195/60R16 vs 235/40R18

235/40R18 is 0.19 in (4.8 mm) taller than 195/60R16, a +0.75% diameter difference. With the speedometer set for 195/60R16, an indicated 60 mph is 60.4 mph on 235/40R18.

Is this a safe swap?

Diameter difference +0.75%: under 1%

By overall diameter alone, 235/40R18 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 235/40R18 differences
Measurement	195/60R16	235/40R18	Difference	% diff
Overall diameter	25.21 in (640.4 mm)	25.40 in (645.2 mm)	+0.19 in (+4.8 mm)	+0.75%
Sidewall height	4.61 in (117.0 mm)	3.70 in (94.0 mm)	−0.91 in (−23.0 mm)	−19.66%
Section width	7.68 in (195.0 mm)	9.25 in (235.0 mm)	+1.57 in (+40.0 mm)	+20.51%
Circumference	79.21 in (2,011.9 mm)	79.80 in (2,027.0 mm)	+0.59 in (+15.1 mm)	+0.75%
Revolutions per mile	800	794	−6	−0.74%

True speed with the speedometer calibrated for 195/60R16
Indicated	Actual on 195/60R16	Actual on 235/40R18	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: 235/40R18 raises the vehicle by 0.09 in (2.4 mm) at the axle (half the +4.8 mm diameter difference).

235/40R18 is 0.19 in taller than 195/60R16 and 40 mm wider, a 0.75% difference in overall diameter.

With the speedometer calibrated for 195/60R16, an indicated 60 mph is actually 60.4 mph on 235/40R18, and revolutions per mile change from 800 to 794.

235/40R18 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 235/40R18

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