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Discussion Starter · #1 ·
So I was checking out my father-in-law's new CAAD12 and I saw a loose plastic tube around the front derailleur cable in between the frame and the clamp down spot on the derailleur.

I thought it was a plastic guide meant to prevent friction as the cable bends around the BB (as I'm used to on some other frames) and that the mechanic who did the build must have done a shoddy job.

However, later the same day at a local Cannondale dealer I saw the same tube on a dozen other builds and it was also always loose.

So is it supposed to be loose, or is it supposed to bent around the BB? And if it's supposed to be loose, what the heck is it for?
 

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what the heck is it for?
Possibly to keep the cable from being frayed when it contacts the front derailleur mechanism. Over the years, I've seen quite a number of bikes on which the cable touches the hinge or the spring of the front derailleur after the shift to the small ring. Never seemed to affect function of the derailleur or the life of the cable, though.

Shift your father-in-laws bike and see where the cable lands. I haven't got a CAAD12 handy right now to confirm or reject my guess.
 

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Discussion Starter · #3 ·
Good guess, but does not appear to be the case. I'm still thinking it's friction prevention for the bend but hope somebody can either confirm or explain. Maybe it's just to keep grime off the cable...
 

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I'm still thinking it's friction prevention for the bend but hope somebody can either confirm or explain.
Possible, but then why do all of them extend so far up? In some Cannondale bean counter's book, that would be a huge waste of plastic tubing.

Can't go with the grime guard notion. If the tubing is loose, grime will get in but can't get out readily. Worse than nothing at all.

Edit: found a photo. Is it possible that the tubing protects the cable from the sharp edges of the inboard derailleur cage plate with the cage in the small ring position? If that's the answer, then there are some awfully tight clearances down there.
 

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Neophyte
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Discussion Starter · #5 ·
Thanks for posting picture, sorry I neglected to do so. The picture shows exactly the tube I'm talking about. When I put the FD into small ring, clearances are fine. Maybe it differs per frame size and for simplicity they just include it with all frames?
 

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Thanks for posting picture, sorry I neglected to do so. The picture shows exactly the tube I'm talking about. When I put the FD into small ring, clearances are fine. Maybe it differs per frame size and for simplicity they just include it with all frames?
Not sure frame size would make a difference. The front derailleur's place is determined by chainring size regardless of what size frame it's attached to.

You may have a point about simplicity--perhaps it is just a sleeve to reduce friction at the BB bend and it's quicker to install if it's left long. If you can save 10 seconds per task on an assembly line it adds up nicely to a bean counter.
 

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The only reason I can see for that tube is to reduce friction a bit under the bottom bracket.
 

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Discussion Starter · #8 ·
The thing is that it isn't being strapped around the bb. It's just loose right there below the clamping nut.
 

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The thing is that it isn't being strapped around the bb. It's just loose right there below the clamping nut.
Well, maybe sleeve slipped out of the guides after a millions shifts.

If its supposed to be a liner to reduce friction, have to wonder how much slop it introduces in the cable. :nono:

Seems like a funky way to save scratching the cable guides under the BB, if that's why its there. The guides are replaceable, right?
 

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This tube is supposed to start life inside of the frame. When I build bikes it does anyway.

The purpose of this tube/sheathing is to protect the frame from the cable. On most bikes the hole the cable exits out of is very small. The cable comes out at an angle towards the derailleur and is under very high tension. The cable can and will wear right into a carbon frame and deform that hole, maybe alloy too?

Problem is that even when this tube starts life partly on the guide itself, it always moves up. Eventually it moves up enough were it clears the hole and gets trapped floating between the frame and mech doing nothing. It belongs back down into the frame most of the way, but try to get it back down there. If you manage to it'll just work it's way back up and out again.
 

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Discussion Starter · #12 ·
So in most cases I would agree, the problem here is that I've seen two shops build their Cannondales with the tube loose, and wim appears to have a stock photo of the tube loose (above in thread). Which makes me think it's not the typical "anti-friction" tube.

Is it just poor builds from multiple shops or some useless "protector" tube akin to a dork disc? I'm going to check out a 3rd local Cannondale dealer when I pass by it and if they also leave it loose I'm going to ask about it, stay tuned...
 

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Discussion Starter · #13 ·
Went to another shop that does Cannondale, and at this one for some of the bikes the tube was wrapped around BB and tight, while still sliding around on others.

This is what a mechanic at the shop said: The tube comes from the factory, and it is indeed for reducing friction around BB but also for protecting carbon frames. He said on alloy frames the way the guide is it's not necessary to wrap the tube around BB but still comes as part of the bike. He said for an alloy frame you could just cut it off with a razor blade and forget about it. I don't know if it's true or not, but that's what I was told.

Well even though my father-in-law has a CAAD12 I decided to wrap it around the BB, no ill effects and in theory should make the guide piece last longer so that's the way it shall be for now.
 
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