Just out of curiosity what are the main factors that determine whether a long cage or short cage derailleur is fitted. The reason for the question is that both my bikes have 14/28 rear clusters but the one with the short cage Huret has 54/42 chainrings and the one with the long cage Suntour has 50/36 chainrings. It almost feels that they should be the other way round. Hope this is not a silly question!
Long cage v short cage derailleur
- Thread starter Nifty850
- Start date
Old Ned
Old School Grand Master
My experience is that short (or even Medium) cage mechs are fine for double chainsets but if you fit a triple - especially with a large rear sprocket - then a long cage may be necessary. I raced MTB's BITD with triple c/s and a short cage XT mech and 28 rear and it worked OK.
Or was it a Medium cage?............
Or was it a Medium cage?............
Jonny69
Senior Retro Guru
One factor is the largest size cog it can accommodate at the back, but it's a total capacity thing from highest gear to lowest gear including the front rings. The longer cage allows you to use a bigger range. On your 52/42 it's a 10 tooth difference whereas on the 50/36 it's 14. Presumably Suntour decided their shorter cage wouldn't have enough swing to take up a 14-28 block with a 14 tooth difference up front.
Short cage mechs tend to have less chain slap and so are preferable IF gear ratios allow. I.e. as Jonny says above, you need to consider the largest sprocket (can the mech climb the chain up there without hitting it?) AND total capacity (can the mech take up the difference if free chain length when the chain is on smallest chain ring/sprocket vs largest chain ring/sprocket).
In the olden days, the advice was to avoid running the chain at the extremes (the deflection tended to wear out chains quickly) but the principle remains the same.
Obviously, having a huge chainring, small sprocket and short cage mech also makes you more attractive to your preferred gender choice too.
In the olden days, the advice was to avoid running the chain at the extremes (the deflection tended to wear out chains quickly) but the principle remains the same.
Obviously, having a huge chainring, small sprocket and short cage mech also makes you more attractive to your preferred gender choice too.
There are two factors:
1 Road geometry mechs can have a different parallelogram slant and therefore not track the cassette shape correctly. Hence the need for a mech dropper for larger cassettes with some road mechs.
2 The cage length determines the amount of slack the mech can take up.
Whatever you do, make sure your mech can run big-big. It might not be something you would select deliberately, but Sod's Law means that one day you will. If unlucky, the bike solves the unsolvable by stuffing the mech through the rear wheel.
1 Road geometry mechs can have a different parallelogram slant and therefore not track the cassette shape correctly. Hence the need for a mech dropper for larger cassettes with some road mechs.
2 The cage length determines the amount of slack the mech can take up.
Whatever you do, make sure your mech can run big-big. It might not be something you would select deliberately, but Sod's Law means that one day you will. If unlucky, the bike solves the unsolvable by stuffing the mech through the rear wheel.
I recall riding back on that busy road up from Dover, having watched the tour around Dunkirk. A mate went for big-big but didn't have a long enough chain and his rear mech literally exploded into dozens of pieces. That was the end of the Dura ace 7200 derailleur I had given him. We fixed him up single gear, but Kent is far hillier than we anticipated and at the end of the day he was totally cookedhamster":155qoo3j said:
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