>>1712385It's a bike with an internal gear hub (IGH) built into the rear wheel, which is used instead of a derailleur to shift gears, and uses a belt instead of a chain. Theoretical benefit is that the IGH doesn't get out of whack as easily as a derailleur setup because it's not as exposed to the elements or things bashing against the gear changing mechanism, and the belt doesn't stretch like a chain does and lasts longer. You can also shift while stopped, which is a nice feature.
Quality is all over the place. Shimano and Sunrace/Sturmey make their shit to a low price point for OEMs, and since IGHs are somewhat complex like motorcycle or automotive transmissions, but much lighter and smaller, they have to cut a lot of corners in manufacturing to meet those price points. Rohloff and Pinion are much higher quality but much more expensive. Pinion requires the whole bike to be built around its gearbox, but one benefit of it is that it puts the gearbox's weight in the best place. Shimano's Alfine 8 is pretty reliable but the shifting always feels sloppy.
IGHs are more of a pain and more expensive to fix when they go wrong, often requiring replacement if it isn't a simple matter of tensioning the cable right. They're also heavy, you lose a ton of efficiency, and in most cases only work with twist shifters. The best application for them is e-bike, although a lot of ultra-hardcore touring bike riders and people who build apocalypse bikes love Rohloff. MTBers who deal with a lot of mud and crud like 'em too. They usually last forever so long as you change the oil every 5000km. The only failures I know about are a few hub flanges that cracked over 10 years ago, and Rohloff was good about replacing them. Then they revised the design so it wouldn't happen again.
