245/75R16 vs 235/65R18

235/65R18 is 0.44 in (11.2 mm) shorter than 245/75R16, a −1.45% diameter difference. With the speedometer set for 245/75R16, an indicated 60 mph is 59.1 mph on 235/65R18.

Is this a safe swap?

Diameter difference −1.45%: within the ±3% guideline

By overall diameter alone, 235/65R18 falls inside the ±3% range commonly used as a guideline when replacing 245/75R16. 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.

245/75R16 vs 235/65R18 differences
Measurement	245/75R16	235/65R18	Difference	% diff
Overall diameter	30.47 in (773.9 mm)	30.03 in (762.7 mm)	−0.44 in (−11.2 mm)	−1.45%
Sidewall height	7.23 in (183.8 mm)	6.01 in (152.8 mm)	−1.22 in (−31.0 mm)	−16.87%
Section width	9.65 in (245.0 mm)	9.25 in (235.0 mm)	−0.39 in (−10.0 mm)	−4.08%
Circumference	95.72 in (2,431.3 mm)	94.33 in (2,396.1 mm)	−1.39 in (−35.2 mm)	−1.45%
Revolutions per mile	662	672	+10	+1.47%

True speed with the speedometer calibrated for 245/75R16
Indicated	Actual on 245/75R16	Actual on 235/65R18	Difference
30 mph	30.0 mph	29.6 mph	−0.4 mph
60 mph	60.0 mph	59.1 mph	−0.9 mph
75 mph	75.0 mph	73.9 mph	−1.1 mph

Ride-height change: 235/65R18 lowers the vehicle by 0.22 in (5.6 mm) at the axle (half the −11.2 mm diameter difference).

235/65R18 is 0.44 in shorter than 245/75R16 and 10 mm narrower, a 1.45% difference in overall diameter.

With the speedometer calibrated for 245/75R16, an indicated 60 mph is actually 59.1 mph on 235/65R18, and revolutions per mile change from 662 to 672.

235/65R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 245/75R16.

Size pages

Other comparisons with 245/75R16

Other comparisons with 235/65R18

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