255/40 R19 vs 235/50 R18

235/50 R18 stays within the configured tolerance for 255/40 R19: +0.8% diameter and +0.8% speedometer effect.

Geometric comparison

235/50 R18 stays within the configured tolerance for 255/40 R19: +0.8% diameter and +0.8% speedometer effect.

Geometric comparison
Metric	This size: 255/40 R19	Alternative: 235/50 R18	Difference	Verdict
Overall diameter	27.03 in	27.25 in	+0.8%	Within tolerance
Section width	10.04 in	9.25 in	-0.79 in	Computed difference
Sidewall height	4.02 in	4.63 in	+0.61 in	Computed difference
Circumference	84.92 in	85.61 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% (+0.22 in) · US (~3%)

Requires verification · This rating covers tire geometry only, not vehicle compatibility.
Diameter +0.8% · Ride-height change +0.11 in.
Speedometer reads low · 60 mph → 60.5 mph.
Sidewall +0.61 in · Width -0.79 in.

Diameter+0.8%+0.22 in

Speedo @ 60+0.8%60 mph → 60.5 mph

Sidewall+0.61 inWidth -0.79 in

Ride-height change+0.11 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: 27.03 in 27.25 in+0.22 in
Sidewall: 4.02 in 4.63 in+0.61 in
Width: 10.04 in 9.25 in-0.79 in
Circumference: 84.92 in 85.61 in+0.8%
Revs / mile: 746 740
Speedo @ 60: 60 mph 60.5 mph+0.8%
Ride-height change: 0.00 in +0.11 in
True distance per 100 indicated: 100 mi 100.8 mi+0.8%

Current — 255/40 R19
New — 235/50 R18
Grounded to the road: the axle rises +0.11 in.

Result report

255/40 R19 235/50 R18 · Requires verification · Within tolerance

Plan budget for this size: 235/50 R18

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Plan budget for this size

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Markdown link

[255/40 R19 vs 235/50 R18 Tire size comparison](https://tirefitlab.com/tire-size-calculator/?from=255%2F40+R19&to=235%2F50+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
−1″ `255/45R18`	+0.0%	+0.0%
OE `255/40R19`	+0.0%	+0.0%
+1″ `255/35R20`	-0.0%	-0.0%

255/40 R19 · 235/50 R18 · Methodology

Technical check: 2026-06-28

What changed

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

Methodology