keepin' it rural
ok...is this a true statement?
if your front derailleur is set up up and adjusted correctly then you shouldnt be-able to drop your chain on to the bottom bracket.
i was talking with my LBS about putting on a AJ's chain guide, and he said that it was just a band-aid fix for the problem and if it was set-up right that i shouldnt be dropping the chain. which i don't normally drop my chain, but every once in a while when going through a rough section and im in to low a gear combo it will flop off onto the BB and scratch the sh*t out of my shell and pivot. im running a standard 3x9 set up and it is adjusted properly (i think) because it never shifts into the BB it only happens when it get flopped off from a rough section...am i not setting something up correctly or would the AJ's be a good solution?
You should not be able to shift your chain to the bottom bracket nor should it fall off the chainring.
It might be a dragging freehub (causes the chain to be loose on the top).
Is the chain tensioned properly by the RD.
Are you changing the FD and the RD at the same time?
keepin' it rural
Originally Posted by jeffscott
it cant shift into the BB because the limit screw is keeping it from going that far so im pretty sure thats set up right.
and im not shifting the FD and RD at same time.
not sure about the freehub, how can i check that?
and the RD seems to tension properly.
the only time i've dropped it is when going down a rocky section and it got bounced off, should it not be able to be bounced off no matter how rough?
thanks for your input...
a little sideways answer: Lenerd Zinns column over at VeloNews has mentioned a few times devices like the Deda dog fang - which I believe is similar to the gizmo you are talking about. He's shown pictures of them on [roadie] pro bikes. These are built and maintained by the best mechanics in the world - not by a nose picker HS dropout like the ones that wrench at your LBS probably.
IOW better mechanics than the ones that told you that disagree that a jump stop gizmo is just a bandaid.
better yet, make a bet with the guy: have him adjust your derailleur so it shifts reliably but the chain never drops, with the stipulation that if he's unable to do it he buys you the jump stop you wanted in the first place.
Pedal the drive train with the rear wheel on, up on the stand.
Release the pedals.
Do the cranks continue to rotate (driven by the rear wheel).
This would indicate more drag than normal in the freehub.
I lose my chain off the inner ring occasionally, but usually due to shifting under power, or some other bonehead move on my part.
I can't remeber my chain ever falling off over a rock garden. I ride the Eastern slopes so we have a few of those.
Sorry I can't help more.
I hear this every once in a while from armchair mechanics, it's fun for some people to criticize other people's wrenching abilities using absolute statements like this with no merit. I know, I've worked with mechanics like this, and they're rarely good at working on bikes and incredibly unhelpful.
Originally Posted by summud
On paper, sure a properly setup front derailleur will never drop the chain....in a repair stand. I would say a bike that has brand new suspension pivots with zero play, near perfect chainline, long chainstays, Shimano chainrings and a high-end front derailleur (XTR, XT, etc.) with zero play in the parallelogram pivots will very seldomly drop a chain. I think a lot of the arrogant-type mechanics fail to realize the number of factors than ensure good derailleur shifting, and that not all can be controlled or "fixed".
Some bikes I've encountered simply just drop chains because of a combination of short chainstays, low-quality chainrings, a cheap front derailleur and possibly poor chainline. Specialized was for a while (and might still be) specing some of their road bikes w/ triples with a cheap knockoff of the Deda Dog Fang because the chain would tend to drop if simultaneously shifting larger cogs in the back and into the smallest chainring. No amount of derailleur adjustment could prevent this, unless shift performance into the small ring was compromised. And this is a road bike; not gonna see any huge drops or bumpy trails.
The right amount of outside variables will make a chain drop on any bike with a triple. That's why chain guides exist for downhill racers and freeriders. A bike is particularly suceptable to dropping a chain if shifting into the small chainring whilst in a smaller cog, because the chain tension is at it's lowest. I would double check the adjustment (make sure the outside plate of the derailleur is in line with the chainrings and at the right height) and check the chainrings for any bends or damage. A Dog Fang or something similar might alleviate the problem a little, but a little change in technique when riding through rough sections may work better. Riding downhill sections in the big ring and a middle cog gives the chain more tension then in the middle ring with a smaller cog and similar ratio. Shifting front and rear at the same time increases the likelihood of losing the chain as well, as does dumping the chain into the small ring while in the largest rear cog while going over a rough section of trail (somewhat low tension combined with cross-chaining; the chain is at a more extreme angle in relation to the chainrings and might not catch on any of the teeth on the small chainring, short chainstays increase this angle).
I'm not trying to stir up an argument, arrogant mechanics just annoy me. :
Unemployed Mech is spot-on, many inexperienced mechanics will spout this sort of knowledge for a while. They are right about 80% of the time, but when you get down to it, there are a lot of suspension bikes that just don't shift properly up front. What Joe Wrench learned in the Shimano Clinic doesn't necessarily translate to the real world.
That said, you say you dropped your chain in a rocky section of trail... sometimes this just happens, even if a bike is not prone to such things. Once or twice is annoying, more than that and you need to consider another solution. If you mainly ride XC, then a third-eye or dog fang might be just the ticket.
If you ride a lot of technical terrain, consider ditching your big ring and purchasing a chainguide. The e-13 DRS does a great job, but only works with the two inner chainrings.
keepin' it rural
thanks for the input...i think like JMH said i thinks its more of the annoyance thing than a adjustment thing, because im pretty anal about keeping my bike in order. but the two times that i have dropped the chain the were pretty nasty, twisting the chain up and really gouging my BB shell and pivot. so i really want to keep it from happening so i dont keep damaging my frame. with this being said i do ride alot of rocky aggressive trails (bootleg canyon, nevada) so im sure the issue will come up again, so what are the pros and cons of running just some sort of guard device or an full on bash guard and tensioner? thanks
My short response is: GET the AJ's Frameguard (chain guide)! These really work -- much better in my experience than the "fang" type guides. The can be used on frames where the fangs don't fit, and they are a MUCH more robust system for keeping the chain from dropping. If the chain moves too far to the left, it simply hits the beveled frameguard and slides right back down onto the chainring. When I started using one of these, my occasional chain drop problems vanished permanently. I haven't had a single drop in over a year since I started using one. The only thing to consider is the fact that it cannot fit every frame. I can fit most of them, however.
Originally Posted by summud
My longer response: I don't mean to sound too critical of your LBS, but I find their statement to be pretty ridiculous. Sure, a properly set up drivetrain will have fewer problems in this regard, but it's a mountain bike -- it bounces around. A chain/gear system simply isn't robust enough to guarantee that the chain will never drop to the inside -- it's just something that "can" happen once in a while, especially on more aggressive terrain. Just because one bike and/or rider has never encountered this does NOT mean that it "can't" happen. Just because you've never had a flat on a certain trail doens't mean that you "can't" get a flat on that trail. If a properly adjusted derailleur prevented chain drops, than (as somebody else already pointed out) why do downhill bikes have chain guides (often heavy duty ones that create drag) as a standard accessory?
The AJ's Frameguard is not a "band-aid" -- it's a "FIX." Properly set up (with the right spacers such that it forces the chain to re-engage the chainring), it literally prevents this issue from happening. That aside, ask yourself this: Even if a "properly set up" derailleur DID prevent this issue (which, once again, it does NOT), wouldn't you rather have the Frameguard just in case the system was slightly out of adjustment? Wouldn't you rather COMPLETELY avoid even the potential for this issue to occur? I know I would, which is why I plan to put one of these on the next bike I get right off the bat.
Last edited by lalittle; 04-12-2007 at 02:44 PM.
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