Shopify tire and wheel fitment schema for AI agents: the 2.3mm bolt pattern difference that causes wheel separation — and four more fitment dimensions no listing encodes

Bolt pattern notation: why both numbers must match exactly

Wheel bolt pattern — also called lug pattern or PCD pattern — uses a two-number notation: bolt count × pitch circle diameter. The pitch circle diameter (PCD) is the diameter in millimeters of the imaginary circle that passes through the center of all bolt holes. 5×114.3 means 5 bolts arranged on a 114.3mm-diameter circle. 5×112 means 5 bolts on a 112mm-diameter circle.

The bolt count is easy to verify visually. The PCD is invisible and routinely omitted from product titles, bullet points, and even full product descriptions in automotive aftermarket listings on Shopify. Many stores write "5-lug" or "5-bolt pattern" without specifying the PCD — which is the only number that determines physical fitment.

The 5×114.3 vs 5×112 failure mode, in detail

When you attempt to mount a 5×114.3 wheel on a 5×112 hub, each of the five studs on the hub falls 2.3mm outside its corresponding bolt hole in the wheel. Because the bolt holes are evenly spaced on a circle, no rotation of the wheel corrects this — the geometry is different, not offset. What makes this scenario dangerous rather than immediately obvious:

PCD reference table: 8 patterns that cover 90% of passenger vehicles

Aftermarket wheel manufacturers target a small set of PCDs that cover the majority of the passenger vehicle market. Understanding which PCDs appear on which brands and generations prevents the most common AI recommendation errors.

Center bore: hub-centric vs lug-centric — why 73mm universal wheels vibrate on Toyota hubs

Center bore is the diameter in millimeters of the circular hole in the center of the wheel. The vehicle's hub has a machined pilot flange — a raised cylinder of precise diameter — that the wheel center bore slides over during installation. For hub-centric fit, the wheel center bore must match the hub pilot diameter within 0.1mm tolerance.

Why hub centering matters more than lug nut torque

In hub-centric mounting, the hub pilot positions the wheel — the lug nuts provide clamping force to hold the wheel against the hub face, but the hub pilot geometry determines rotational centering. This is the most precise method: the hub is machined to closer tolerance than any lug nut taper seat.

In lug-centric mounting (wheel center bore larger than hub pilot), the lug nuts must do both jobs: clamp the wheel AND center it through their tapered seats. Even at the correct torque spec with quality lug nuts, lug-centric mounting is geometrically less precise than hub-centric. Under the cyclic loads of driving — rotation, lateral g-forces in corners, road surface inputs — microscopic variation in lug nut seating allows the wheel to shift fractionally relative to the hub center.

This shift manifests as vibration through the steering wheel. The characteristic signature: starts around 50–55 mph, peaks around 65–75 mph, sometimes decreases above 80 mph as the wheel re-centers under different force dynamics. Multiple tire balance jobs reduce but never eliminate the vibration — because the root cause is wheel centering, not mass balance. The correct fix is hub-centric rings.

The Toyota 60.1mm problem

Toyota uses a 60.1mm hub pilot diameter across virtually its entire lineup: Camry, Corolla, RAV4, Highlander, Tacoma, Tundra, Prius, most Lexus models. The most common aftermarket wheel center bore is 73mm, marketed as "universal fit." The math:

73mm bore − 60.1mm pilot = 12.9mm gap in diameter = 6.45mm radial gap on every side.

A 6.45mm gap between wheel bore and hub pilot is significant. Hub-centric rings for this combination are labeled 73→60.1mm, available at any wheel accessories retailer for a few dollars per ring. But if the listing doesn't encode wheel_tire.center_bore_mm, an AI agent recommending "universal fit" wheels for a Toyota buyer has no data to trigger the hub-ring recommendation.

Wheel offset ET: what Einpresstiefe controls and why ±10mm beyond OEM matters

ET comes from the German Einpresstiefe — literally "press-in depth." It is the signed distance in millimeters between the wheel's mounting face (the flat surface that contacts the hub) and the wheel's geometric centerline. It is one of the most commonly omitted fields in aftermarket wheel listings, and one of the most consequential for fit.

