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.

Geometric comparison

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

Geometric comparison
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

Compare sizes

Current tireLooks valid

New tireLooks valid

Market

Units

Requires verificationWithin tolerance · Diameter +0.8% (+0.21 in) · US (~3%)

Requires verification · This rating covers tire geometry only, not vehicle compatibility.
Diameter +0.8% · Ride-height change +0.10 in.
Speedometer reads low · 60 mph → 60.5 mph.
Sidewall -0.90 in · Width +0.79 in.

Diameter+0.8%+0.21 in

Speedo @ 60+0.8%60 mph → 60.5 mph

Sidewall-0.90 inWidth +0.79 in

Ride-height change+0.10 inDiameter ÷ 2

How this result is calculated

Computed from nominal tire-size geometry: diameter, circumference and speedometer error. It does not check vehicle placard approval, load/speed rating, rim-width range, wheel-arch, suspension or brake clearance.

Methodology

Before fitting

Check the vehicle placard and owner’s manual first.
Match or exceed the required load index and speed rating.
Confirm rim-width range, bolt pattern, hub bore, offset and fasteners.
Inspect wheel-arch, suspension and brake clearance under real vehicle load.
Check TPMS, cold pressure and local roadworthiness rules.

Diameter: 24.88 in 25.09 in+0.21 in
Sidewall: 4.44 in 3.54 in-0.90 in
Width: 8.07 in 8.86 in+0.79 in
Circumference: 78.16 in 78.81 in+0.8%
Revs / mile: 811 804
Speedo @ 60: 60 mph 60.5 mph+0.8%
Ride-height change: 0.00 in +0.10 in
True distance per 100 indicated: 100 mi 100.8 mi+0.8%

Current — 205/55 R16
New — 225/40 R18
Grounded to the road: the axle rises +0.10 in.

Result report

205/55 R16 225/40 R18 · Requires verification · Within tolerance

Plan budget for this size: 225/40 R18

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Plan budget for this size

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Markdown link

[205/55 R16 vs 225/40 R18 Tire size comparison](https://tirefitlab.com/tire-size-calculator/?from=205%2F55+R16&to=225%2F40+R18&market=us)

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Budget$85–$120Per tire Mid-range$110–$160Per tire Premium$160–$225Per tire

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

In-tolerance alternative sizes

In-tolerance alternative sizes
Size	Diameter	Speedo @ 100	Use this
OE `205/55R16`	+0.0%	+0.0%

205/55 R16 · 225/40 R18 · Methodology

Technical check: 2026-06-28

What changed

Checked generated routes, metadata, sitemap inclusion and localized page rendering.

Methodology