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There are two types of hubs, open-bearing and cartridges. The cones and bearings of open-bearing hubs must be adjusted to let the hub spin freely, with little play. The bearings in both types of hubs need regular checking and lubricating.
How Hubs Work
The hub allows the wheel to revolve. Quick-release mechanisms or nuts secure the axle into the bike’s frame. The axle remains static while the hub body spins around on bearings. Spokes run from the hub’s flanges to the rim of the wheel -- as the hub spins, so does the rim.
The drivetrain transfers the rider’s power from the pedals to the rear wheel, while the front wheel is essentially pushed along by the revolutions of the rear. The gears on a bike are located on the rear hub, either as a hub-gear unit or as multiple cogs in the case of derailleur gears.
The freewheel mechanism, which is also on the rear hub, allows a rider to stop pedaling while the bike is in motion -- for example, on a downhill stretch of road. This mechanism is part of the hub in both hub gears and hubs with cassette cogs.
Free-spinning hubs are an essential part of an efficient bike. Their bearings must create as little friction as possible, so as not to slow the cyclist’s forward progress.
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Right: Exploded view of a Cartridge
Right: Components of an Open-Bearing Front Hub
The body on an open-bearing front hub spins on ball bearings that are set within, and at each end of, the hub body. Each set of bearings is held in place by a cone (not visible) that is screwed down on the thread at the end of the axle. A locknut (not visible) locks the cone in place on the same thread. If the hub is held by a quick-release mechanism, the axle is hollow to allow the quick- release skewer to go through it.
Axle: Remains static as the wheel revolves; Hub body: Rotates around the axle; Ball bearings: Support the hub body; Quick-release skewer: Locks the axle.
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