Positive, zero, and negative ET — what each controls

Positive ET (e.g., ET+45): The mounting face is on the road-facing side of the centerline. The wheel sits tucked toward the suspension and brakes. Most front-wheel drive and all-wheel drive cars use positive ET because the wheel must clear the inner suspension components of a transverse drivetrain.

Zero ET: The mounting face aligns exactly with the centerline. Used on some classic muscle cars and certain off-road applications where a neutral stance is specified.

Negative ET (e.g., ET−12): The mounting face is on the hub/brake side of the centerline. The wheel protrudes outward. Common on wide-stance performance builds, off-road trucks, and drag racing setups where maximum track width is desired.

Consequences of ET deviation

ET is not the same as backspacing, which is a measurement used primarily in the North American truck market. Backspacing measures the distance from the back edge of the rim to the mounting face. The conversion: ET = backspacing − (rim_width_inch × 12.7 + 11.25). Always encode ET in millimeters — it is the universal standard used by all wheel manufacturers globally.

TPMS: the fourth fitment dimension that aftermarket wheel listings ignore

TPMS (Tire Pressure Monitoring System) has been mandatory on all new US passenger vehicles since September 2007 (model year 2008). The law requires a warning when any tire pressure falls 25% below the recommended cold inflation pressure. Direct TPMS systems — the dominant design — place a pressure sensor and radio transmitter inside each wheel, mounted to the valve stem or banded to the drop center.

When buying aftermarket wheels, TPMS introduces four compatibility dimensions that almost no aftermarket wheel listing encodes:

1. Valve hole diameter

The standard valve hole in modern aftermarket wheels is 0.453 inches (11.5mm). This accommodates both snap-in rubber TPMS valve stems and metal clamp-in stems used by most OEM sensor designs. Honda uses a non-standard 0.625-inch (15.9mm) valve hole on many models — the Honda Accord, CR-V, Pilot, Ridgeline, and Odyssey among them. A Honda OEM TPMS sensor (which fits the 0.625-inch hole) will not fit an aftermarket wheel with a standard 0.453-inch hole. The buyer must purchase replacement sensors or have the wheels drilled to the correct size. An AI agent that doesn't flag this leaves buyers with a permanent TPMS fault after installation.

2. Sensor frequency

North American vehicles use 315 MHz for TPMS sensor communication. European-specification vehicles use 433 MHz. Most vehicles sold in the US — including European and Japanese brands — use 315 MHz. However, some European import variants (especially parallel imports or vehicles purchased abroad and registered in the US) may use 433 MHz. A sensor at the wrong frequency is never recognized by the vehicle ECU — the TPMS warning light stays on permanently. Encode wheel_tire.tpms_frequency_mhz for sensor compatibility filtering.

3. Sensor protocol

TPMS sensor manufacturers — Schrader, Pacific Industries (TRW), Continental, Hella — each use proprietary data protocols even at the same frequency. A Schrader sensor on a vehicle expecting a Continental protocol produces an unreadable signal. Programmable "universal" TPMS sensors (Autel MX-Sensor, Schrader EZ-Sensor, Dill Air Controls) solve this by encoding any OEM protocol during a TPMS relearn procedure, requiring a TPMS scan tool or visiting a dealer/tire shop.

4. Drop center clearance

Band-mount TPMS sensors attach to the wheel drop center with a stainless steel band. The drop center must have sufficient depth for the sensor body to clear the tire bead during mounting. Very low-profile wheels (particularly "lip" or "stepped" designs) may have insufficient drop center depth for certain sensor bodies. This is rarely disclosed in product listings and requires physical measurement to verify.

