Much as mountain bike technology has advanced since the days of friction shifting and elastomer shocks, most MTBs are still equipped with dangling, fragile rear derailleurs and dirty chains. Switching to a belt drive or a hub transmission are a couple of options, but Polish mountain biking medalist Gregory Zielinski has created another. His Nuseti bike features what he calls the Inner Drive System (IDS) – a 16-speed planetary gearbox that's incorporated into the bottom bracket, and a chain that's enclosed within the frame.

Both the gearbox and the chain are sealed against water and outside contaminants, plus they're kept lubricated by separate sealed-in oil baths. This means that riders won't be exposed to greasy crud, and won't need to frequently clean or lube the drivetrain.

The gearbox can withstand up to 184 lb ft (250 Nm) of torque, which means that a force of 326 lb (147 kg) can safely be applied to each pedal. Although it has less individual gears than a regular setup, it has a gear range of 570 percent, which is in the neighborhood of that offered by a traditional mountain bike with a three-chainring configuration.

Also, as with other planetary gearboxes, it allows the rider to change gears even when they're not pedaling, or while the drivetrain is under a heavy pedaling load. Additionally, like the Pinion gearbox but unlike hub transmissions, its location keeps the weight both low and central.

It will be offered in four frame sizes and three wheel sizes (26, 27.5 and 29 inches)

Gear shifts are initiated using two handlebar-mounted trigger shifters, with the left one being used to go into higher gears, and the right one used for down-shifting.

The chain consistently runs in a straight line from the gearbox to the rear hub, so riders don't need to worry about mechanically straining it by placing it at too much of an angle. Additionally, it isn't used in the gear-changing process, which is managed purely by the workings of the gearbox. For these reasons, Zielinski claims that it's virtually impossible to break the chain.

Some people might wonder why he didn't just go with a belt drive, but Gregory tells us that the one-piece construction of a belt doesn't allow it to be installed within the IDS, plus he maintains that chains are "a more efficient and solid solution."

At the moment, though, he's focusing on raising funds via Kickstarter. Assuming the funding goal is met and the bike goes into production, a pledge of US$3,415 will get you an IDS-equipped Nuseti frame, with $6,262 required for a complete bike. The estimated weight of the final production model is 23.6 lb (10.7 kg), and it will be offered in four frame sizes and three wheel sizes (26, 27.5 and 29 inches). Zielinski also plans to produce a full-suspension model.

Source: Kickstarter