225/60R16 vs 275/40R18

275/40R18 is 0.03 in (0.8 mm) taller than 225/60R16, a +0.12% diameter difference. With the speedometer set for 225/60R16, an indicated 60 mph is 60.1 mph on 275/40R18.

Is this a safe swap?

Diameter difference +0.12%: under 1%

By overall diameter alone, 275/40R18 is a near match for 225/60R16; 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.

225/60R16 vs 275/40R18 differences
Measurement	225/60R16	275/40R18	Difference	% diff
Overall diameter	26.63 in (676.4 mm)	26.66 in (677.2 mm)	+0.03 in (+0.8 mm)	+0.12%
Sidewall height	5.31 in (135.0 mm)	4.33 in (110.0 mm)	−0.98 in (−25.0 mm)	−18.52%
Section width	8.86 in (225.0 mm)	10.83 in (275.0 mm)	+1.97 in (+50.0 mm)	+22.22%
Circumference	83.66 in (2,125.0 mm)	83.76 in (2,127.5 mm)	+0.10 in (+2.5 mm)	+0.12%
Revolutions per mile	757	756	−1	−0.12%

True speed with the speedometer calibrated for 225/60R16
Indicated	Actual on 225/60R16	Actual on 275/40R18	Difference
30 mph	30.0 mph	30.0 mph	0.0 mph
60 mph	60.0 mph	60.1 mph	+0.1 mph
75 mph	75.0 mph	75.1 mph	+0.1 mph

Ride-height change: 275/40R18 raises the vehicle by 0.02 in (0.4 mm) at the axle (half the +0.8 mm diameter difference).

275/40R18 is 0.03 in taller than 225/60R16 and 50 mm wider, a 0.12% difference in overall diameter.

With the speedometer calibrated for 225/60R16, an indicated 60 mph is actually 60.1 mph on 275/40R18, and revolutions per mile change from 757 to 756.

275/40R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 225/60R16.

Size pages

Other comparisons with 225/60R16

Other comparisons with 275/40R18

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