Ok I think I know about when you use Long Cages etc. I have a long cage RD that I've used on a 13-29 cassette. But I've also used this cassette on a medium cage. What I want to know is is there one cage I could use to run a 12-25 cassette and a 13-29?
I take it you are running Campag then? As I don't believe sh*ma*o produce rear cogs in that ratio. IIRC you can only run the 13 29 on a long cage, which will not work at the lower 12 25 ratio end, so I think you may have answered your own question. Depending on the terrain you ride in generally, a 13 29 is for BIG hills/Alpine climbs, run with a triple or compact chainset. 12 26 should get you up most hills comfortably in 39 52, or go for a 34 50 compact , if you have lots of steep climbs in your neck of the woods. Hope this has helped?
you can run any cage as long as its the right speed. long = some off road ? but mainly road mtb short = off road mtb short = road/ racing
If you are talking Campag then I can confirm that you can run a short-cage mech with both a 12-25 and a 13-29 cassette. I run these with a 34-48 Compact chainset which with a 14 tooth difference would mean you could also use a 39-53 chainset no problem. If a short-cage can cope with this then a medium or long would have no problem either.
It's for sportives, the White Rose Classic in particular. I'm a rubbish climber and need all the help I can get. I ran a 36/29 last year and even then I could have done with a lower gear.
When I enquired at one of my LBS about this dilemma, I currently run a short cage 11t-25t in conjunction with a compact 34t 50t chainset ( New UT centaur) I was told if I wanted to change to a 13t-29t I would have to swap my current RD for the long cage in order for it to index correctly, and this was after consulting the Campag website, as the guy in the shop wasn't sure himself, and neither was the chap who was with him. As I didn't have £171 on me to purchase a new long cage RD and a 13t-29t rear cog, I decided (on advice of the LBS guy) to try a bit harder on my climbing, I did and (it worked).
what ????????????????????????????????????????????? what you can change a long cage for a short as long as it ie the mech is the right speed. yes.................................. no.........................................
Forgive him, he banged his head recently. Its all about tooth 'difference', or in other words the ability of the spring-loaded cage plate to accommodate the cog and ring set up on the bike. The longer the cage the greater the capacity. Its really easy to work out coz its simple sums and takings away. eg my Mtn bike; 40t minus 30t chainrings = 10t difference. 32t minus 13t cassette sprockets = 19t difference. 10t + 19t = total tooth difference of 29. The only other consideration of note is the 'maximum sprocket' size, roadbike mechs have a lower max tooth capacity than mtn bikes. A roady mech wouldn't cope with my 32t largest sprocket. Whereas a mtn bike mech wouldn't follow the sprockets very closely on a road cassette. Max tooth difference and max sprocket size are written on the box and are listed in the installation instructions of every rear mech. Hope that makes sense.
Its not about indexing correctly its about the cage plates ability to accommodate the tooth difference. The 'indexing' wont be affected in any way. The rear derailleur does two jobs, it moves the chain between sprockets in response to instructions given to it via the shifters and it accommodates chain slack when changing between different sized sprockets. The toe-rags in your LBS do not know what they are talking about.
That's how I understand it too, but surely the larger and therefore the more teeth that the largest rear cog has, the longer the RD cage has to be, in order to accommodate the slack of the chain as it moves across the gears, therefore a short cage will hit the bottom of the largest cog, that's my understanding of why a 29t rear cog will need a long cage, or am I wrong? The Toe Rag is a kiwi, if that makes a difference? LOL!!!
