# Sizing the chain length on a downhill rig



## FrankRizzo (Mar 8, 2009)

Hi,

I building my first downhill bike and have a question regarding chain length. Previously I've always had bikes with three chain rings at the front and drill was always something like "measure big cog to big ring, without going around the rear mech cage and add one or two links".

Then you would put the chain on the small ring at the front to gain some slack while you adjusted the rear mech.

This technique doesn't seem to work with a single chain ring at the front as the chain ends up too short once threaded around the cage so I was wondering what the correct procedure is in this situation?

I'm building a 2012 Demo 8 II with a 36t front ring, SRAM X9 10sp mech - short cage - and 11-26t cassette.

I appreciate any help you can offer.


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## The Grimmer (Oct 20, 2010)

Mine was too short when I got it, the rear mech was getting caught in my biggest cog. So I added just enough so it didn't, and it's fine now 
I just go with: have it as short as possible so that it all works smoothly.


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## scottvt (Jul 19, 2009)

Take out the rear shock and use a strap to hold the rear wheel to the frame in the fully compressed position and setup the chain length in that position to account for any chainstay growth when the suspension cycles. Also I usually put the chain in the big/big combo, regardless of how many rings are up front, and run it trough the rear derailleur, but pull it tight so its close to bottoming out, but not bottomed. That way you you will always have enough chain regardless of your gear combo and suspension travel.


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## kenbentit (Jan 2, 2003)

Yeah, the method scott recommends is the most foolproof way to make sure you get it right. Going big to big works pretty well but some longer travel bikes have a fair amount of chain growth as they go thru full travel so it's smart to check it at full compression. Nothing like ripping your der. off in a G-Out (yes, I've been there )


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## Tim F. (May 22, 2006)

scottvt said:


> Take out the rear shock and use a strap to hold the rear wheel to the frame in the fully compressed position and setup the chain length in that position to account for any chainstay growth when the suspension cycles. Also I usually put the chain in the big/big combo, regardless of how many rings are up front, and run it trough the rear derailleur, but pull it tight so its close to bottoming out, but not bottomed. That way you you will always have enough chain regardless of your gear combo and suspension travel.


I think he meant to say, Take the Coil of your shock, and strap it down so that it's fully compressed..." I made the mistake of not checking my chain length after switching to a larger cassettt and a brand new Saint deraier, and snapped the derailer right off on the 1st run. Bummer!:madman::cryin:


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## kenbentit (Jan 2, 2003)

That's EXACTLY what I did! Mangled that sweet Saint der beyond repair....


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## Clutchman83 (Apr 16, 2006)

On a 1x9 I've always just set it so the derailleur is fairly taught while in the biggest gear on the cassette. Starting from zero I install the chain as is and then just remove links until I get the derailleur extended but not maxed out. It's a visual system so can't give specific lengths due to frame differences. Main thing is you want to leave a bit of play in the derailleur when in the lowest ratio (largest cog). As long as it isn't all scorpioned up and curled back when you get to the top gear you'll be good!


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## essenmeinstuff (Sep 4, 2007)

I usually take spring out and or dump the air on rear shock, cycle with chain on to see where max growth is, then biggest on cassette (1X9), then make the chain shortest + 1 or 2 links.

Ie basically what scott said.


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## FrankRizzo (Mar 8, 2009)

Thanks for all the feedback. It was a bit of a mission just to size the chain but I followed the steps you described, removing the coil and strapping the rear linkage up to the frame. I removed three of four links from the 114 link chain and it seems to shift fine and isn't too slack. Guess the real test will be when I take out on the trail. At lest next time I'll only need to match the length of the new chain to the old one which will be much easier


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## scottvt (Jul 19, 2009)

The latest Tech Tuesday on PinkBike........Tech Tuesday - Chain Length Basics - Pinkbike.com


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