235/85R16 vs 265/65R18

265/65R18 is 0.17 in (4.2 mm) shorter than 235/85R16, a −0.52% diameter difference. With the speedometer set for 235/85R16, an indicated 60 mph is 59.7 mph on 265/65R18.

Is this a safe swap?

Diameter difference −0.52%: under 1%

By overall diameter alone, 265/65R18 is a near match for 235/85R16; 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.

235/85R16 vs 265/65R18 differences
Measurement	235/85R16	265/65R18	Difference	% diff
Overall diameter	31.73 in (805.9 mm)	31.56 in (801.7 mm)	−0.17 in (−4.2 mm)	−0.52%
Sidewall height	7.86 in (199.8 mm)	6.78 in (172.3 mm)	−1.08 in (−27.5 mm)	−13.77%
Section width	9.25 in (235.0 mm)	10.43 in (265.0 mm)	+1.18 in (+30.0 mm)	+12.77%
Circumference	99.68 in (2,531.8 mm)	99.16 in (2,518.6 mm)	−0.52 in (−13.2 mm)	−0.52%
Revolutions per mile	636	639	+3	+0.52%

True speed with the speedometer calibrated for 235/85R16
Indicated	Actual on 235/85R16	Actual on 265/65R18	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: 265/65R18 lowers the vehicle by 0.08 in (2.1 mm) at the axle (half the −4.2 mm diameter difference).

265/65R18 is 0.17 in shorter than 235/85R16 and 30 mm wider, a 0.52% difference in overall diameter.

With the speedometer calibrated for 235/85R16, an indicated 60 mph is actually 59.7 mph on 265/65R18, and revolutions per mile change from 636 to 639.

265/65R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 235/85R16.

Size pages

Other comparisons with 235/85R16

Other comparisons with 265/65R18

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