Registered: Nov 2003
Location: Detroit suburbs
Re: how much is too much chain?
Originally posted by kmay
I have a similar set-up as yours...24, 44, 54 on an 8 speed, t-cycle idler and 11 - 34 mega range cassette with shimano XT long cage derailer (thanks to Sheldon Brown for pushing this spelling).
When I first got the bike, I rode it some and then examined and fine tuned the components.
On my work stand, the chain drags the front derailer cage as there appeared to be "too much slack" when on the 24 T. The chain pooled over the bottom of the cage and looked impossible to ride. Since I never heard this chain scrape before, I looked a little harder.
I discovered the top or power side of the chain is under tension when under any load, therefore the chain will not drag the cage as long as I am pedaling. If you based your excessive chain length diagnosis from chain dragging under no load on the work stand, you may not have a problem. Next time you have the bike on the stand, squeeze the rear brake a bit while pedaling to see the chain line under load.
The b-limit screw is supposed to keep the derailer jockey from hitting the cassette under light loads and slack chain when you are in the 34 tooth rear or largest diameter gear. This adjustment will help in the small - big combo but is of no help once you get out there on the 11 tooth. However, you have the derailer cage spring to tension the chain and is should be enough to keep the bits apart.
I have enough chain to use the big - big combo and have no problems that I can attribute to too much chain. On the small - small combo, I do not hear any chain rub from either the return chain hitting the jockey or dragging on front derailer cage, as long as I am pedaling under a load.
I think I am in basic agreement.
When in the small/small combination the top of my chain will drag on the bottom of the front derailleur cage also. However, with any load on the pedals at all, it lifts off and there is no problem.
I just chalk it up to one of the necessities of life when you have such wide gearing.
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