Another chain length question...

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fast but dim
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Another chain length question...

Post by fast but dim »

I am due to remove my short cage, and fit a medium cage rear derailleur to my best bike so I can fit a 32t cassette when necessary ( I'll usually have a 12-27 fitted)

Logic makes me think that the longer cage derailleur will mean I need a longer chain, but as I intend to change cassettes depending on terrain, what do I do? usually ID. Go big to big plus a link... But as I'll either have a 27 or a 32 what's my best bet?
Brucey
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Re: Another chain length question...

Post by Brucey »

I'd keep a chain with each cassette; not because they need to be a given length (although they might), but because that way they will wear together and you won't get any jumping.

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Mick F
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Re: Another chain length question...

Post by Mick F »

There's a lot of leeway in the chain length.
Just changing the rear mech jockey cage length doesn't make much difference.
I went from Medium to Long and the chain length didn't notice.

Using the method you say as big/big + one link is fine. Nothing wrong with adding two links to be on the safe side.
Too much chain is absolutely fine, even if it dangles a bit.
Too short a chain and you'll be very sorry. :shock:
Mick F. Cornwall
fast but dim
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Re: Another chain length question...

Post by fast but dim »

Brucey wrote:I'd keep a chain with each cassette; not because they need to be a given length (although they might), but because that way they will wear together and you won't get any jumping.

cheers


I've got a couple sets of wheels, and on the ball with chain wear, so that's not an issue!
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cycleruk
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Re: Another chain length question...

Post by cycleruk »

fast but dim wrote:I am due to remove my short cage, and fit a medium cage rear derailleur to my best bike so I can fit a 32t cassette when necessary ( I'll usually have a 12-27 fitted)

Logic makes me think that the longer cage derailleur will mean I need a longer chain, but as I intend to change cassettes depending on terrain, what do I do? usually ID. Go big to big plus a link... But as I'll either have a 27 or a 32 what's my best bet?


Just make sure that when the chain is on the big chainring and largest sprocket that it is not tight.
I once made the mistake of fitting a cassette with a larger sprocket and when, accidentally, selecting big to big the chain went on but wouldn't come off either the big ring or big sprocket. :oops:
(A longer rear mech' cage is usually only needed with a triple or a large difference in double chainring sizes.)
You'll never know if you don't try it.
iandriver
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Re: Another chain length question...

Post by iandriver »

Using the largest to largest chain length method, http://www.parktool.com/blog/repair-hel ... -section-3, cage length won't make a difference. The sprocket size will.

As others have said, avoid largest to largest and you'll be fine (Bruceys point about wear accepted, his suggestion is what I'd do). It is easy to make a large to large mistake when fatigued on a very long ride. I guess you could look and see if it's a problem at home one cog at a time.
Supporter of the A10 corridor cycling campaign serving Royston to Cambridge http://a10corridorcycle.com. Never knew gardening secateurs were an essential part of the on bike tool kit until I took up campaigning.....
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Mick F
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Re: Another chain length question...

Post by Mick F »

So long as you can get big/big, you will be fine.
I'd hate to be the owner of a bike with too short a chain and inadvertently select big/big and it won't go.

Chain breakage?
Wheel and cassette knackered?
Frame and rear dropouts knackered?

The prospect doesn't even bear thinking about. :shock:
Mick F. Cornwall
iandriver
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Re: Another chain length question...

Post by iandriver »

Your derailleur will pull straight and stop working. Can take an uncomfortable yank with the wheel nuts loose to free it if you can't split the chain. Who knows what that can break or bend.
Supporter of the A10 corridor cycling campaign serving Royston to Cambridge http://a10corridorcycle.com. Never knew gardening secateurs were an essential part of the on bike tool kit until I took up campaigning.....
Brucey
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Re: Another chain length question...

Post by Brucey »

If you can't use big-big because your chain is too short but you try anyway....on bike with a screw-on freewheel the result is usually a bent or broken rear axle and maybe some frame damage (bent dropouts) too. On a bike with a freehub I think the chain will break or the chainstays/chainrings will crumple or something.

It ain't pretty... I'd sooner have chain slack on small-small than have the chain too short to run big-big.

cheers
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Mick F
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Re: Another chain length question...

Post by Mick F »

Brucey wrote: ............ I'd sooner have chain slack on small-small than have the chain too short to run big-big.
+1

............ maybe +100
Mick F. Cornwall
fast but dim
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Re: Another chain length question...

Post by fast but dim »

Brucey wrote:If you can't use big-big because your chain is too short but you try anyway....on bike with a screw-on freewheel the result is usually a bent or broken rear axle and maybe some frame damage (bent dropouts) too. On a bike with a freehub I think the chain will break or the chainstays/chainrings will crumple or something.

It ain't pretty... I'd sooner have chain slack on small-small than have the chain too short to run big-big.

cheers


good advice :D
BigG
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Re: Another chain length question...

Post by BigG »

With almost any practical triple, the small/small combination is an unnecessary duplicate, and even with extreme gear ranges (60 tooth total on the bike shown) the chain may not go slack. There is of course some rub chain on chain, the chain line is pretty awful and the chain wrap on the small sprocket is minimal, but the gear can be ridden safely which is all that is necessary. As others have said earlier in this thread, the key issue is whether the large/large combination can be ridden safely. Again, it is probably an unnecessary duplicate but sod's law says that you will change into it sometime.
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colin54
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Re: Another chain length question...

Post by colin54 »

I recalled this thread when I read this today, the hazards of a too short chain, got away lightly I think. ...halfway down page....


http://rivbike.tumblr.com/
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Brucey
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Re: Another chain length question...

Post by Brucey »

colin54 wrote:I recalled this thread when I read this today, the hazards of a too short chain, got away lightly I think. ...halfway down page....


http://rivbike.tumblr.com/


...a few days ago I was riding my Cheviot home the hardish way and thought I was in the middle ring, but was actually in the big. I shifted to the 40T ring in back (put on as an experiment) and the chain was a link too short, so this happened:

Image
...The point here is to not be dumb like me. DO make sure there’s slack in your chain when you’re in the big-big. The only way there wouldn’t be is if you did the work yourself and trusted yourself (as I did) to not shift to the big-big....


owwww..... :shock:

cheers
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