Finding the correct chain length

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Gabbo
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Finding the correct chain length

Postby Gabbo » Thu Jan 17, 2013 19:10 pm

I've recently changed the cassette and chain on my bike, with the cassette now being 11-23 opposed to the 12-28 I previously had. Everything has been setup (by myself of course) but I am looking to decrease the length of the chain. I've got all the required tools to do the job, but my concern is how many links do I remove?

When the bike is setup to small/small combo, the chain is slack and rubs against the chain stays. In the big/big combination it tends to function without any disruption.

So anyway, I watched this video on how to correctly size your chain. I can't help but think that the chain is way too tight in this big/big combo as the lowermost jockey wheel from the rear mech is pulled all the way forward. Has this dude allowed even a little bit of slack in this set up?

Watch: http://www.youtube.com/watch?v=lyn7fxHDV-M

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smidsy
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Re: Finding the correct chain length

Postby smidsy » Thu Jan 17, 2013 19:18 pm

Shimano size chains in big front big rear and say add 2 links.

Alternative is big front small rear and rear mech should be more or less vertical (jockey wheels in line with rear axle).
Last edited by smidsy on Thu Jan 17, 2013 19:27 pm, edited 1 time in total.
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nicklouse
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Re: Finding the correct chain length

Postby nicklouse » Thu Jan 17, 2013 19:19 pm

i use the big and big rings/cogs and add a full link (1") for MTB or Road bike.
that guy seems to have missed a bit out when talking about the jockey wheels being aligned (as they always are).

have a read on how Shimano say it should be done.
http://techdocs.shimano.com/media/techd ... 611842.pdf
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smidsy
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Re: Finding the correct chain length

Postby smidsy » Thu Jan 17, 2013 19:22 pm

Both jockey wheels - so just as shown in the 90 degree picture on the attachment you kindly posted.

Sorry for poor wording.
Last edited by smidsy on Thu Jan 17, 2013 19:28 pm, edited 1 time in total.
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MajorMantra
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Re: Finding the correct chain length

Postby MajorMantra » Thu Jan 17, 2013 19:26 pm

The quickest way in my experience (and they way we did it at my old work) was to thread the chain through the rear mech and put it in small/small. You then remove enough links to allow the chain to clear the rear mech.

Effectively this gives you the longest possible chain that won't foul in any gear. If you're operating at the limits of mech capacity, I'd consider more rigorous methods such as the equation given on the Park website.

Gabbo
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Re: Finding the correct chain length

Postby Gabbo » Thu Jan 17, 2013 20:03 pm

Right, I've now removed a few links and set it back up. Whilst the chain is now avoiding the rear mech when in small/small combo, when in big/big, the rear mech automatically switches back down to the small chain ring. Any reason why this could be?

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MajorMantra
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Re: Finding the correct chain length

Postby MajorMantra » Thu Jan 17, 2013 20:05 pm

Will it stay in small front/big rear? Could just be the (low) limit is set too far in.

Gabbo
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Re: Finding the correct chain length

Postby Gabbo » Thu Jan 17, 2013 20:19 pm

MajorMantra wrote:Will it stay in small front/big rear? Could just be the (low) limit is set too far in.


Yep, it definitely stays in small front/big rear; however, it doesn't even enter the 11t sprocket when on the big chain ring. Is this just a case that the rear mech needs adjusting?

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smidsy
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Re: Finding the correct chain length

Postby smidsy » Thu Jan 17, 2013 20:21 pm

MajorMantra wrote:Will it stay in small front/big rear? Could just be the (low) limit is set too far in.


Limit screws only limit the mech travel in and out so once they are set to the correct extremities (in line with the biggest and smallest cog on the casette) they should never be moved. If it went through the full range before it should now.

However, if you can not access the 11, it may need the limit screw turning to allow it to travel further towards you.

Also have you adjusted the B screw. You need to have about 2 links space between top jockey wheel and cassette.

Edit: just read that it goes in the 11 when on small front but not big front so do not adjust the limit screw.!!!
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Froomes Edgar
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Re: Finding the correct chain length

Postby Froomes Edgar » Fri Jan 18, 2013 08:20 am

MajorMantra wrote:The quickest way in my experience (and they way we did it at my old work) was to thread the chain through the rear mech and put it in small/small. You then remove enough links to allow the chain to clear the rear mech.

Effectively this gives you the longest possible chain that won't foul in any gear. If you're operating at the limits of mech capacity, I'd consider more rigorous methods such as the equation given on the Park website.


Exactly right. Then, should one be unfortunate enough to have a chain malfunction when out riding which necessitates the removal of a link, you'll still have enough chain to use every gear.


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