245/65 R18 vs 31x10.50 R15

31x10.50 R15 stays within the configured tolerance for 245/65 R18: +1.5% diameter and +1.5% speedometer effect.

Geometric comparison

31x10.50 R15 stays within the configured tolerance for 245/65 R18: +1.5% diameter and +1.5% speedometer effect.

Geometric comparison
Metric	This size: 245/65 R18	Alternative: 31x10.50 R15	Difference	Verdict
Overall diameter	30.54 in	31.00 in	+1.5%	Within tolerance
Section width	9.65 in	10.50 in	+0.85 in	Computed difference
Sidewall height	6.27 in	8.00 in	+1.73 in	Computed difference
Circumference	95.94 in	97.39 in	+1.5%	Within tolerance
Speedo	0.0%	+1.5%	+1.5%	Within tolerance

Compare sizes

Current tireLooks valid

New tireLooks valid

Market

Units

Not recommendedWithin tolerance · Diameter +1.5% (+0.46 in) · US (~3%)

Not recommended · This rating covers tire geometry only, not vehicle compatibility.
Diameter +1.5% · Ride-height change +0.23 in.
Speedometer reads low · 60 mph → 60.9 mph.
Sidewall +1.73 in · Width +0.85 in.

Diameter+1.5%+0.46 in

Speedo @ 60+1.5%60 mph → 60.9 mph

Sidewall+1.73 inWidth +0.85 in

Ride-height change+0.23 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: 30.54 in 31.00 in+0.46 in
Sidewall: 6.27 in 8.00 in+1.73 in
Width: 9.65 in 10.50 in+0.85 in
Circumference: 95.94 in 97.39 in+1.5%
Revs / mile: 660 651
Speedo @ 60: 60 mph 60.9 mph+1.5%
Ride-height change: 0.00 in +0.23 in
True distance per 100 indicated: 100 mi 101.5 mi+1.5%

Current — 245/65 R18
New — 31x10.50 R15
Grounded to the road: the axle rises +0.23 in.

Result report

245/65 R18 31x10.50 R15 · Not recommended · Within tolerance

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Markdown link

[245/65 R18 vs 31x10.50 R15 Tire size comparison](https://tirefitlab.com/tire-size-calculator/?from=245%2F65+R18&to=31x10.50+R15&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″ `215/80R17`	+0.0%	+0.0%
OE `245/65R18`	+0.0%	+0.0%

245/65 R18 · 31x10.50 R15 · Methodology

Technical check: 2026-06-28

What changed

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

Methodology