225/45R18 vs 235/45R18

235/45R18 is 0.35 in (9.0 mm) taller than 225/45R18, a +1.36% diameter difference. With the speedometer set for 225/45R18, an indicated 60 mph is 60.8 mph on 235/45R18.

Is this a safe swap?

Diameter difference +1.36%: within the ±3% guideline

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

225/45R18 vs 235/45R18 differences
Measurement	225/45R18	235/45R18	Difference	% diff
Overall diameter	25.97 in (659.7 mm)	26.33 in (668.7 mm)	+0.35 in (+9.0 mm)	+1.36%
Sidewall height	3.99 in (101.3 mm)	4.16 in (105.8 mm)	+0.18 in (+4.5 mm)	+4.44%
Section width	8.86 in (225.0 mm)	9.25 in (235.0 mm)	+0.39 in (+10.0 mm)	+4.44%
Circumference	81.59 in (2,072.5 mm)	82.71 in (2,100.8 mm)	+1.11 in (+28.3 mm)	+1.36%
Revolutions per mile	777	766	−10	−1.35%

True speed with the speedometer calibrated for 225/45R18
Indicated	Actual on 225/45R18	Actual on 235/45R18	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.8 mph	+0.8 mph
75 mph	75.0 mph	76.0 mph	+1.0 mph

Ride-height change: 235/45R18 raises the vehicle by 0.18 in (4.5 mm) at the axle (half the +9.0 mm diameter difference).

235/45R18 is 0.35 in taller than 225/45R18 and 10 mm wider, a 1.36% difference in overall diameter.

With the speedometer calibrated for 225/45R18, an indicated 60 mph is actually 60.8 mph on 235/45R18, and revolutions per mile change from 777 to 766.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 225/45R18

Other comparisons with 235/45R18

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