195/60R16 vs 225/40R18

225/40R18 is 0.13 in (3.2 mm) shorter than 195/60R16, a −0.50% diameter difference. With the speedometer set for 195/60R16, an indicated 60 mph is 59.7 mph on 225/40R18.

Is this a safe swap?

Diameter difference −0.50%: under 1%

By overall diameter alone, 225/40R18 is a near match for 195/60R16; 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.

195/60R16 vs 225/40R18 differences
Measurement	195/60R16	225/40R18	Difference	% diff
Overall diameter	25.21 in (640.4 mm)	25.09 in (637.2 mm)	−0.13 in (−3.2 mm)	−0.50%
Sidewall height	4.61 in (117.0 mm)	3.54 in (90.0 mm)	−1.06 in (−27.0 mm)	−23.08%
Section width	7.68 in (195.0 mm)	8.86 in (225.0 mm)	+1.18 in (+30.0 mm)	+15.38%
Circumference	79.21 in (2,011.9 mm)	78.81 in (2,001.8 mm)	−0.40 in (−10.1 mm)	−0.50%
Revolutions per mile	800	804	+4	+0.50%

True speed with the speedometer calibrated for 195/60R16
Indicated	Actual on 195/60R16	Actual on 225/40R18	Difference
30 mph	30.0 mph	29.9 mph	−0.1 mph
60 mph	60.0 mph	59.7 mph	−0.3 mph
75 mph	75.0 mph	74.6 mph	−0.4 mph

Ride-height change: 225/40R18 lowers the vehicle by 0.06 in (1.6 mm) at the axle (half the −3.2 mm diameter difference).

225/40R18 is 0.13 in shorter than 195/60R16 and 30 mm wider, a 0.50% difference in overall diameter.

With the speedometer calibrated for 195/60R16, an indicated 60 mph is actually 59.7 mph on 225/40R18, and revolutions per mile change from 800 to 804.

225/40R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 195/60R16.

Size pages

Other comparisons with 195/60R16

Other comparisons with 225/40R18

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