215/60R17 vs 235/50R18

235/50R18 is 0.09 in (2.4 mm) taller than 215/60R17, a +0.35% diameter difference. With the speedometer set for 215/60R17, an indicated 60 mph is 60.2 mph on 235/50R18.

Is this a safe swap?

Diameter difference +0.35%: under 1%

By overall diameter alone, 235/50R18 is a near match for 215/60R17; 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.

215/60R17 vs 235/50R18 differences
Measurement	215/60R17	235/50R18	Difference	% diff
Overall diameter	27.16 in (689.8 mm)	27.25 in (692.2 mm)	+0.09 in (+2.4 mm)	+0.35%
Sidewall height	5.08 in (129.0 mm)	4.63 in (117.5 mm)	−0.45 in (−11.5 mm)	−8.91%
Section width	8.46 in (215.0 mm)	9.25 in (235.0 mm)	+0.79 in (+20.0 mm)	+9.30%
Circumference	85.32 in (2,167.1 mm)	85.61 in (2,174.6 mm)	+0.30 in (+7.5 mm)	+0.35%
Revolutions per mile	743	740	−3	−0.35%

True speed with the speedometer calibrated for 215/60R17
Indicated	Actual on 215/60R17	Actual on 235/50R18	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.2 mph	+0.2 mph
75 mph	75.0 mph	75.3 mph	+0.3 mph

Ride-height change: 235/50R18 raises the vehicle by 0.05 in (1.2 mm) at the axle (half the +2.4 mm diameter difference).

235/50R18 is 0.09 in taller than 215/60R17 and 20 mm wider, a 0.35% difference in overall diameter.

With the speedometer calibrated for 215/60R17, an indicated 60 mph is actually 60.2 mph on 235/50R18, and revolutions per mile change from 743 to 740.

235/50R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 215/60R17.

Size pages

Other comparisons with 215/60R17

Other comparisons with 235/50R18

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