195/65 R15 vs 225/40 R18

225/40 R18 stays within the configured tolerance for 195/65 R15: +0.4% diameter and +0.4% speedometer effect.

Geometric comparison

225/40 R18 stays within the configured tolerance for 195/65 R15: +0.4% diameter and +0.4% speedometer effect.

Geometric comparison
Metric	This size: 195/65 R15	Alternative: 225/40 R18	Difference	Verdict
Overall diameter	24.98 in	25.09 in	+0.4%	Within tolerance
Section width	7.68 in	8.86 in	+1.18 in	Computed difference
Sidewall height	4.99 in	3.54 in	-1.45 in	Computed difference
Circumference	78.48 in	78.81 in	+0.4%	Within tolerance
Speedo	0.0%	+0.4%	+0.4%	Within tolerance

Compare sizes

Current tireLooks valid

New tireLooks valid

Market

Units

High fitment riskWithin tolerance · Diameter +0.4% (+0.11 in) · US (~3%)

High fitment risk · This rating covers tire geometry only, not vehicle compatibility.
Diameter +0.4% · Ride-height change +0.05 in.
Speedometer reads low · 60 mph → 60.3 mph.
Sidewall -1.45 in · Width +1.18 in.

Diameter+0.4%+0.11 in

Speedo @ 60+0.4%60 mph → 60.3 mph

Sidewall-1.45 inWidth +1.18 in

Ride-height change+0.05 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: 24.98 in 25.09 in+0.11 in
Sidewall: 4.99 in 3.54 in-1.45 in
Width: 7.68 in 8.86 in+1.18 in
Circumference: 78.48 in 78.81 in+0.4%
Revs / mile: 807 804
Speedo @ 60: 60 mph 60.3 mph+0.4%
Ride-height change: 0.00 in +0.05 in
True distance per 100 indicated: 100 mi 100.4 mi+0.4%

Current — 195/65 R15
New — 225/40 R18
Grounded to the road: the axle rises +0.05 in.

Result report

195/65 R15 225/40 R18 · High fitment risk · Within tolerance

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Markdown link

[195/65 R15 vs 225/40 R18 Tire size comparison](https://tirefitlab.com/tire-size-calculator/?from=195%2F65+R15&to=225%2F40+R18&market=us)

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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
−1″ `215/65R14`	+0.1%	+0.1%
OE `195/65R15`	+0.0%	+0.0%

195/65 R15 · 225/40 R18 · Methodology

Technical check: 2026-06-28

What changed

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

Methodology