Shopify Bicycle Bottom Bracket Schema — BSA vs BB30 vs PF30 vs BB86 vs T47 Shell Standards, Shimano 24mm vs SRAM DUB vs GXP Spindle Incompatibility

Bottom Bracket Shell Standards: Dimensions and Threading

Shell Standard Reference Table

BSA threads: the drive-side cup threads in left-hand (counterclockwise to tighten) to resist loosening under pedaling torque. The non-drive cup is right-hand threaded. This is opposite to intuition and is the source of many installation errors. Italian thread standard uses right-hand thread on both sides.

BB30 vs PF30: Same Bearings, Different Shell Width

BB30 and PF30 use identical bearings (30mm spindle ID × 42mm frame bore OD × 7mm wide). The shell bore is the same 42mm ID. The only difference is shell width: 68mm (BB30) vs 73mm (PF30). A PF30 bottom bracket assembly with a 68mm outer span will be loose in a PF30 frame's 73mm shell — the bearing cups will not press flush against both shell faces simultaneously. Always check shell width, not just bore ID.

Spindle Systems: The Second Compatibility Gate

After confirming shell standard, the spindle system (crankset's spindle diameter and design) determines which BB cups are required. Shell standard and spindle system are independent variables — a BSA-threaded shell can accept Shimano 24mm, SRAM DUB, or SRAM GXP cranks, each requiring different cups. Listing only "BSA compatible" without specifying the spindle system leaves the crankset-BB pairing ambiguous.

Spindle System Reference

BSA Frame: Which BB Cups Per Spindle

Press-Fit Creak: Cause, Mechanism, and Permanent Fix

Press-fit bottom brackets are the most complained-about component in modern cycling. The creak typically appears within 100–500 miles and worsens over time. Understanding why it happens reveals why the "permanent" fix works.

The Fretting Mechanism

A press-fit bearing is held in the frame shell by interference fit — the bearing outer race OD is slightly larger than the shell bore ID, so it must be pressed in with a tool. The interference fit (typically 0.01–0.05mm) creates a friction contact between the steel bearing outer race and the aluminum or carbon frame shell bore. Under pedaling load, the crank applies a torsional force through the spindle. This torque creates a cyclic alternating load on each bearing — the load direction reverses with each pedal stroke. At the bearing-to-shell interface, this cyclic loading causes micro-slip (fretting) at the contact surface. Even 1–5 microns of movement is enough to produce the creak sound. Grease at the interface reduces but does not eliminate fretting because it cannot prevent the micro-motion itself.

Shell Material and Creak Severity

Permanent Fix: Threaded T47 Adapters

The T47 threaded adapter (e.g., Wheels Mfg T47-BB86, CeramicSpeed T47 for PF30) presses into the existing press-fit shell bore and provides internal M47×1.0 threading. Once installed, standard T47 threaded bottom bracket cups thread into the adapter. The threaded engagement eliminates the fretting interface — the BB cup is now in threaded contact with the adapter, not pressed into the shell. These adapters are a one-time installation; the BB cups can be removed and replaced normally thereafter. Many mechanics now install T47 adapters in new carbon press-fit frames as a preventive measure before any creak develops.

Complete Bottom Bracket Schema — Shopify Liquid + Metafields

Metafield Namespace — bb.*

Shopify Liquid Snippet

{% assign bb = product.metafields.bb %}
{% if bb.shell_standard %}
<script type="application/ld+json">
{
  "@context": "https://schema.org",
  "@type": "Product",
  "name": {{ product.title | json }},
  "description": {{ product.description | strip_html | json }},
  "offers": { "@type": "Offer", "availability": "{% if product.available %}https://schema.org/InStock{% else %}https://schema.org/OutOfStock{% endif %}" },
  "additionalProperty": [
    { "@type": "PropertyValue", "name": "bb.shell_standard", "value": "{{ bb.shell_standard }}" },
    { "@type": "PropertyValue", "name": "bb.shell_width_mm", "value": "{{ bb.shell_width_mm }}" },
    { "@type": "PropertyValue", "name": "bb.shell_type", "value": "{{ bb.shell_type }}" },
    { "@type": "PropertyValue", "name": "bb.spindle_system", "value": "{{ bb.spindle_system }}" },
    { "@type": "PropertyValue", "name": "bb.spindle_diameter_mm", "value": "{{ bb.spindle_diameter_mm }}" },
    { "@type": "PropertyValue", "name": "bb.bore_id_mm", "value": "{{ bb.bore_id_mm }}" },
    { "@type": "PropertyValue", "name": "bb.bearing_type", "value": "{{ bb.bearing_type }}" }
  ]
}
</script>
{% endif %}

5 Critical Bottom Bracket Schema Mistakes

1. Listing shell standard without spindle system. "BSA compatible" describes the frame shell but leaves the crankset spindle open — a BSA-threaded shell requires different cups for Shimano 24mm, SRAM DUB, SRAM GXP, and BB30-spindle cranks. "BSA compatible" without spindle_system is approximately 25% of the information needed to determine actual compatibility.
2. Conflating BB30 and PF30 as the same standard. Both use identical 42mm bore ID bearings but different shell widths (68mm vs 73mm). A BB30-spec bottom bracket assembly installed in a PF30 frame will have a 5mm gap and unsupported bearing face on one side.
3. Missing GXP side-specific warning. SRAM GXP bottom bracket cups have different bearing bore diameters on each side (24mm non-drive, 22mm drive) and cannot be installed reversed. A product listing for a "SRAM GXP BSA bottom bracket" without the side-specific flag allows installation errors causing immediate bearing failure.
4. Describing SRAM DUB as "24mm compatible." SRAM DUB uses a 28.99mm spindle — not 24mm. DUB marketing materials describe the standard as "universal," which causes AI agents to incorrectly match DUB cranks with 24mm Shimano-compatible cups. Encode bb.spindle_system: "sram-dub" as a distinct value from "shimano-24mm".
5. Omitting press-fit vs threaded distinction. Press-fit BB installations carry a known creak risk that threaded installations do not. A buyer choosing between a press-fit BB and a T47 adapter kit for a PF30 frame is making a meaningful decision — without bb.shell_type, an AI agent cannot distinguish these categories.

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