225/60R16 vs 235/45R18

235/45R18 is 0.30 in (7.7 mm) shorter than 225/60R16, a −1.14% diameter difference. With the speedometer set for 225/60R16, an indicated 60 mph is 59.3 mph on 235/45R18.

Is this a safe swap?

Diameter difference −1.14%: within the ±3% guideline

By overall diameter alone, 235/45R18 falls inside the ±3% range commonly used as a guideline when replacing 225/60R16. 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.

225/60R16 vs 235/45R18 differences
Measurement	225/60R16	235/45R18	Difference	% diff
Overall diameter	26.63 in (676.4 mm)	26.33 in (668.7 mm)	−0.30 in (−7.7 mm)	−1.14%
Sidewall height	5.31 in (135.0 mm)	4.16 in (105.8 mm)	−1.15 in (−29.2 mm)	−21.67%
Section width	8.86 in (225.0 mm)	9.25 in (235.0 mm)	+0.39 in (+10.0 mm)	+4.44%
Circumference	83.66 in (2,125.0 mm)	82.71 in (2,100.8 mm)	−0.95 in (−24.2 mm)	−1.14%
Revolutions per mile	757	766	+9	+1.15%

True speed with the speedometer calibrated for 225/60R16
Indicated	Actual on 225/60R16	Actual on 235/45R18	Difference
30 mph	30.0 mph	29.7 mph	−0.3 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: 235/45R18 lowers the vehicle by 0.15 in (3.8 mm) at the axle (half the −7.7 mm diameter difference).

235/45R18 is 0.30 in shorter than 225/60R16 and 10 mm wider, a 1.14% difference in overall diameter.

With the speedometer calibrated for 225/60R16, an indicated 60 mph is actually 59.3 mph on 235/45R18, and revolutions per mile change from 757 to 766.

235/45R18 mounts on a 18-inch wheel, a plus-2 fitment from the 16-inch wheel of 225/60R16.

Size pages

Other comparisons with 225/60R16

Other comparisons with 235/45R18

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