Editing Inline skates (section)

=== Bearing misalignment ===

When skaters customize their setups or rotate wheels, careful attention must be paid to how bearings are re-installed. If bearings are not properly aligned, or if they are allowed to shift after installation, the wheels can tilt. Misaligned wheels roll unevenly, drag against the frame, generate vibrations, and overheat the polyurethane tires, hubs, and bearing assembly. This not only reduces performance but can also cause tires to debond from their hubs and lead to premature wear on bearings and axles. '''Bearing misalignment''' is one of the most harmful issues in skating, second only to bearing contamination from dirt.<ref name="usenet-chen-FAQ-inline-wheels"/><ref name="hirschmugl-august-skate-wheel-plastic-hub-patent-1954"/><ref name="brennan-olson-1987-patent-modern-inline-skates"/><ref name="peterverdone-bearings-and-lubrication">{{cite web
|url=https://www.peterverdone.com/archive/skatebearings.htm
|title=Bearings & Lubrication
|first1=Peter
|last1=Verdone
|date=2012
|website=PVD Designs
|url-status=live
|archive-url=https://web.archive.org/web/20120215062022/http://www.peterverdone.com/archive/skatebearings.htm
|archive-date=2012-02-15
|access-date=2025-05-31
}}</ref><ref name="powell-svensson-inline-skating"/>{{rp|39–45}}

In the 1980s, Rollerblade and Kryptonics jointly developed plastic hubs for inline skate wheels. A key design objective was to create precise, rigid '''bearing seats''' within the hub to hold and align the bearings accurately. Each bearing seat is formed on the side of the hub as a '''bearing recess''' measuring 7mm deep, the exact width of an ISO 608 ball bearing, allowing the bearings to be press-fit with a flush mount.<ref name="brennan-olson-1987-patent-modern-inline-skates"/><ref name="cryptonics-1995-patent-bearing-seat-to-eliminate-bearing-clicks"/><ref name="hook-1995-patent-two-piece-wheel-hubs"/><ref name="powerslide-download-guides-bearings-by-wicked"/>

Inline skate wheel hubs have a standardized width of 24mm, and all inline frames are designed to accommodate hubs of this exact size. With bearings mounted flush on either side, this leaves a 10mm gap between them. This gap is filled by a '''bearing abutment''', an internal protrusion molded into the hub that acts as a mechanical shoulder to precisely position and support the bearings.<ref name="le-roller-en-ligne-on-physics-of-inline-skate-wheel"/><ref name="brennan-olson-1987-patent-modern-inline-skates"/>

A ball bearing consists of two concentric races that rotate relative to each other. The '''outer race''' is friction-mounted into the bearing seat, becoming fixed in place with the hub and, by extension, the polyurethane tire. As a result, it rotates together with the wheel.<ref name="cryptonics-1995-patent-bearing-seat-to-eliminate-bearing-clicks"/>

The '''inner race''', by contrast, is held stationary as part of the axle assembly. A '''spacer''' matching the 10mm length of the hub’s bearing abutment is placed between the two inner races. When the axle bolt is tightened, it clamps the frame walls around the bearing assembly, which includes the two inner races and the spacer. This creates a rigid structure that binds the axle, spacer, and inner races together as a single fixture attached to the frame and, ultimately, the boot.<ref name="brennan-olson-1987-patent-modern-inline-skates"/><ref name="cryptonics-1995-patent-bearing-seat-to-eliminate-bearing-clicks"/><ref name="joyner-inline-hockey-1995"/>{{rp|19–24}}<ref name="miller-get-rolling-2003"/>{{rp|43–44}}