Advantages
- Hub gears are sealed within the hub, which protects them from water, grit, and impacts. Thus hub gears usually require less maintenance and can be more reliable over time than comparable external derailleur gear systems, which may require more adjustments and replacement of parts (front chainrings, rear sprockets, narrow derailleur-chain).
- Hub gears completely avoid the danger of collision with the spokes and wheel-collapse that derailleur systems can suffer.
- Hub gears can change gear ratios when the rear wheel is not rotating. This can be useful for commuter cycling with frequent stops and for mountain biking in rough terrain.
- Hub gears can be simpler to use for inexperienced riders, because there is generally only a single shifter to operate and there are no overlapping gear ratios. By contrast, modern derailleur systems often have two shifters, and require some forethought to avoid problematic gear combinations.
- Hub gears provide a means for shifting gear ratios on drivetrains incompatible with external deraileurs such as belt drives and shaft drives.
- The single chainline allows for a full chain enclosure chain guard, so the chain can be protected from water and grit and clothing can be protected from contact with the lubricated chain.
- The single chainline does not require the chain to bend or twist. As a result, the chain can be constructed differently, with parallel pins instead of barrel-shaped ones. Line-contact between the bearing surfaces, instead the point-contact of a derailleur chain, greatly extends the working life of all components.
- On bicycles with fixed chain-lines, no chain tensioner is required, eliminating a part that could otherwise become damaged in rough terrain- an advantage for off-road cyclists. Where a tensioner is required, a short cage is usually sufficient to take up the chain slack.
- The single external sprocket means that the wheel can have a hub with more distance between its flanges and be built with no or much less dish, making it laterally stronger than a similar wheel with narrower flange spacing and more dish to accommodate multiple sprockets. The hub shell of gear hubs is also often of a larger diameter than that of derailleur hubs, meaning the spokes on such wheels may be shorter.
Read more about this topic: Hub Gear
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