Bicycle Mechanics - Chain Length, Big Problems

Well, I recently upgraded the compenents on my 17" 2000 Cannondale F300. I put on:

Shimano XT rear derailleur
Shimano LX front derailleur
Shimano LX crankset
Shimano LX shifter set
Shimano LX cassette

My brother bought a 18" 2002 Cannondale F500 and after a few weeks there were some major tuning problems. His chain was either too loose or too tight because in order to remove a link from a chain, you have to remove two. When the chain is too loose, it tends to fall off a lot and the chain rubs on itself at the rear derailleur. When the chain is too tight, the bike does not shift into the most extreme position (largest chainright, largest cassette sprocket) properly, and when it is in that position the gears on the rear derailleur are horizontal. If he could remove just one link somehow, the chain would be the proper length. He has the same components as I do, except his cassette is a Shimano Deore and has 34 teeth on the largest sprocket (mine has 32). So, we have figured out that it is either the fact that his cassette is larger or because his frame is larger that his chain cannot be properly sized when mine is the perfect length. Does anyone know how we can fix this problem?

Put the chain in small and small. Look under the top pulley on the derailleur. If the chain is very close or touching itself when it goes around that pulley, then it is too long. If its too long and you take 2 links out it isnt going to be too short...............

that is the thing though.... it does touch itself but when two links are removed, the chain becomes too tight.

Matt,

You don't want to be in the large chainring large cog, too
much cross chaining and not a good thing.
If the chain is correct lenght for all other gear combo's I
wouldn't worry about it.

Marty

Well, I would just except that the problem is unfixable, except my bike works flawlessly with almost the exact same configuration. It isn't really that it is something needed to work, but it should, so it is irritating that it doesn't on one bike when it does on another.

Maybe you need a rear derailleur with a longer jockey wheel brace (I don't know the right name for it). It's the brace that holds the two jockey wheels apart. A longer brace will take up more slack in the chain when your in the small/small combo.

did you buy a short or long cage XT derailure. a lot of mail order stuff is unused OEM buy outs, you really have to know what you're buying. The long cage is needed to do the 34 tooth cassette, the short will do 32 teeth at a stretch. I use an XTR long cage on a touring bike with a 53 up front and a 34 XTR on the rear and if works fine and I can shift the full range of gears with the correct amount of chain tension.

An Mtb with a large cage derailleur offers generous latitude when it comes to chain length. Plus or minus a link should not cause problems. You can buy half-links, but in you case this is absolutely not necessary. Besides, there is a difference between your two bikes in wheelbase distance.

Dude... you shouldn't be shifting into gear 3 - 1 with any bike... that's absolutely *horrid* on your components...

Put it into middle gears, and check the chain. Take out a link or two where necessary... tell your bro not to use 3 - 1... and don't look back.


I have mine so right that the rear derailleur is like 2.5" from my chainstay in gear 2 - 1 (but I dont have a 3rd ring). It keeps the chain from slapping so much, and it shifts smoother.

Thanks guys, that's the word I was looking for......."cage".

Joker22 is my bro. Sorry about that. It was me posting, but he forgot to log off his user-name.

It isn't really that it is something needed to work, but it should, so it is irritating that it doesn't on one bike when it does on another.

When you are in 3-1 look down to see the flex and stress you are putting on your chain. You should not use this gear combo.
I am guessing your chain is "stretched" and needs to be changed.

I am thinking that your chainlines could be different and that is also why it does not work. When using extreme gears chainline gets to be more important.

Click HERE (http://www.parktool.com/repair_help/clg2.shtml) to check your chain line.

I'm guessing that the derailleur tension screw needs adjusting. Unless you did something silly like putting on a mega-range cassette less-than-long cage derailleur upgrade, you shouldn't have the jockey wheels hitting the cassette (or the rest of the derailleur), even in the "no-no" small-small combo.

What you should do is find the derailleur tension screw-it's the one which adjusts how far the derailleur pivots forward and backward. Adjust it so that the chain is just far enough away from hitting things, then see if everything else works ok. If not, go on to the next step:

Now, as far as getting the correct chain length-here is the quick, easy, sure-fire way to do it: Run the chain around the big-big combo (through the derailleurs, too!), and see where the absolute tightest point is where the ends cross. As long as the first possible join is more than 1/4 link away (a link is both inner and outer pieces, btw. 1 link = 1"), join the chain there. If it's less than 1/4 link away, go to the next link. FWIW, there are half-links available, but only in track chain sizes.

From what you have described, though, he likely needs to either go back to a 32 tooth, or maybe keep the 34, but have a larger small cog. Or, he could upgrade to a longer cage rear derailleur, one which has greater capacity. A bike shop should be able to help you out.


When you are in 3-1 look down to see the flex and stress you are putting on your chain. You should not use this gear combo.
I am guessing your chain is "stretched" and needs to be changed.

I'm sorry, but this advice makes no sense at all. You should disregard this-the chain is not stretched, and you will never be able to visibly see flex in a chain.

Originally posted by captsven
I am guessing your chain is "stretched" and needs to be changed.

Huh?...!

When you use the extreme gears Big ring/big cog and small ring/ small cog the chain has to flex the most laterally.

If you sit on your bike and look at the chainline you can see how the chain leaves the cog and chainring in a straight path and then bends between the rings and the cog. This puts alot of stress on the chain in these extreme gears.

If your chainline is off (lets say the small ring lines up with the middle of the cassette) then the chain has to go that much farther if you are in the big ring/big cog combo. This will put even more stress on the chain.

A new chain will not have as much lateral play as a worked in one. So a new chain may not work in the extreme gears if the chainrings are shifted outward. Most of the gears will work fine but some won't.

Originally posted by matt719
It isn't really that it is something needed to work, but it should, so it is irritating that it doesn't on one bike when it does on another.


It isnt something that is needed to work, AND IT SHOULDENT. You should NEVER shift to big big, EVER.

You should never be in big/big or small/small so what difference does it make if the chain rubs on the cage when its in small/small? You'd surprised at how many bikes do this out of the box. You can always turn the angle adjusting screw in a little to see if helps but be carefull not to trun it too much. Dont go to far beyond parrallel with the chainstay or 'ghoststay' if your model doesnt have them

If his chain is falling off it either chain alignment, which I highly dought on a new bike, or the derailleurs need adjusting.

As far as the difference between your bikes you did mention that your frame sizes are different. I dont have Cannnondale literature but it is possible your chainstay lengths are different.