265/40R18 vs 215/50R18

215/50R18 is 0.12 in (3.0 mm) taller than 265/40R18, a +0.45% diameter difference. With the speedometer set for 265/40R18, an indicated 60 mph is 60.3 mph on 215/50R18.

Is this a safe swap?

Diameter difference +0.45%: under 1%

By overall diameter alone, 215/50R18 is a near match for 265/40R18; 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.

265/40R18 vs 215/50R18 differences
Measurement	265/40R18	215/50R18	Difference	% diff
Overall diameter	26.35 in (669.2 mm)	26.46 in (672.2 mm)	+0.12 in (+3.0 mm)	+0.45%
Sidewall height	4.17 in (106.0 mm)	4.23 in (107.5 mm)	+0.06 in (+1.5 mm)	+1.42%
Section width	10.43 in (265.0 mm)	8.46 in (215.0 mm)	−1.97 in (−50.0 mm)	−18.87%
Circumference	82.77 in (2,102.4 mm)	83.14 in (2,111.8 mm)	+0.37 in (+9.4 mm)	+0.45%
Revolutions per mile	765	762	−3	−0.45%

True speed with the speedometer calibrated for 265/40R18
Indicated	Actual on 265/40R18	Actual on 215/50R18	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.3 mph	+0.3 mph
75 mph	75.0 mph	75.3 mph	+0.3 mph

Ride-height change: 215/50R18 raises the vehicle by 0.06 in (1.5 mm) at the axle (half the +3.0 mm diameter difference).

215/50R18 is 0.12 in taller than 265/40R18 and 50 mm narrower, a 0.45% difference in overall diameter.

With the speedometer calibrated for 265/40R18, an indicated 60 mph is actually 60.3 mph on 215/50R18, and revolutions per mile change from 765 to 762.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 265/40R18

Other comparisons with 215/50R18

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