What kind of derailleur should you use on an all-mountain MTB? Short, Medium or Long cage? and why?

Question

What kind of derailleur should you use on an all-mountain MTB? Short, Medium or Long cage? and why?

Answer 1

The cage length needed is determined by the range of gears to be accommodated. Basically, a wider range of gears requires more accommodation in the derailleur to keep the chain reasonably tensioned across the full range of cogs. The specs for the derailleur will list what freewheel cog ranges will be accomodated.

A triple fron chainring (as is standard on a mtb) requires more acommodation than a double ring setup as on many road bikes.

So, basically, a mountain bike will almost always require a medium or long derailleur (usually long) cage, while a road bike will usually require a short or medium.

Answer 2

They say if you dont know what kind of derailleur to buy,  then buy a long cage.  The difference is the long cage takes up the most cable slack and the short cage takes up the least.  But the short offers the quickest and most precise gear change then the long cage.  The middle cage is exactly that a middle ground between the two.  I would recommend the long gear on a all mountain bike though.