235/85R16 vs 275/65R18

275/65R18 is 0.35 in (8.8 mm) taller than 235/85R16, a +1.09% diameter difference. With the speedometer set for 235/85R16, an indicated 60 mph is 60.7 mph on 275/65R18.

Is this a safe swap?

Diameter difference +1.09%: within the ±3% guideline

By overall diameter alone, 275/65R18 falls inside the ±3% range commonly used as a guideline when replacing 235/85R16. 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.

235/85R16 vs 275/65R18 differences
Measurement	235/85R16	275/65R18	Difference	% diff
Overall diameter	31.73 in (805.9 mm)	32.07 in (814.7 mm)	+0.35 in (+8.8 mm)	+1.09%
Sidewall height	7.86 in (199.8 mm)	7.04 in (178.8 mm)	−0.83 in (−21.0 mm)	−10.51%
Section width	9.25 in (235.0 mm)	10.83 in (275.0 mm)	+1.57 in (+40.0 mm)	+17.02%
Circumference	99.68 in (2,531.8 mm)	100.77 in (2,559.5 mm)	+1.09 in (+27.6 mm)	+1.09%
Revolutions per mile	636	629	−7	−1.08%

True speed with the speedometer calibrated for 235/85R16
Indicated	Actual on 235/85R16	Actual on 275/65R18	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.7 mph	+0.7 mph
75 mph	75.0 mph	75.8 mph	+0.8 mph

Ride-height change: 275/65R18 raises the vehicle by 0.17 in (4.4 mm) at the axle (half the +8.8 mm diameter difference).

275/65R18 is 0.35 in taller than 235/85R16 and 40 mm wider, a 1.09% difference in overall diameter.

With the speedometer calibrated for 235/85R16, an indicated 60 mph is actually 60.7 mph on 275/65R18, and revolutions per mile change from 636 to 629.

275/65R18 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 275/65R18

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