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강남 스타일
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Discussion Starter · #1 ·
Setting up a 1x10 with Sram stuff. I know that to determine proper chain length, you wrap the chain around the largest cogs w/out routing through the derailleur and add two links. On my setup this works out to a 52" chain.

However, it's just about one millimeter short of being a magic gear. So if my chainstays were half a millimeter shorter, the procedure would call for a 51" chain.

So my question is, since it's such a small difference can I just go ahead and cut an extra inch off the chain? I'm not using a chain guide and would like to maximize chain tension to reduce the potential for dropping.
 

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??? Why do you care about a "magic gear" when you're using a derailleur? Chain length has no effect on chain tension -- the derailleur spring provides the tension. Even if you have maximum tension when you're in the biggest cog, the derailleur will be taking up more slack in the smaller ones.

The "wrap plus two" is to approximate the minimum length you need to safely avoid busting the der if you shif to big-big. Try running it through the der and see if your hypothetical shorter length still allows a shift to the largest cog without the der being totally maxed out.

I wouldn't go to the minimum length, frankly. With the usual multi-ring setup, a minimum chain length is okay, because you rarely or never actually use the big-big combination -- the extra length is just there to be safe. Since you only have one ring, you will use that combo, and I don't think I'd want it set up so the der is at maximum extension.

From what I've heard, the only way to protect against chain drop on a one-ring setup is with a chain catcher or dummy derailleur in front.
 

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If I had to guess from what you describe, I'd say you could get away with removing 1". However, with it done you need to check what happens as you shift and the chain is climbing from the 2nd lowest cog to the lowest (largest) cog. The RD cage must not go up against a CCW limit of rotation, and the chain should still zigzag through pulleys a reasonable degree and not be stretched straight.
 

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Discussion Starter · #4 ·
I just realized that I could put on a chainring with four more teeth than my current one and check the derailleur operation as you suggested that way, without having to cut the chain. Lucky for me I have a 44t on the bike and a 48t hanging on the wall!
 

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I just realized that I could put on a chainring with four more teeth than my current one and check the derailleur operation as you suggested that way, without having to cut the chain. Lucky for me I have a 44t on the bike and a 48t hanging on the wall!
Yep. That'd work, or grab a length of the installed chain so that you can compress it 1" and see how it looks.
 

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Setting up a 1x10 with Sram stuff. I know that to determine proper chain length, you wrap the chain around the largest cogs w/out routing through the derailleur and add two links. On my setup this works out to a 52" chain.

However, it's just about one millimeter short of being a magic gear. So if my chainstays were half a millimeter shorter, the procedure would call for a 51" chain.

So my question is, since it's such a small difference can I just go ahead and cut an extra inch off the chain? I'm not using a chain guide and would like to maximize chain tension to reduce the potential for dropping.
Actually the preferred method for chain sizing (certainly by Campagnolo) is to put it in the small ring and the smallest cog and remove just enough links to force the derailleur begin to take up chain slack. Running with a shorter chain has a negligible effect on chain tension. Running with an even shorter chain that "just might not be a problem" is a bad idea and certainly accomplishes nothing to prevent chain drop.
 
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