275/60R17 vs 235/65R18

235/65R18 is 0.04 in (0.9 mm) taller than 275/60R17, a +0.12% diameter difference. With the speedometer set for 275/60R17, an indicated 60 mph is 60.1 mph on 235/65R18.

Is this a safe swap?

Diameter difference +0.12%: under 1%

By overall diameter alone, 235/65R18 is a near match for 275/60R17; 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.

275/60R17 vs 235/65R18 differences
Measurement	275/60R17	235/65R18	Difference	% diff
Overall diameter	29.99 in (761.8 mm)	30.03 in (762.7 mm)	+0.04 in (+0.9 mm)	+0.12%
Sidewall height	6.50 in (165.0 mm)	6.01 in (152.8 mm)	−0.48 in (−12.2 mm)	−7.42%
Section width	10.83 in (275.0 mm)	9.25 in (235.0 mm)	−1.57 in (−40.0 mm)	−14.55%
Circumference	94.22 in (2,393.3 mm)	94.33 in (2,396.1 mm)	+0.11 in (+2.8 mm)	+0.12%
Revolutions per mile	672	672	−1	−0.12%

True speed with the speedometer calibrated for 275/60R17
Indicated	Actual on 275/60R17	Actual on 235/65R18	Difference
30 mph	30.0 mph	30.0 mph	0.0 mph
60 mph	60.0 mph	60.1 mph	+0.1 mph
75 mph	75.0 mph	75.1 mph	+0.1 mph

Ride-height change: 235/65R18 raises the vehicle by 0.02 in (0.5 mm) at the axle (half the +0.9 mm diameter difference).

235/65R18 is 0.04 in taller than 275/60R17 and 40 mm narrower, a 0.12% difference in overall diameter.

With the speedometer calibrated for 275/60R17, an indicated 60 mph is actually 60.1 mph on 235/65R18, and revolutions per mile change from 672 to 672.

235/65R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 275/60R17.

Size pages

Other comparisons with 275/60R17

Other comparisons with 235/65R18

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