235/40 R18 vs 245/45 R17

245/45 R17 stays within the configured tolerance for 235/40 R18: +1.1% diameter and +1.1% speedometer effect.

Geometric comparison

245/45 R17 stays within the configured tolerance for 235/40 R18: +1.1% diameter and +1.1% speedometer effect.

Geometric comparison
Metric	This size: 235/40 R18	Alternative: 245/45 R17	Difference	Verdict
Overall diameter	25.40 in	25.68 in	+1.1%	Within tolerance
Section width	9.25 in	9.65 in	+0.39 in	Computed difference
Sidewall height	3.70 in	4.34 in	+0.64 in	Computed difference
Circumference	79.80 in	80.68 in	+1.1%	Within tolerance
Speedo	0.0%	+1.1%	+1.1%	Within tolerance

Compare sizes

Current tireLooks valid

New tireLooks valid

Market

Units

Requires verificationWithin tolerance · Diameter +1.1% (+0.28 in) · US (~3%)

Requires verification · This rating covers tire geometry only, not vehicle compatibility.
Diameter +1.1% · Ride-height change +0.14 in.
Speedometer reads low · 60 mph → 60.7 mph.
Sidewall +0.64 in · Width +0.39 in.

Diameter+1.1%+0.28 in

Speedo @ 60+1.1%60 mph → 60.7 mph

Sidewall+0.64 inWidth +0.39 in

Ride-height change+0.14 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: 25.40 in 25.68 in+0.28 in
Sidewall: 3.70 in 4.34 in+0.64 in
Width: 9.25 in 9.65 in+0.39 in
Circumference: 79.80 in 80.68 in+1.1%
Revs / mile: 794 785
Speedo @ 60: 60 mph 60.7 mph+1.1%
Ride-height change: 0.00 in +0.14 in
True distance per 100 indicated: 100 mi 101.1 mi+1.1%

Current — 235/40 R18
New — 245/45 R17
Grounded to the road: the axle rises +0.14 in.

Result report

235/40 R18 245/45 R17 · Requires verification · Within tolerance

Plan budget for this size: 245/45 R17

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Plan budget for this size

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Markdown link

[235/40 R18 vs 245/45 R17 Tire size comparison](https://tirefitlab.com/tire-size-calculator/?from=235%2F40+R18&to=245%2F45+R17&market=us)

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Budget$80–$115Per tire Mid-range$110–$150Per tire Premium$155–$215Per 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 `235/40R18`	+0.0%	+0.0%

235/40 R18 · 245/45 R17 · Methodology

Technical check: 2026-06-28

What changed

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

Methodology