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Old 07-17-07, 01:26 AM   #1
electricaltape
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drivetrain question

hello,

can someone enlighten me as to what is the reason behind a chain line that tapers toward the chainring instead of the cassette?

really low gearing? does it have to do with the rear derailleur?

the bike below isn't mine. just to illustrate the kind of chainline i have most of the time... using the middle 38t chainring (i have a triple). the chainline gets mostly parallel when using the larger chainring.
this is a large aesthetics matter for me, but i'm planning on switching to a compact crankset and would love to have a chainline that tapers toward the rear.
my rear derailleur is deore.

thanks.

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Old 07-17-07, 06:05 AM   #2
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You have 3 options (in order of increasing cost):
- Let the aesthetic go in favor of function on this one, (0$)
- Go singlespeed (few $ for the conversion, but you only have one speed)
- Go to an internally geared rear hub (many $, but your aesthetic desires will be met and you'll still have multiple speeds)


Without going into a lot of detail, it's a result of using a derailleur gearchange system. Can't be helped with your current set-up.
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Old 07-17-07, 11:53 AM   #3
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Look up the definition of "chainline". It doesn't mean what you think it means.
http://sheldonbrown.com/chainline
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Old 07-17-07, 11:55 AM   #4
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after some researching, i've come to understand that my low-geared cogs (goes down to 32) are the reason. the very low gear extends to a longer rear derailleur cable.. meaning really extended jockey part.... that's what i got from some readin.

i will be changing crankset anyhow... going down to a double.. guess i will have to get a higher geared cogset also?

this is me trying to put a bunch of lipstick on an ass.. the more i ride, the faster i want my bike. there's only so much i can do to a touring frame... but it's what i've got.
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Old 07-17-07, 11:56 AM   #5
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Quote:
Originally Posted by DMF
Look up the definition of "chainline". It doesn't mean what you think it means.
http://sheldonbrown.com/chainline

yes, yes... i'm not sure how else to describe the "other" chainline i speak of. cheers.
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Old 07-17-07, 12:16 PM   #6
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The reason for the long derailleur cage is to wrap more chain, to avoid slack in the chain. Chain wrap capacity is based on the difference in largest and smallest chainring sizes plus the difference in largest and smallest cog sizes.
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Old 07-17-07, 12:31 PM   #7
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Quote:
Originally Posted by electricaltape
after some researching, i've come to understand that my low-geared cogs (goes down to 32) are the reason. the very low gear extends to a longer rear derailleur cable.. meaning really extended jockey part.... that's what i got from some readin.
No. Cog size has almost nothing to do with it, nor does cable length. The thing on the bottom of the rear dérailleur is the tension arm or cage. You need a longer cage to handle a triple crank (as noted above).

If you go to a double, you can use a shorter cage which will help your "problem" a little, but the problem is really in your head. Try to widen your aesthetic to include function. A perfectly functioning machine is beautiful. To make it less functional so it "looks better" to someone is to practice evil.
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Old 07-17-07, 12:38 PM   #8
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Forget the derailleur. Some cogs are larger than the chainring.
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Old 07-17-07, 05:44 PM   #9
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Here's how to fix it:

While the cranks are turning,
1) Shift front derailleur to big chainring.
2) Shift rear derailleur to smaller chainring.

At this point, if the lower portion of the chain (as in the photo above) is still sloping, your chain may be too long. Keep in mind that the angles here don't effect efficiency at all, but the angle the chain makes when viewed from the top does a little. That's what's actually called chainline.
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Old 07-17-07, 08:40 PM   #10
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The reason for the long derailleur cage is to wrap more chain, to avoid slack in the chain. Chain wrap capacity is based on the difference in largest and smallest chainring sizes plus the difference in largest and smallest cog sizes.
*long (short) derailleur cage* was the terminology i needed. i googled and wahlah! came across drew saunders' lovely little page about running a short cage with a triple. interesting.. but i will definitely be switching to a compact double crank and higher/tighter cogset.

tossing my tour gearing wouldn't equate to losing functionality for me. much more the opposite. i never use my granny or the lower cogs. with the bike *feeling* a tad big for me (maybe it actually is a tad big for me), i'm trying for what i can to make it seem less like i'm driving a boat

you are probably right about the "problem" being in my head. it's not a necessity for me to pay so much to switch out something fine. on the same token, i could go the rest of my life without buying another shirt. i could always play my cello strings until they are unable to hold a pitch. i could brew those coffee grinds that have been in the cupboard for a few years. i think building my bike up is something i'd truly enjoy in a worthwhile way. i like giving in to evil. i think if i were truly "evil", i'd go fixie.

thanks to all for all the help!
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Old 07-18-07, 09:30 AM   #11
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Quote:
Originally Posted by electricaltape View Post
*long (short) derailleur cage* was the terminology i needed. i googled and wahlah! came across drew saunders' lovely little page about running a short cage with a triple. interesting.. but i will definitely be switching to a compact double crank and higher/tighter cogset.

tossing my tour gearing wouldn't equate to losing functionality for me. much more the opposite. i never use my granny or the lower cogs. with the bike *feeling* a tad big for me (maybe it actually is a tad big for me), i'm trying for what i can to make it seem less like i'm driving a boat

you are probably right about the "problem" being in my head. it's not a necessity for me to pay so much to switch out something fine. on the same token, i could go the rest of my life without buying another shirt. i could always play my cello strings until they are unable to hold a pitch. i could brew those coffee grinds that have been in the cupboard for a few years. i think building my bike up is something i'd truly enjoy in a worthwhile way. i like giving in to evil. i think if i were truly "evil", i'd go fixie.

thanks to all for all the help!
You sound like a guy ready to upgrade to a road bike. I'd think twice about spending the money on a drivetrain upgrade on this bike.
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Old 07-18-07, 10:35 AM   #12
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aye... but i am saving up for a custom steel for the next one (funny dreams, i have). i do live near some awesome builders. well that and i've been craigslisting it for the right frame... which might or might never pop up. i could easily spend at least a couple more years with my current before adding to the brood.

i've set apart 250 for the new drivetrain. i can do it.
last but not least, i'm madly in love with my current bike.... the frame, that is. it's gonna be a lifer with me... but i got it stock and that has always made me itch. i just couldn't devote the time to build up from the start.
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Old 07-18-07, 11:13 AM   #13
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I'm perplexed at your obsession over chain "shape." It takes a certain shape based on the gear ranges you've chosen to support (some require longer cages). Adapting your gearing to accommodate a specific shape makes no sense to me, although it reminds me slightly of my wife's approach to shoes (don't care how comfortable or functional they are --just how they look).
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Old 07-18-07, 11:47 AM   #14
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Function can sometimes *be* appearance. What other function does a painting have, for instance? Or high heels — they aren't worn for seeing over crowds...


elctricaltape, you need a professional fitting. Get on a well-fitted frame and the love for your current bike may pale.
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