275/40 R20 vs 255/55 R18

255/55 R18 stays within the configured tolerance for 275/40 R20: +1.3% diameter and +1.3% speedometer effect.

Geometric comparison

255/55 R18 stays within the configured tolerance for 275/40 R20: +1.3% diameter and +1.3% speedometer effect.

Geometric comparison
Metric	This size: 275/40 R20	Alternative: 255/55 R18	Difference	Verdict
Overall diameter	28.66 in	29.04 in	+1.3%	Within tolerance
Section width	10.83 in	10.04 in	-0.79 in	Computed difference
Sidewall height	4.33 in	5.52 in	+1.19 in	Computed difference
Circumference	90.04 in	91.24 in	+1.3%	Within tolerance
Speedo	0.0%	+1.3%	+1.3%	Within tolerance

Compare sizes

Current tireLooks valid

New tireLooks valid

Market

Units

High fitment riskWithin tolerance · Diameter +1.3% (+0.38 in) · US (~3%)

High fitment risk · This rating covers tire geometry only, not vehicle compatibility.
Diameter +1.3% · Ride-height change +0.19 in.
Speedometer reads low · 60 mph → 60.8 mph.
Sidewall +1.19 in · Width -0.79 in.

Diameter+1.3%+0.38 in

Speedo @ 60+1.3%60 mph → 60.8 mph

Sidewall+1.19 inWidth -0.79 in

Ride-height change+0.19 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: 28.66 in 29.04 in+0.38 in
Sidewall: 4.33 in 5.52 in+1.19 in
Width: 10.83 in 10.04 in-0.79 in
Circumference: 90.04 in 91.24 in+1.3%
Revs / mile: 704 694
Speedo @ 60: 60 mph 60.8 mph+1.3%
Ride-height change: 0.00 in +0.19 in
True distance per 100 indicated: 100 mi 101.3 mi+1.3%

Current — 275/40 R20
New — 255/55 R18
Grounded to the road: the axle rises +0.19 in.

Result report

275/40 R20 255/55 R18 · High fitment risk · Within tolerance

Copy/print uses this page state only; TireFitLab does not create an account or store a server-side report.

Embed or cite this result

HTML iframe

<iframe src="https://tirefitlab.com/embed/tire-comparison/?from=275%2F40+R20&to=255%2F55+R18&market=us" title="275/40 R20 vs 255/55 R18 Tire size comparison" loading="lazy" width="720" height="330" style="width:100%;max-width:720px;border:0" referrerpolicy="strict-origin-when-cross-origin"></iframe>

Markdown link

[275/40 R20 vs 255/55 R18 Tire size comparison](https://tirefitlab.com/tire-size-calculator/?from=275%2F40+R20&to=255%2F55+R18&market=us)

Open embed preview

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 `275/40R20`	+0.0%	+0.0%

275/40 R20 · 255/55 R18 · Methodology

Technical check: 2026-06-28

What changed

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

Methodology