215/55R18 vs 225/55R18

225/55R18 is 0.43 in (11.0 mm) taller than 215/55R18, a +1.59% diameter difference. With the speedometer set for 215/55R18, an indicated 60 mph is 61.0 mph on 225/55R18.

Is this a safe swap?

Diameter difference +1.59%: within the ±3% guideline

By overall diameter alone, 225/55R18 falls inside the ±3% range commonly used as a guideline when replacing 215/55R18. 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.

215/55R18 vs 225/55R18 differences
Measurement	215/55R18	225/55R18	Difference	% diff
Overall diameter	27.31 in (693.7 mm)	27.74 in (704.7 mm)	+0.43 in (+11.0 mm)	+1.59%
Sidewall height	4.66 in (118.3 mm)	4.87 in (123.8 mm)	+0.22 in (+5.5 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	85.80 in (2,179.3 mm)	87.16 in (2,213.9 mm)	+1.36 in (+34.6 mm)	+1.59%
Revolutions per mile	738	727	−12	−1.56%

True speed with the speedometer calibrated for 215/55R18
Indicated	Actual on 215/55R18	Actual on 225/55R18	Difference
30 mph	30.0 mph	30.5 mph	+0.5 mph
60 mph	60.0 mph	61.0 mph	+1.0 mph
75 mph	75.0 mph	76.2 mph	+1.2 mph

Ride-height change: 225/55R18 raises the vehicle by 0.22 in (5.5 mm) at the axle (half the +11.0 mm diameter difference).

225/55R18 is 0.43 in taller than 215/55R18 and 10 mm wider, a 1.59% difference in overall diameter.

With the speedometer calibrated for 215/55R18, an indicated 60 mph is actually 61.0 mph on 225/55R18, and revolutions per mile change from 738 to 727.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 215/55R18

Other comparisons with 225/55R18

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