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Chain Length Sizing

Old 09-14-06, 07:09 AM
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CRG
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Chain Length Sizing

Today I'm getting a new chain and I am going to size it according to this article from Park Tool, Chain Sizing by Equation. However I wanted to check to be sure I do this right because I have a double chainring up front and I am pretty sure this was written from a stand point of having 3 chain rings up front. I think I will just go ahead and size it as if I had 3 with a 44 being the big ring. Do you guys see any reason not to do so?
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Old 09-14-06, 07:28 AM
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Yes, the equation method will work, I'd suggest the "simple equation" listed. Doesn't matter if you're using a double or triple crank, the point is to have the chain long enough for all possible gearing combinations, including big ring/largest cog, but at the same time not have a chain that's too long. The equation method will take care of this, and keep you from breaking something if you have a brain lapse and run the big ring/largest cog-

Last edited by well biked; 09-14-06 at 07:37 AM.
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Old 09-14-06, 08:35 AM
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The equation method seems like too much work. I put the chain on the largest cog and ring (without threading through the rear derailleur), size, and remove links. This whole process takes way less than one minute.
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Old 09-14-06, 11:38 AM
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Originally Posted by thomson
The equation method seems like too much work. I put the chain on the largest cog and ring (without threading through the rear derailleur), size, and remove links. This whole process takes way less than one minute.
That's how I do it. Add two links (1") to the distance around the largest cog/ring, and remove the rest.
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Old 09-14-06, 12:22 PM
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I used the formula - it's not really too much work, but halfway through I realised that it's just a formula for the exact same thing as physically wrapping your chain around the biggest cog and biggest chainring and adding an inch.

(The distance between axle and bottom bracket x 2) + (largest cog toothcount / 4 (2 teeth per inch, half of cog wrapped by chain)) + (largest chainring / 4) + 1 inch

I felt better knowing that - and knowing that it came out to the exact same value.

The more complex formula is the same formula too, but takes into account the angles between chainrings and cogs and the extra wrap because of that.

-Scott
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Old 09-14-06, 12:40 PM
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If I'm putting a new chain on a bike that I know has a properly sized chain on it already, I just take the old chain off and lay the new chain down alongside it and cut the new chain to length. And of course the method of putting the new chain over the big ring and large cog and sizing it that way works, too. But in my original answer I was mostly addressing the OP's concern about whether it would matter, using the "formula method", if his bike is equipped with a double or triple crank-
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