Chain Length

Mtventoux said:

THe Mechanic at the shop told me a way to check for proper chain length, but I forgot. Basically, my chain rubs or slaps against the front der. any time I am out of the saddle, so I am thinking it is too long. Does anyone have any tricks to determine this?

That's not the chain causing the problem. You need to adjust the limit screws on the FD.

Well, I thought of that, but they are positioned pretty well. The chain only rubs out of the saddle when the bike is swinging, and then the chain hits both sides of the front der. as the bike swings....so slaps the chain. When sittind down pedaling along, it is fine and does not rub.

Mtventoux said:

THe Mechanic at the shop told me a way to check for proper chain length, but I forgot. Basically, my chain rubs or slaps against the front der. any time I am out of the saddle, so I am thinking it is too long. Does anyone have any tricks to determine this?

Remove the chain and wrap it round the larger chainwheel and the largest cog, without it passing through the rear derailleur. Pull it taut and overlap the two ends by one link and that should be the correct length.
I can't see how the chain length will affect the front derailleur though.

Mtventoux said:

Well, I thought of that, but they are positioned pretty well. The chain only rubs out of the saddle when the bike is swinging, and then the chain hits both sides of the front der. as the bike swings....so slaps the chain. When sittind down pedaling along, it is fine and does not rub.

Sounds like a loose BB.

hd reynolds said:

Sounds like a loose BB.

Or bottom bracket frame flex. What kind of bike?

Mtventoux said:

Well, I thought of that, but they are positioned pretty well. The chain only rubs out of the saddle when the bike is swinging, and then the chain hits both sides of the front der. as the bike swings....so slaps the chain. When sittind down pedaling along, it is fine and does not rub.

Well, as someone else mentioned, it'd be worth your while to check the BB cups, but I suspect if the BB was loose you might also hear some knockings. Still, that's an easy check. You can't do anything about flex at the BB shell. And even though, you say the FD adjusted fine, you still might try futzing with the limit screws: you might be able to increase the FD range of movement and still be able to maintain good shifting and avoid dropped chains.

Mtventoux said:

THe Mechanic at the shop told me a way to check for proper chain length, but I forgot. Basically, my chain rubs or slaps against the front der. any time I am out of the saddle, so I am thinking it is too long. Does anyone have any tricks to determine this?

Go to the Shimano website and look around for a test you can do to determine correct chain length, WITHOUT removing the chain. Think it is in their rear derailleur docs.

simple check first -- shift to your small ring, and small cog in the rear; does the chain "droop" in the middle under the stay? or: big ring front, biggest cog rear -- is the rear derailleur flexed out almost as far as it will go? if test #2 is yes, you're ok on chain length and need to check the bb. if test #1 is yes, look at shortening the chain.