The bearings are what let the wheel spin with minimal resistance. Two designs dominate the market: loose-ball bearings (a cup-and-cone system with individual balls set in grease) and sealed cartridge bearings (a pre-assembled, sealed unit pressed into the hub shell).

• Sealed cartridge bearings generally run smoother out of the box and are simpler to service — swap the whole cartridge rather than repack loose balls.
• Loose-ball systems can be tuned very precisely by an experienced mechanic and are often easier to rebuild in the field with basic tools.
• Ceramic hybrid bearings (steel races with ceramic balls) reduce rolling friction versus all-steel bearings, though the real-world speed benefit is small and matters most at high, sustained loads.
• Bearing preload and race finish quality affect rolling smoothness more than material choice alone — a well-adjusted steel bearing will often outperform a poorly adjusted ceramic one.

The freehub is the mechanism that lets the wheel coast while you stop pedaling, then locks the wheel to the cassette the instant you push forward again. The gap between "you push the pedal" and "the wheel responds" is the engagement angle, and it's determined by how the freehub's pawls (or ratchet teeth) are arranged — a topic covered in detail in H-Works' ratchet vs. pawl mechanism guide.

Faster engagement mainly matters in situations where you need power immediately — technical climbing, track starts, or picking your way through obstacles — rather than steady-state riding, where engagement speed has little effect.

The hub flanges are where spokes attach, and their diameter, spacing, and drilling pattern determine how the wheel handles side loads (cornering, sprinting out of the saddle) versus radial loads (just supporting weight). Wikipedia's overview of the bicycle wheel is a useful primer on how hub, spokes, and rim work together structurally.

• Wider flange spacing generally improves lateral stiffness, which is why rear hubs are often built asymmetrically to compensate for the dish caused by the cassette.
• Even, correct spoke tension across a wheel matters more for durability and ride quality than the exact tension figures used — a wheel built to a tension appropriate for its rim and consistent across all spokes will hold true longer than one built to a "high" but uneven tension.
• Straight-pull spokes (versus J-bend) change how load transfers into the flange, which some manufacturers use to justify claims of added stiffness — actual performance varies by build quality more than by attachment style alone.

Hub bearings generate heat under sustained hard efforts, and grease selection affects how the hub performs as it warms up.

• Greases are rated for a temperature and load range; using a grease outside its rated range can cause it to thin out and lose protective film thickness, increasing wear.
• Sealed units trade a small amount of added friction (from the seal itself) for much better long-term protection against water and grit — usually a worthwhile trade for most riding conditions.
• Axle and hub shell materials with higher thermal conductivity (aluminum versus steel, for example) dissipate heat faster, which mainly matters for very long descents with heavy braking or extended high-power efforts, less so for everyday riding.

No single hub design wins on every axis — lighter, faster-engaging, more efficient designs generally cost more and may need more frequent service, while simpler, heavier designs tend to be cheaper to maintain and more forgiving of neglect.

Note: manufacturer efficiency and friction figures vary widely by test method and load conditions, and aren't standardized across brands — treat specific percentage claims from any single source with caution and compare like-for-like where possible.