31x10.50 R15 vs 265/65 R18

265/65 R18 stays within the configured tolerance for 31x10.50 R15: +1.8% diameter and +1.8% speedometer effect.

Geometric comparison

265/65 R18 stays within the configured tolerance for 31x10.50 R15: +1.8% diameter and +1.8% speedometer effect.

Geometric comparison
Metric	This size: 31x10.50 R15	Alternative: 265/65 R18	Difference	Verdict
Overall diameter	31.00 in	31.56 in	+1.8%	Within tolerance
Section width	10.50 in	10.43 in	-0.07 in	Computed difference
Sidewall height	8.00 in	6.78 in	-1.22 in	Computed difference
Circumference	97.39 in	99.16 in	+1.8%	Within tolerance
Speedo	0.0%	+1.8%	+1.8%	Within tolerance

Compare sizes

Current tireLooks valid

New tireLooks valid

Market

Units

High fitment riskWithin tolerance · Diameter +1.8% (+0.56 in) · US (~3%)

High fitment risk · This rating covers tire geometry only, not vehicle compatibility.
Diameter +1.8% · Ride-height change +0.28 in.
Speedometer reads low · 60 mph → 61.1 mph.
Sidewall -1.22 in · Width -0.07 in.

Diameter+1.8%+0.56 in

Speedo @ 60+1.8%60 mph → 61.1 mph

Sidewall-1.22 inWidth -0.07 in

Ride-height change+0.28 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: 31.00 in 31.56 in+0.56 in
Sidewall: 8.00 in 6.78 in-1.22 in
Width: 10.50 in 10.43 in-0.07 in
Circumference: 97.39 in 99.16 in+1.8%
Revs / mile: 651 639
Speedo @ 60: 60 mph 61.1 mph+1.8%
Ride-height change: 0.00 in +0.28 in
True distance per 100 indicated: 100 mi 101.8 mi+1.8%

Current — 31x10.50 R15
New — 265/65 R18
Grounded to the road: the axle rises +0.28 in.

Result report

31x10.50 R15 265/65 R18 · High fitment risk · Within tolerance

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Markdown link

[31x10.50 R15 vs 265/65 R18 Tire size comparison](https://tirefitlab.com/tire-size-calculator/?from=31x10.50+R15&to=265%2F65+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
OE `255/80R15`	+0.2%	+0.2%

31x10.50 R15 · 265/65 R18 · Methodology

Technical check: 2026-06-28

What changed

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

Methodology