205/55 R16 vs 225/40 R18

225/40 R18 stays within the configured tolerance for 205/55 R16: +0.8% diameter and +0.8% speedometer effect.

Fitment verdict

225/40 R18 stays within the configured tolerance for 205/55 R16: +0.8% diameter and +0.8% speedometer effect.

Metric	This size: 205/55 R16	Alternative: 225/40 R18	Difference	Verdict
Overall diameter	24.88 in	25.09 in	+0.8%	Within tolerance
Section width	8.07 in	8.86 in	+0.79 in	Computed difference
Sidewall height	4.44 in	3.54 in	-0.90 in	Computed difference
Circumference	78.16 in	78.81 in	+0.8%	Within tolerance
Speedo	0.0%	+0.8%	+0.8%	Within tolerance

Current tireLooks valid

New tireLooks valid

Market

Units

✓ Within toleranceDiameter +0.8% (+0.21 in) · US (~3%)

Diameter+0.8%+0.21 in

Speedo @ 60+0.8%60 mph → 60.5 mph

Sidewall-0.90 inWidth +0.79 in

How this result is calculated

Computed from nominal tire-size geometry: diameter, circumference and speedometer error. It does not check wheel-arch, suspension or brake clearance.

205/55 R16 225/40 R18 · Within tolerance

Use this size when shopping: 225/40 R18

Geometric estimate. Always verify physical clearance (arches, suspension, brakes) before fitting.

Size	Diameter	Speedo @ 100
−1″ `315/40R15`	+0.2%	+0.2%
OE `205/55R16`	+0.0%	+0.0%
+1″ `125/80R17`	-0.0%	-0.0%
+2″ `125/70R18`	+0.0%	+0.0%

What changed

Reviewed deterministic geometry, load/speed references, sitemap inclusion and localized page shell.