215/85R16 vs 235/65R18

235/65R18 is 0.36 in (9.2 mm) shorter than 215/85R16, a −1.19% diameter difference. With the speedometer set for 215/85R16, an indicated 60 mph is 59.3 mph on 235/65R18.

Is this a safe swap?

Diameter difference −1.19%: within the ±3% guideline

By overall diameter alone, 235/65R18 falls inside the ±3% range commonly used as a guideline when replacing 215/85R16. 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.

215/85R16 vs 235/65R18 differences
Measurement	215/85R16	235/65R18	Difference	% diff
Overall diameter	30.39 in (771.9 mm)	30.03 in (762.7 mm)	−0.36 in (−9.2 mm)	−1.19%
Sidewall height	7.19 in (182.8 mm)	6.01 in (152.8 mm)	−1.18 in (−30.0 mm)	−16.42%
Section width	8.46 in (215.0 mm)	9.25 in (235.0 mm)	+0.79 in (+20.0 mm)	+9.30%
Circumference	95.47 in (2,425.0 mm)	94.33 in (2,396.1 mm)	−1.14 in (−28.9 mm)	−1.19%
Revolutions per mile	664	672	+8	+1.21%

True speed with the speedometer calibrated for 215/85R16
Indicated	Actual on 215/85R16	Actual on 235/65R18	Difference
30 mph	30.0 mph	29.6 mph	−0.4 mph
60 mph	60.0 mph	59.3 mph	−0.7 mph
75 mph	75.0 mph	74.1 mph	−0.9 mph

Ride-height change: 235/65R18 lowers the vehicle by 0.18 in (4.6 mm) at the axle (half the −9.2 mm diameter difference).

235/65R18 is 0.36 in shorter than 215/85R16 and 20 mm wider, a 1.19% difference in overall diameter.

With the speedometer calibrated for 215/85R16, an indicated 60 mph is actually 59.3 mph on 235/65R18, and revolutions per mile change from 664 to 672.

235/65R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 215/85R16.

Size pages

Other comparisons with 215/85R16

Other comparisons with 235/65R18

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