9.30%
Circumference	84.84 in (2,154.8 mm)	85.61 in (2,174.6 mm)	+0.78 in (+19.8 mm)	+0.92%
Revolutions per mile	747	740	−7	−0.91%

True speed with the speedometer calibrated for 215/65R16
Indicated	Actual on 215/65R16	Actual on 235/50R18	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.6 mph	+0.6 mph
75 mph	75.0 mph	75.7 mph	+0.7 mph

Ride-height change: 235/50R18 raises the vehicle by 0.12 in (3.2 mm) at the axle (half the +6.3 mm diameter difference).

235/50R18 is 0.25 in taller than 215/65R16 and 20 mm wider, a 0.92% difference in overall diameter.

With the speedometer calibrated for 215/65R16, an indicated 60 mph is actually 60.6 mph on 235/50R18, and revolutions per mile change from 747 to 740.

235/50R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 215/65R16.

Size pages

Other comparisons with 215/65R16

Other comparisons with 235/50R18

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