# Chain Bouncing off



## skrap1r0n (Oct 15, 2010)

A few weeks ago, my gf and I purchased some Cannondale F8's. one thing we have noticed is that on particularly rough downhill runs and a drops of about 15" or so, We have had the chain jump off the chainring. 

As motorcyclist, we are familiar with chain stretch and adjusting it, however with a rear derailleur keeping tension, (as opposed to rear axle position on a motorcycle), I am wondering what we can do to fix this. Is there a way to adjust the tension the rear derailleur puts on the chain? Is there a technique to keep more tension on the chain when moving through particularly rough downhill areas?


----------



## JasonInBTR (Jul 19, 2010)

What gear combo are you in when the chain skips off? If you are close to a little-little combo there is alway going to be a good bit of slack in the chain. Have you checked that the chain length is proper? I would hope that the LBS would have done this when putting the bike together but it might be worth checking. If it is a SRAM chain you can just take the quick link out, dethread it from the rear derailleur and lace it over the big ring and big cog. There should only be about 2 links of slack in it. If there is considerably more this may be your problem. If it doesn't have a quick link you'll have to break the chain to measure this.

I would also check the high/low adjustment on the front derailleur.

Lot of good stuff here if you haven't found it already.

http://www.parktool.com/blog/repair-help

Jason


----------



## skrap1r0n (Oct 15, 2010)

They were new bikes, so I am assuming it is the correct length chain. As far as what gear we were in, its hard to say for sure, but I know we both ~usually~ keep it in the middle chain ring on the front. Where it is in the rear is anyones guess, lol.


----------



## nachomc (Apr 26, 2006)

Don't assume correct chain length, but I wouldn't start there either. Try to keep the chain in the large chain ring on the drops and extra rough stuff if you can. That should keep better tension and hopefully prevent the chain from flying off.


----------



## xenon (Apr 16, 2007)

You may need to adjust the front derailleur cable - likely, to increase the tension, so that the cage would be closer to the biggest ring. I don't think, High and Low limit screws adjustment will help, as they have nothing to do with position of the cage when the chain is in the middle ring.


----------



## mnigro (Jul 31, 2007)

sometimes there is nothing you can do to keep the chain from getting bounced off. If you move to a 2x9 you can see about fitting it with a chain guide/tensioner if the probelm persists. Can always shorten the chain a little too and just refrain from using certain gearing combos.


----------



## mfrench2013 (Jun 20, 2010)

get a chain guide. they sell ones for single or dual chain ring setups. look at mrp, e13, blackspire.


----------



## paco664 (Sep 18, 2010)

get a chain tender..... it is a little plastic ring you can put right on the inside of the little front ring and it has a little plastic arm that will keep the chain from popping off on the inside.... it costs about 6 to 10$......


----------



## djriddle (Oct 6, 2008)

In all my time in shops I never saw a new bike from a manufacturer with the wrong length chain. It could happen, but I doubt it is your problem. Gear choice (as already mentioned) can leave you with a slack rear derailer that is more likely to drop the chain. Also I would suspect the front derailer adjustments, but if it's happening on both bikes then it would be a strange conincedence unless both bikes were built by the same person and that person is doing something a bit off. Paco mentions a very good idea. I don't remember the manufacturer or the name even, but last time I looked in a QBP catalog they were still in there.


----------



## skrap1r0n (Oct 15, 2010)

we bought them new at the same LBS. After reading here, it is probably a combination of poor gear selection and front derailleur mis-alignment. To be clear, its not like they both pop off at the same time going down the same hill or drop. It has happened to me about 2 times, and I think hers has jumped a couple of times. If I had to guess, I would say its jumping once every 2 or 3 rides.

I know on mine, I have some issues selecting the ring I want on the front. I'll get it in to the LBS and have them take a look at it. We need a few cable tightened anyway and we are still within our "free maintenance" window from when we purchased the bikes.


----------



## bobby100 (Jun 21, 2010)

is it the rear. I had the same problem, I was running a deore rear deirellier, now a sram x0 now solid as a rock. cheaper derailier have more moving parts so they bounce around alot, sram makes ones with less moving parts and they well not move.


----------



## Varaxis (Mar 16, 2010)

I have the same problem with a SRAM XO front and rear with a 2x10. Chain keeps coming off the big ring. On a drop, it with a quick right turn after, it comes off onto the crank arm. Going straight on a fast descent with grapefruit sized rocks, it drops down to small ring. I haven't been able to keep the chain on, but I just get the chain back on by spinning the cranks forward and shifting to the small ring when I see the chain is about to get back onto the teeth. I haven't really had the chain get sucked down into the BB yet.


----------



## LyNx (Oct 26, 2004)

Well there's your problem, I have never gotten a bike pre-built that had the correct length chain, it always errs on the side o\f a noob throwing it into big -granny and not ripping ther rear derailleeur off because of bad gear combos. Put the bike in Big Ring and 3rd largest cog, if the rear dearailleur arm is not point either verticle (6 o'clock) or forwards towards say 5 o'clock, the cain is too long.

Another thing you can do on the downs to help stop chainslap and reduce the chance of the chain jumping off is to put it in the big ring and then one of the larger cogs. Also you need to check that the derailleurs limit screws are adjusted properly, you can also play a bit with the B-limit screw to help tension the rear dearilleur. Visit the Park Tools web site for very good, detailed instructions on anything bike related.



skrap1r0n said:


> They were new bikes, so I am assuming it is the correct length chain. As far as what gear we were in, its hard to say for sure, but I know we both ~usually~ keep it in the middle chain ring on the front. Where it is in the rear is anyones guess, lol.


----------



## Mount Dora Cycles (May 29, 2009)

bobby100 said:


> is it the rear. I had the same problem, I was running a deore rear deirellier, now a sram x0 now solid as a rock. cheaper derailier have more moving parts so they bounce around alot, sram makes ones with less moving parts and they well not move.


This made me laugh so hard. I love this forum.


----------



## alshead (Oct 2, 2007)

@varaxis- I'm having the exact same issue you described. Did you ever have any resolution?


----------

