These derailleurs, introduced in 2004 in the XT and XTR groups maintain position over the largest sprocket on the cassette when no cable tension is applied.

Some cassette systems from the late 1980s and early 1990s use a threaded small sprocket to hold on the larger splined sprockets, the entire set referred to as a cluster.

When the transmission turns the smaller front sprocket, power is transmitted along the chain to the larger rear sprocket, which then turns the rear wheel.

Features include a taller seat height, higher ground clearance, larger wheelbase, increased tire size, longer swing arm and larger rear sprocket for better acceleration with a heavier rider.

Lower speeds for hill use was by addition of a larger rear sprocket overlaying the usual one, a process which could be performed without removing the rear wheel.

It only geared up, so a relatively large rear sprocket was necessary to give a reasonable development when combined with a normal front sprocket.

In derailleur mechanisms the highest efficiency is achieved by the larger sprockets.

Low normal or rapid rise rear derailleurs return the chain to the largest sprocket on the cassette when no cable tension is applied.

A larger sprocket will give a more efficient drive, reducing the movement angle of the links.

For example, gashers are used for the production of large roller-chain sprockets.