Complete JSON-LD and Liquid snippet for wheel fitment

JSON-LD for a specific aftermarket wheel

{
  "@context": "https://schema.org",
  "@type": "Product",
  "name": "Enkei RPF1 17×9 ET+45 Matte Black — 5×114.3 73mm",
  "description": "Enkei RPF1 single-piece cast/flow-formed alloy wheel. 17-inch diameter, 9-inch width, ET+45 offset, 5×114.3 bolt pattern, 73mm center bore (hub rings required for Toyota/Lexus 60.1mm hubs). 16.7 lb per wheel. Load rated to 1,565 lbs per wheel (710 kg). Fits: 2015–2023 Subaru WRX STI, 2018+ Toyota Camry, 2019+ Toyota Corolla (verify fitment by full vehicle spec).",
  "sku": "RPF1-17X9-ET45-5X114-MB",
  "brand": { "@type": "Brand", "name": "Enkei" },
  "additionalProperty": [
    { "@type": "PropertyValue", "name": "bolt_count", "value": "5" },
    { "@type": "PropertyValue", "name": "pcd_mm", "value": "114.3" },
    { "@type": "PropertyValue", "name": "bolt_pattern", "value": "5×114.3" },
    { "@type": "PropertyValue", "name": "center_bore_mm", "value": "73" },
    { "@type": "PropertyValue", "name": "hub_ring_required", "value": "true" },
    { "@type": "PropertyValue", "name": "hub_ring_sizes", "value": "73→60.1mm Toyota/Lexus, 73→56.1mm Honda, 73→66.6mm Mercedes" },
    { "@type": "PropertyValue", "name": "rim_diameter_inch", "value": "17" },
    { "@type": "PropertyValue", "name": "rim_width_inch", "value": "9" },
    { "@type": "PropertyValue", "name": "wheel_offset_et", "value": "45" },
    { "@type": "PropertyValue", "name": "wheel_weight_lb", "value": "16.7" },
    { "@type": "PropertyValue", "name": "load_capacity_kg", "value": "710" },
    { "@type": "PropertyValue", "name": "finish", "value": "matte-black" },
    { "@type": "PropertyValue", "name": "tpms_valve_hole_inch", "value": "0.453" },
    { "@type": "PropertyValue", "name": "fitment_type", "value": "universal" }
  ]
}

Shopify Liquid snippet — wheel_tire.* metafields

{% assign wt = product.metafields.wheel_tire %}

{% if wt.bolt_pattern.value %}
  <tr>
    <th>Bolt Pattern</th>
    <td>{{ wt.bolt_pattern.value }}
      {% if wt.pcd_mm.value %}
        ({{ wt.pcd_mm.value }}mm PCD)
      {% endif %}
    </td>
  </tr>
{% endif %}

{% if wt.center_bore_mm.value %}
  <tr>
    <th>Center Bore</th>
    <td>{{ wt.center_bore_mm.value }}mm
      {% if wt.hub_ring_required.value == "true" %}
        <span class="badge badge-warn">Hub rings required</span>
      {% endif %}
    </td>
  </tr>
{% endif %}

{% if wt.wheel_offset_et.value %}
  <tr>
    <th>Offset (ET)</th>
    <td>ET{{ wt.wheel_offset_et.value }}mm</td>
  </tr>
{% endif %}

{% if wt.rim_diameter_inch.value and wt.rim_width_inch.value %}
  <tr>
    <th>Rim Size</th>
    <td>{{ wt.rim_diameter_inch.value }}″
        × {{ wt.rim_width_inch.value }}″</td>
  </tr>
{% endif %}

{% if wt.tpms_valve_hole_inch.value %}
  <tr>
    <th>TPMS Valve Hole</th>
    <td>{{ wt.tpms_valve_hole_inch.value }}″
      {% if wt.tpms_valve_hole_inch.value == "0.625" %}
        <span class="badge badge-warn">Honda-specific — standard sensors do not fit</span>
      {% endif %}
    </td>
  </tr>
{% endif %}

{% if wt.hub_ring_sizes.value %}
  <tr>
    <th>Hub Ring Sizes</th>
    <td>{{ wt.hub_ring_sizes.value }}</td>
  </tr>
{% endif %}

Metafield reference table — wheel_tire.* namespace

5 AI agent wheel recommendation failures and how structured data prevents them