205/60R16 vs 245/40R18

245/40R18 is 0.03 in (0.8 mm) taller than 205/60R16, a +0.12% diameter difference. With the speedometer set for 205/60R16, an indicated 60 mph is 60.1 mph on 245/40R18.

Is this a safe swap?

Diameter difference +0.12%: under 1%

By overall diameter alone, 245/40R18 is a near match for 205/60R16; 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.

205/60R16 vs 245/40R18 differences
Measurement	205/60R16	245/40R18	Difference	% diff
Overall diameter	25.69 in (652.4 mm)	25.72 in (653.2 mm)	+0.03 in (+0.8 mm)	+0.12%
Sidewall height	4.84 in (123.0 mm)	3.86 in (98.0 mm)	−0.98 in (−25.0 mm)	−20.33%
Section width	8.07 in (205.0 mm)	9.65 in (245.0 mm)	+1.57 in (+40.0 mm)	+19.51%
Circumference	80.69 in (2,049.6 mm)	80.79 in (2,052.1 mm)	+0.10 in (+2.5 mm)	+0.12%
Revolutions per mile	785	784	−1	−0.12%

True speed with the speedometer calibrated for 205/60R16
Indicated	Actual on 205/60R16	Actual on 245/40R18	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: 245/40R18 raises the vehicle by 0.02 in (0.4 mm) at the axle (half the +0.8 mm diameter difference).

245/40R18 is 0.03 in taller than 205/60R16 and 40 mm wider, a 0.12% difference in overall diameter.

With the speedometer calibrated for 205/60R16, an indicated 60 mph is actually 60.1 mph on 245/40R18, and revolutions per mile change from 785 to 784.

245/40R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 205/60R16.

Size pages

Other comparisons with 205/60R16

Other comparisons with 245/40R18

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