235/60R16 vs 255/45R18

255/45R18 is 0.07 in (1.7 mm) shorter than 235/60R16, a −0.25% diameter difference. With the speedometer set for 235/60R16, an indicated 60 mph is 59.9 mph on 255/45R18.

Is this a safe swap?

Diameter difference −0.25%: under 1%

By overall diameter alone, 255/45R18 is a near match for 235/60R16; 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.

235/60R16 vs 255/45R18 differences
Measurement	235/60R16	255/45R18	Difference	% diff
Overall diameter	27.10 in (688.4 mm)	27.04 in (686.7 mm)	−0.07 in (−1.7 mm)	−0.25%
Sidewall height	5.55 in (141.0 mm)	4.52 in (114.8 mm)	−1.03 in (−26.2 mm)	−18.62%
Section width	9.25 in (235.0 mm)	10.04 in (255.0 mm)	+0.79 in (+20.0 mm)	+8.51%
Circumference	85.14 in (2,162.7 mm)	84.93 in (2,157.3 mm)	−0.21 in (−5.3 mm)	−0.25%
Revolutions per mile	744	746	+2	+0.25%

True speed with the speedometer calibrated for 235/60R16
Indicated	Actual on 235/60R16	Actual on 255/45R18	Difference
30 mph	30.0 mph	29.9 mph	−0.1 mph
60 mph	60.0 mph	59.9 mph	−0.1 mph
75 mph	75.0 mph	74.8 mph	−0.2 mph

Ride-height change: 255/45R18 lowers the vehicle by 0.03 in (0.8 mm) at the axle (half the −1.7 mm diameter difference).

255/45R18 is 0.07 in shorter than 235/60R16 and 20 mm wider, a 0.25% difference in overall diameter.

With the speedometer calibrated for 235/60R16, an indicated 60 mph is actually 59.9 mph on 255/45R18, and revolutions per mile change from 744 to 746.

255/45R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 235/60R16.

Size pages

Other comparisons with 235/60R16

Other comparisons with 255/45R18

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