235/50R18 vs 215/55R18

215/55R18 is 0.06 in (1.5 mm) taller than 235/50R18, a +0.22% diameter difference. With the speedometer set for 235/50R18, an indicated 60 mph is 60.1 mph on 215/55R18.

Is this a safe swap?

Diameter difference +0.22%: under 1%

By overall diameter alone, 215/55R18 is a near match for 235/50R18; 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.

235/50R18 vs 215/55R18 differences
Measurement	235/50R18	215/55R18	Difference	% diff
Overall diameter	27.25 in (692.2 mm)	27.31 in (693.7 mm)	+0.06 in (+1.5 mm)	+0.22%
Sidewall height	4.63 in (117.5 mm)	4.66 in (118.3 mm)	+0.03 in (+0.8 mm)	+0.64%
Section width	9.25 in (235.0 mm)	8.46 in (215.0 mm)	−0.79 in (−20.0 mm)	−8.51%
Circumference	85.61 in (2,174.6 mm)	85.80 in (2,179.3 mm)	+0.19 in (+4.7 mm)	+0.22%
Revolutions per mile	740	738	−2	−0.22%

True speed with the speedometer calibrated for 235/50R18
Indicated	Actual on 235/50R18	Actual on 215/55R18	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.1 mph	+0.1 mph
75 mph	75.0 mph	75.2 mph	+0.2 mph

Ride-height change: 215/55R18 raises the vehicle by 0.03 in (0.8 mm) at the axle (half the +1.5 mm diameter difference).

215/55R18 is 0.06 in taller than 235/50R18 and 20 mm narrower, a 0.22% difference in overall diameter.

With the speedometer calibrated for 235/50R18, an indicated 60 mph is actually 60.1 mph on 215/55R18, and revolutions per mile change from 740 to 738.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 235/50R18

Other comparisons with 215/55R18

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