215/45R18 vs 225/45R18

225/45R18 is 0.35 in (9.0 mm) taller than 215/45R18, a +1.38% diameter difference. With the speedometer set for 215/45R18, an indicated 60 mph is 60.8 mph on 225/45R18.

Is this a safe swap?

Diameter difference +1.38%: within the ±3% guideline

By overall diameter alone, 225/45R18 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 225/45R18 differences
Measurement	215/45R18	225/45R18	Difference	% diff
Overall diameter	25.62 in (650.7 mm)	25.97 in (659.7 mm)	+0.35 in (+9.0 mm)	+1.38%
Sidewall height	3.81 in (96.8 mm)	3.99 in (101.3 mm)	+0.18 in (+4.5 mm)	+4.65%
Section width	8.46 in (215.0 mm)	8.86 in (225.0 mm)	+0.39 in (+10.0 mm)	+4.65%
Circumference	80.48 in (2,044.2 mm)	81.59 in (2,072.5 mm)	+1.11 in (+28.3 mm)	+1.38%
Revolutions per mile	787	777	−11	−1.36%

True speed with the speedometer calibrated for 215/45R18
Indicated	Actual on 215/45R18	Actual on 225/45R18	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: 225/45R18 raises the vehicle by 0.18 in (4.5 mm) at the axle (half the +9.0 mm diameter difference).

225/45R18 is 0.35 in taller than 215/45R18 and 10 mm wider, a 1.38% difference in overall diameter.

With the speedometer calibrated for 215/45R18, an indicated 60 mph is actually 60.8 mph on 225/45R18, and revolutions per mile change from 787 to 777.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 215/45R18

Other comparisons with 225/45R18

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