205/65R16 vs 265/40R18

265/40R18 is 0.15 in (3.7 mm) shorter than 205/65R16, a −0.55% diameter difference. With the speedometer set for 205/65R16, an indicated 60 mph is 59.7 mph on 265/40R18.

Is this a safe swap?

Diameter difference −0.55%: under 1%

By overall diameter alone, 265/40R18 is a near match for 205/65R16; 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.

205/65R16 vs 265/40R18 differences
Measurement	205/65R16	265/40R18	Difference	% diff
Overall diameter	26.49 in (672.9 mm)	26.35 in (669.2 mm)	−0.15 in (−3.7 mm)	−0.55%
Sidewall height	5.25 in (133.3 mm)	4.17 in (106.0 mm)	−1.07 in (−27.2 mm)	−20.45%
Section width	8.07 in (205.0 mm)	10.43 in (265.0 mm)	+2.36 in (+60.0 mm)	+29.27%
Circumference	83.23 in (2,114.0 mm)	82.77 in (2,102.4 mm)	−0.46 in (−11.6 mm)	−0.55%
Revolutions per mile	761	765	+4	+0.55%

True speed with the speedometer calibrated for 205/65R16
Indicated	Actual on 205/65R16	Actual on 265/40R18	Difference
30 mph	30.0 mph	29.8 mph	−0.2 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: 265/40R18 lowers the vehicle by 0.07 in (1.8 mm) at the axle (half the −3.7 mm diameter difference).

265/40R18 is 0.15 in shorter than 205/65R16 and 60 mm wider, a 0.55% difference in overall diameter.

With the speedometer calibrated for 205/65R16, an indicated 60 mph is actually 59.7 mph on 265/40R18, and revolutions per mile change from 761 to 765.

265/40R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 205/65R16.

Size pages

Other comparisons with 205/65R16

Other comparisons with 265/40R18

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