Joined: Jan 2010
Posts: 9,835
Likes: 1,816
From: Northern California
Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.
The short cage on a mtb derailer is longer than on a similar road derailer. I've swapped them and the difference was there.
They are intended for use with triples, just not combined with the x-32t cassette in most cases.
Road Fan is dead-on, the derailer's capacity and largest cog size defines what it can handle. Shimano derailers having two sprung pivots (unlike SRAM's) will handle considerably-larger than recommended largest cogs, but at some cost to shift quality going up to the largest cogs due to the fast-closing chain gap. So those shifts may have more of a jank to them.