Quote Originally Posted by Marshy View Post
It's actually that you can slide the whole gearbox unit out of the engine case (like a cassette going in and out of a cassette player!) without having to drop the engine out and split the casing etc to get to the gearbox. Muuuuuch quicker and easier, and you can (in the rarefied world of top-level superbike/GP racing) do it trackside between sessions, to change internal gear ratios.

In the Aprilia's case, clearly it is not there for Max Falloffi.... errr... Biaggi and co to change internal ratios, but rather to quickly fix all their gearboxes that break every 5 minutes......
So those guys tweak the internal gearing ratios instead of or in conjunction with front / rear sprockets? If the latter, does it just allows finer adjustment for a particular track?