245/45 R18 vs 255/40 R19

255/40 R19 stays within the configured tolerance for 245/45 R18: +1.3% diameter and +1.3% speedometer effect.

Geometric comparison

255/40 R19 stays within the configured tolerance for 245/45 R18: +1.3% diameter and +1.3% speedometer effect.

Geometric comparison
Metric	This size: 245/45 R18	Alternative: 255/40 R19	Difference	Verdict
Overall diameter	26.68 in	27.03 in	+1.3%	Within tolerance
Section width	9.65 in	10.04 in	+0.39 in	Computed difference
Sidewall height	4.34 in	4.02 in	-0.32 in	Computed difference
Circumference	83.82 in	84.92 in	+1.3%	Within tolerance
Speedo	0.0%	+1.3%	+1.3%	Within tolerance

Compare sizes

Current tireLooks valid

New tireLooks valid

Market

Units

Minor variationWithin tolerance · Diameter +1.3% (+0.35 in) · US (~3%)

Minor variation · This rating covers tire geometry only, not vehicle compatibility.
Diameter +1.3% · Ride-height change +0.18 in.
Speedometer reads low · 60 mph → 60.8 mph.
Sidewall -0.32 in · Width +0.39 in.

Diameter+1.3%+0.35 in

Speedo @ 60+1.3%60 mph → 60.8 mph

Sidewall-0.32 inWidth +0.39 in

Ride-height change+0.18 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: 26.68 in 27.03 in+0.35 in
Sidewall: 4.34 in 4.02 in-0.32 in
Width: 9.65 in 10.04 in+0.39 in
Circumference: 83.82 in 84.92 in+1.3%
Revs / mile: 756 746
Speedo @ 60: 60 mph 60.8 mph+1.3%
Ride-height change: 0.00 in +0.18 in
True distance per 100 indicated: 100 mi 101.3 mi+1.3%

Current — 245/45 R18
New — 255/40 R19
Grounded to the road: the axle rises +0.18 in.

Result report

245/45 R18 255/40 R19 · Minor variation · Within tolerance

Plan budget for this size: 255/40 R19

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Plan budget for this size

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Markdown link

[245/45 R18 vs 255/40 R19 Tire size comparison](https://tirefitlab.com/tire-size-calculator/?from=245%2F45+R18&to=255%2F40+R19&market=us)

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Budget$125–$175Per tire Mid-range$160–$230Per tire Premium$230–$325Per 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 `245/45R18`	+0.0%	+0.0%

245/45 R18 · 255/40 R19 · Methodology

Technical check: 2026-06-28

What changed

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

Methodology