245/65R16 vs 235/55R18

235/55R18 is 0.36 in (9.2 mm) shorter than 245/65R16, a −1.27% diameter difference. With the speedometer set for 245/65R16, an indicated 60 mph is 59.2 mph on 235/55R18.

Is this a safe swap?

Diameter difference −1.27%: within the ±3% guideline

By overall diameter alone, 235/55R18 falls inside the ±3% range commonly used as a guideline when replacing 245/65R16. 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.

245/65R16 vs 235/55R18 differences
Measurement	245/65R16	235/55R18	Difference	% diff
Overall diameter	28.54 in (724.9 mm)	28.18 in (715.7 mm)	−0.36 in (−9.2 mm)	−1.27%
Sidewall height	6.27 in (159.3 mm)	5.09 in (129.3 mm)	−1.18 in (−30.0 mm)	−18.84%
Section width	9.65 in (245.0 mm)	9.25 in (235.0 mm)	−0.39 in (−10.0 mm)	−4.08%
Circumference	89.66 in (2,277.3 mm)	88.52 in (2,248.4 mm)	−1.14 in (−28.9 mm)	−1.27%
Revolutions per mile	707	716	+9	+1.29%

True speed with the speedometer calibrated for 245/65R16
Indicated	Actual on 245/65R16	Actual on 235/55R18	Difference
30 mph	30.0 mph	29.6 mph	−0.4 mph
60 mph	60.0 mph	59.2 mph	−0.8 mph
75 mph	75.0 mph	74.0 mph	−1.0 mph

Ride-height change: 235/55R18 lowers the vehicle by 0.18 in (4.6 mm) at the axle (half the −9.2 mm diameter difference).

235/55R18 is 0.36 in shorter than 245/65R16 and 10 mm narrower, a 1.27% difference in overall diameter.

With the speedometer calibrated for 245/65R16, an indicated 60 mph is actually 59.2 mph on 235/55R18, and revolutions per mile change from 707 to 716.

235/55R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 245/65R16.

Size pages

Other comparisons with 245/65R16

Other comparisons with 235/55R18

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