[Closed] Chain device for pressfit BB - No ISCG mounts????????????

Is a seat tube clamp mounted one an option at all?

Superstar do a seat tube mounted top guide but I think you're bolloxed for a bottom roller without going into 'bodge county'!

2011 Stumpy FSR so no seat tube and direct mount front mech. It's a bottom roller I want, the front mech sorts the top out OK. I pretty much thought I might have to move in to bodge county.

I had wondered about the SS one and machine out the inner to 42 MM

Could you go with a Chainstay mounted roller or Jockey wheel?

Spesh have started doing this on some of their 2012 models apparently, it's basically a DCD by another name...

Depending on your cable routing, Bionicon do a chainstay mounted one too.

http://www.bionicon.com/ac/c-guide-v02

Specialized have there own chain stay mounted one coming out next year [img] [/img]

This is the beauty of all these new standards coming down from road bikes which aren't needed!!

And I've just seen on the Spesh website that the 2012 bikes have ISCG05!!!

Sorry to ask what may be a dumb question, but what's the purpose of a lower chain device on a twin chainring setup, like the picture above?

It helps keep the chain on.

So if the chain on my 2x9 setup doesn't come off - there's no advantage in having one?

No.

Great - crosses chain device off the CRC wishlist...

It only adds weight and they can be noisey. If your front mech is setup nicely and your chain short enough, you should be ok.

When does the chain fall off? When changing down to the granny, or just when going down a teeth rattling descent? I used to have the chain overshoot the granny as I changed down occasionally, but replaced my triple FD with a double specific one and haven't had it happen since.

When it gets bumpy and you're trying to pedal over bumps or back pedal (mainly when dhing) The chain missing the granny gear would just be a badly setup front mech I guess.

I could see that backpeddaling would do it when the chain is flapping all over the place on a bumpy descent - but why would you do that?

I was in a Spec. Concept Store the other week and 'the Dangler' came up. Apparently they're not even designed to fit this year's models. The mechanic reckoned it could be easily modified from what he'd seen though.

When does the chain fall off? when going down a teeth rattling descent?

I run 2x9 & have shortened the chain, but found when I was quickly descending rocky trails in the 11t cog at the rear, the chain would sometimes jump from middle to granny. Chain devices really don't weigh that much & it has the added advantage of stopping the noise from chainslap.

Out of interest, would the extra tension in the chain help reduce the prospect of chainsuck?

I recently ditched the lower roller from my 2x8 HT, kept the chain sensibly short and retained the bash ring, thus far no real changes the chain stays on just fine, the next step however is probably to remove the bash as well I think, this will introduce a greater the risk of the chain heading off the top of the ring more than the bottom but the weight saving is not insignificant so it's probably worth trying it....

I think if I was going to a 1xN setup I'd probably want the security of a both a top and bottom retainer of some sort, but for a 2xN setup I don't think it's actually as critical, a suitably sized bash ring seems to help stop the chain riding off the top (But obviously adds some mass) and having the chain bounce on to the granny isn't as much of a problem as having it bounce off all together...

As for simply Not Back-pedaling, in my view you should be able to do it, it's not "incorrect technique" its setting your pedals for whatever corner/obstical you are approaching, can't see why anyone would accept not being able to back pedal other than if they were on a fixie...

I have created mine out of a hoseclip and a beehive one:

[img] [/img]

[img] [/img]

Not the best picture but basically I got a timber bracket (1mm thin bit of aluminium with two holes on each end) and bent that so it was a bit like a trapezium. Then slotted this between the hose clip (which has rubber so as not to damage the frame). Then I tigtened the hose clip. I then put a long bolt through the existing chain device (originally a BB mounted one) and a few bolts, fixed it all together.

It stays in place nicely but has good flex so it keeps the chain on but will happily flex and move to adjust to the chain movement which is great.