Comprising an axle, bearings and hub shell, a bike hub is the mechanism located in the middle of the bicycle wheel. A rear wheel hub is connected to the dropouts or rear chain, whilst a front wheel hub is connected to the forkends.
Typically there are three types of rear wheel hubs:
The freehub – this is where the bike cassette slides over the hub, which in turn works as a derailleur when it comes to changing the bike gears. This is the most common type of rear wheel hub
The threaded hub – this involves directly screwing the gear clusters and single costs onto the hub. This type of rear wheel hub is most commonly seen on older bikes and track bikes
The internal hub – these contain the gears within the actual rear hub. The hub outer turns at a different, but adjustable, speed to the sprocket. The internal hub gears are usually more reliable than external derailleurs given they are easier to keep clean, are weather-proof and don’t require as much maintenance (because they are protected from the natural elements when in use)
Although there are variations of up to 14 speeds, rear hub gears are most common in three to eight speeds.