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Old 09-28-09, 08:57 AM   #1
mconlonx 
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Importance of chain line?

Searched, the track forum, but couldn't find anything too useful.

How spot-on should one's chain line be? We have a (brand new) track bike in the shop, as shipped from the mfg. The crank actually does not look like a dedicated track crank, with the chainring on the outside, and spacers used to take up room on the reverse side where there are shoulders for what would be an inside chainring. Crank has through axle on the drive side; BB is outboard bearings.

As the bike is set up out of the box, chain line is off 4.5mm to the outside at the crank. Is this an issue for track use? I know the SS/FG crowd throw conniption fits about this kind of thing. If the chainring is placed on the inside, it's a bit better, only off by about 3mm on the inside. But my understanding is that this is still considered way too far out to be legit, and besides, makes a farce out of any claim of the bike having an actual "track" crank.

What's the dealio? Would you actual track racers be as thrown off by a chain line that far out from the factory?
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Old 09-30-09, 09:34 AM   #2
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Yeah. The FG crowd thinks that a chainline has to be spot-on in order to withstand the terror of the streetz and stuff like that, but the reality is that there can be fudge room. 3mm is really small. The issue here, though, is that this is something coming from the factory - if it's a track bike, not just a consumer-grade fixed gear bike, the parts should be both decent enough and compatible, so that you get a 42.5mm(ish) chainline.

It sounds like they specced some cheap parts, put the chainring on the outside of a road double, for looks, and didn't bother with chainline stuff. As a rider I'd happily ignore 3mm of chainline difference, but as a buyer or critic or something, that would peeve me.
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Old 09-30-09, 10:02 AM   #3
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Out of curiosity, is the chain 1/8 or 3/32? Derailleur chains and chainrings (3/32) are far more tolerant of a bad chainline, and are often used on entry level track bikes like the Bianchi Pista and Felt TK3. Also, many lower end "track" cranks like the Sugino RD are simply road doubles with the inner chainring removed and maybe shorter bolts. They work fine if the correct spindle length is used on the drive side. I agree with Queerpunk that it sounds like your "track" bike was carelessly cobbled up from mismatched parts.
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Old 10-06-09, 04:21 PM   #4
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Quote:
Originally Posted by TejanoTrackie View Post
Out of curiosity, is the chain 1/8 or 3/32? Derailleur chains and chainrings (3/32) are far more tolerant of a bad chainline, and are often used on entry level track bikes like the Bianchi Pista and Felt TK3. ... I agree with Queerpunk that it sounds like your "track" bike was carelessly cobbled up from mismatched parts.
1/8" chain.

Not priced like an entry level track bike, but the only one in the lineup.

I'd agree with the last part, though. Measured, the crank is set for a chainline of about 49.3; hub is traditional 120mm width at the dropouts, 42.5 chainline. Hmm. If this is all correct, then moving the chainring to the inside, 7.25mm, should just about do the trick. Still be off by about half a mm.

Still...

A "track" crank where you have to swap a chainring to the inside set of shoulders, with some spacers on the outside and double-length chainring bolts, just to get proper chainline...?
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Old 10-07-09, 10:32 AM   #5
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What bike is it?

Are you able to move the chainring inboard of the spider without hitting the chainstay?
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Old 10-07-09, 12:44 PM   #6
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If you like to run your chain with some noticeable slack you should have a reasonably good chain line. I don't know if being off by 4.5mm is bad or not for this situation.
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