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Chain lenfth question

Old 07-28-20, 07:42 AM
  #1  
trek330
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Chain lenfth question

I'm a little confused about chain length.I've read the formula of measuring a new chain by wrapping around with out going through the derailleurs big front and big back then add 2 rivits.Does this work regardless of long,short or medium cage derailleur?I'm considering changing to a long cage to accomadate a 32t cog and it was suggested I add a couple of links to the chain by 1 or more "professiopnal"What is the consensus?And if so(to add)why isn't it mentioned for example in the Park Tool clip?
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Old 07-28-20, 08:26 AM
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Any technique you use can be checked by putting the chain on the big chainring/big cog and small/small to make sure the derailleur isn't too horizontal for big/big and jockey wheels aren't rubbing against the chain in small/small. Of course cross chaining isn't recommended while riding but sometimes it happens.
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Old 07-28-20, 08:43 AM
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There are several common methods to let you gauge where to break the chain. Some better than others depending on what specific rear derailleur you have and whether 1x, 2x or 3x front.

I'd recommend you search the technical documentation at the website of whomever is your rear DR manufacturer.

If you know what to look for, you can always leave it too long and remove a link at a time till you have it working as good as it can. There is a catch to doing that........ you have to know what you are looking for.
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Old 07-28-20, 08:48 AM
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You must absolutely have the chain long enough to go into the big-big combination or you risk damage to the derailleur or frame. Having a slack chain in small-small will not damage anything.
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Old 07-28-20, 10:25 AM
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Sounds right

Originally Posted by trek330 View Post
I'm a little confused about chain length.I've read the formula of measuring a new chain by wrapping around with out going through the derailleurs big front and big back then add 2 rivits.Does this work regardless of long,short or medium cage derailleur?I'm considering changing to a long cage to accomadate a 32t cog and it was suggested I add a couple of links to the chain by 1 or more "professiopnal"What is the consensus?And if so(to add)why isn't it mentioned for example in the Park Tool clip?
Your formula sounds right, assuming you do it with the cassette you're planning to use (with the 32t cog). If you're using a masterlink just be sure to break the chain on a rivet that leaves both ends of the chain to accept the master link, and make it one rivet longer if you need to to break on the correct rivet. If you're not using a masterlink, why not?!

I did the same thing this spring on a 9 speed with double CR, going from an 11/ 26 to an 11/ 36t cassette, starting with a new chain and a new Sora medium cage RD. It's outstanding, and the formula worked great even with the longer cage (I had a short cage before).

You don't ride on large/ large combo anyway, but you do want the chain long enough to do so on the work-stand, just to test that indexing is all good.
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Old 07-28-20, 11:13 AM
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I agree that the "large-large + 1complete link" approach doesn't account for the chain wrap capacity of the RD, although it seems to work regardless. My "trial and error" method (only works with a reusable master link) is to install the chain on the large/large and shorten it to where I'm comfortable it's not straining the RD. I "clip off" the excess, join it up and run it on the small-small. If the chains is still under tension, and the RD cage isn't up in the sprockets, all good. If not, back onto large-large and reevaluate if I can remove a further link our two without straining the RD. If I can't, then clearly my ring/cassette choice is exceeding the chain wrap capacity of the RD, and it's time to change something. Never happens, of course - my medium cage RD has a chain wrap capacity of 30, and my current setup (39/51F, 12/23R) has a range of 23.
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Old 08-03-20, 08:23 AM
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The question I asked was asked because the setup I had which followed the formula Large,large plus 2 rivets didn't allow the chain to work in the large back and large front combination which I occasionally would stumble into without wishing to.I have a medium cage derrailleur in the back and a triple front chainset.and the large cog in the back is 32T.I was told I needed a long cage derailleur by some people and a longer chain by others.After buying a "Deore MTB long cage derrailleur I was told it wouldn't work with my brifters,Finally I bought a new chain,added 2 rivets in length and the large large combination now works well enough that I don't need to worry if I inadverttently enter it.Not too much slack either in the small,small combo!Thanks for everyones input.
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Old 08-03-20, 08:48 AM
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The formula works regardless of cage length, but it is to add two links, not two rivets.
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Old 08-03-20, 09:41 AM
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My approach is similar to others. Figure a good ďin the ballparkĒ and add a couple links. Run through the gears. On the big-big, Iíll always stop the pedaling and see how much more travel I have on the derailleur stretch.

You have to remember that a chain climbs onto a larger cog/cheinring. In all honesty, Iíve never searched, nor tried to figure out, if there is a point prior to actually seating on a cog/chainring where more chain is needed than when seated. For me, I donít want the derailleur so stretched out that I have almost no margin for error.

John
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Old 08-03-20, 11:10 AM
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One thing I'll add on cage length. While everyone will say, and correctly so, that cage length has nothing to do with chain length, it is referring to the big-big calculation. It does have an impact on the small-small. If you happen to be in that in-between spot where the length you want to use is just a tad bit too long for the small-small, then a longer cage will help.

Unlike the stretched out big-big, the small-small is pulling back away from the cogs/crank and the longer the cage the less it will fold back on itself.

John
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Old 08-03-20, 11:53 AM
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Javascript Bicycle Chain Length Calculator
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Old 08-03-20, 01:36 PM
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Current derailleur chains are only shortened, to lengthen them you get a 2nd quick link & additional chain.

I Only press pins out & in on single speed, where there is no sideways bending of the chain to shift..
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Old 08-03-20, 11:29 PM
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SRAM, Shimano and Campy are all a bit different, so check the manual for your specific drivetrain. Your method sounds like the newer Shimano technique. The latest Ultegra/Dura Ace seem to need a bit more chain length than older versions to work their best and remain quiet.
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Old 08-05-20, 07:31 AM
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The big/big plus one inch method works for most, but not all modern RDs. The new Campy 12 and any other RD with a extension plate that moves the RD back further for large sprocket clearance requires about 1 inch more chain. When I switched from Campy 11 to 12, my chain length was specified by chainstay length, according to Campy instructions and the chain had to be 1 inch longer than before.

I recently switched from a Campy 11-34 cassette to a SRAM 10-36 AXS cassette and had to use new chains that are another 1 inch longer to wrap the big/big. This combo exceeds the RD wrap capacity by 3T.
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