215/45R18 vs 235/45R18

235/45R18 is 0.71 in (18.0 mm) taller than 215/45R18, a +2.77% diameter difference. With the speedometer set for 215/45R18, an indicated 60 mph is 61.7 mph on 235/45R18.

Is this a safe swap?

Diameter difference +2.77%: within the ±3% guideline

By overall diameter alone, 235/45R18 falls inside the ±3% range commonly used as a guideline when replacing 215/45R18. 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.

215/45R18 vs 235/45R18 differences
Measurement	215/45R18	235/45R18	Difference	% diff
Overall diameter	25.62 in (650.7 mm)	26.33 in (668.7 mm)	+0.71 in (+18.0 mm)	+2.77%
Sidewall height	3.81 in (96.8 mm)	4.16 in (105.8 mm)	+0.35 in (+9.0 mm)	+9.30%
Section width	8.46 in (215.0 mm)	9.25 in (235.0 mm)	+0.79 in (+20.0 mm)	+9.30%
Circumference	80.48 in (2,044.2 mm)	82.71 in (2,100.8 mm)	+2.23 in (+56.5 mm)	+2.77%
Revolutions per mile	787	766	−21	−2.69%

True speed with the speedometer calibrated for 215/45R18
Indicated	Actual on 215/45R18	Actual on 235/45R18	Difference
30 mph	30.0 mph	30.8 mph	+0.8 mph
60 mph	60.0 mph	61.7 mph	+1.7 mph
75 mph	75.0 mph	77.1 mph	+2.1 mph

Ride-height change: 235/45R18 raises the vehicle by 0.35 in (9.0 mm) at the axle (half the +18.0 mm diameter difference).

235/45R18 is 0.71 in taller than 215/45R18 and 20 mm wider, a 2.77% difference in overall diameter.

With the speedometer calibrated for 215/45R18, an indicated 60 mph is actually 61.7 mph on 235/45R18, and revolutions per mile change from 787 to 766.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 215/45R18

Other comparisons with 235/45R18

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