Rear derailleurs are problematic, particularly on mountain bikes. They get bent, they get gunked up, and they’re exposed to the elements. While sealed hub transmissions lack these problems, not all of them have axles that are strong enough for multi-terrain use, they add revolving weight, and that weight is added in the back of the bike – not low and in the middle, where you want it. German company Pinion has developed what it claims is something better ... a sealed gearbox located adjacent to the bottom bracket.
Read the full article: Pinion sealed gearbox offers an alternative to those darn derailleurs