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Crank and chainline problem

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Crank and chainline problem

Old 07-08-13, 04:05 PM
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Banzai
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Crank and chainline problem

Here's a problem brought on by technology.

First, I realize that the easiest solution is probably to find a square taper compatible crankset, but let's try to work with what I have.

Looking to fit up a Deore M590 two-piece HTII crank to a touring-style bike.

However, chainline is 50mm, and so far I can't get a Tiagra 4500 triple FD to swing that far.

And the MTB FDs, near as I know, won't work with road shifters.

So...thoughts?
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Old 07-08-13, 04:29 PM
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First of all, is there any way to move the crankset inboard, ie is there enough chainstay clearance?

Then, the question of derailleur swing can often be worked around if you have a band mount FD. Manufacturers use the identical FD geometry an all their band mount FDs (of the same model range), so the smaller the seat tube diameter the shorter the outboard reach of the FD. (This is the real reason Campagnolo discontinued 1-1/8" clamp Record FDs). So if you have a small seat tube, you can increase the outboard travel by using a larger clamp derailleur and a shim.
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Old 07-08-13, 05:00 PM
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Good ideas there. However...

Rearranging the spacers on the BB cups will result in sub-optimal, even dangerous, thread engagement. Or too much spindle on the left side to be able to clamp the left crankarm on securely.

Also, seat-tube is large diameter already.

Oh, the problems of new tech...
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Old 07-08-13, 05:27 PM
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Originally Posted by Banzai View Post

Oh, the problems of new tech...
Mechanics whove been around long enough remember the long slow process of bikes becoming somewhat standardized. That process ended about 15-20 years ago, and now just about any modification sets off ripples of complications.

However, I believe (don't bet your life on this) that there is a mtn FD/road lever combination that works. I forget if it's a mtn FD with road pull response, or a road lever made for mtn FDs. But, with any luck, a Shimanophile will see your plight and lead you in the right direction.
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Old 07-08-13, 07:07 PM
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Originally Posted by FBinNY View Post
Mechanics whove been around long enough remember the long slow process of bikes becoming somewhat standardized. That process ended about 15-20 years ago, and now just about any modification sets off ripples of complications.

However, I believe (don't bet your life on this) that there is a mtn FD/road lever combination that works. I forget if it's a mtn FD with road pull response, or a road lever made for mtn FDs. But, with any luck, a Shimanophile will see your plight and lead you in the right direction.
I figure that's probably my option. I've been Googling the heck out of it (why does that sound dirty?) but have come up with nothing. I suppose I could try to file off some material from the inside of the limit stop on a road front mech, and extend the travel that way...

I've found historic threads on BF where people have used this very crank combo. I'm a pretty good wrench, and I can't get my front road mechs (designed for 47.5 chainline) to swing far enough to make this work. Very frustrating.
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