215/50R18 vs 275/40R18

275/40R18 is 0.20 in (5.0 mm) taller than 215/50R18, a +0.74% diameter difference. With the speedometer set for 215/50R18, an indicated 60 mph is 60.4 mph on 275/40R18.

Is this a safe swap?

Diameter difference +0.74%: under 1%

By overall diameter alone, 275/40R18 is a near match for 215/50R18; 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.

215/50R18 vs 275/40R18 differences
Measurement	215/50R18	275/40R18	Difference	% diff
Overall diameter	26.46 in (672.2 mm)	26.66 in (677.2 mm)	+0.20 in (+5.0 mm)	+0.74%
Sidewall height	4.23 in (107.5 mm)	4.33 in (110.0 mm)	+0.10 in (+2.5 mm)	+2.33%
Section width	8.46 in (215.0 mm)	10.83 in (275.0 mm)	+2.36 in (+60.0 mm)	+27.91%
Circumference	83.14 in (2,111.8 mm)	83.76 in (2,127.5 mm)	+0.62 in (+15.7 mm)	+0.74%
Revolutions per mile	762	756	−6	−0.74%

True speed with the speedometer calibrated for 215/50R18
Indicated	Actual on 215/50R18	Actual on 275/40R18	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.4 mph	+0.4 mph
75 mph	75.0 mph	75.6 mph	+0.6 mph

Ride-height change: 275/40R18 raises the vehicle by 0.10 in (2.5 mm) at the axle (half the +5.0 mm diameter difference).

275/40R18 is 0.20 in taller than 215/50R18 and 60 mm wider, a 0.74% difference in overall diameter.

With the speedometer calibrated for 215/50R18, an indicated 60 mph is actually 60.4 mph on 275/40R18, and revolutions per mile change from 762 to 756.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 215/50R18

Other comparisons with 275/40R18

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