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Old 11-17-11, 10:06 AM   #1
martyn3200
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Replacement double road FD with long reach

So I recently purchased a compact crankset, but had trouble upshifting. The HL screw was as loose as possible so it was a reach issue. I'd already lowered the FD to the right height angle. In a moment of frustration I tried to crank up the cable tension to try and get it to shift up, and stripped the FD nut when tightening the cable clamp bolt too hard
I presume my bottom bracket is too long. Is that a fair assumption? Anyway, i was wondering if I shimmed on a 31.8 onto my 28.6 seat tube would that enable the FD to reach further.
Your thoughts would be appreciated
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Old 11-17-11, 10:18 AM   #2
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Might be that your BB is too wide- if you changed from a triple to a compact double and used the same BB, then the axle will likely be too long. Measure your chainline (distance from the center of the seattube to midpoint between the chainrings- I don't know the spec for your bike, but 42-45mm is common. This is adjusted by getting narrower or wider axles in the BB.
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Old 11-17-11, 10:41 AM   #3
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Just went from a standard double to a compact double. Would really like to avoid changing the bb
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Old 11-17-11, 12:04 PM   #4
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you stripped the FD, buy one *for that Compact crank, combo.

Quote:
Just went from a standard double to a compact double.
you may have put a lower profile replacement crank on, and thus the chainline moved outboard.

because the crankarm design was intended to use a shorter BB. to maintain the same chainline.

measure the 2, might have to refit the other , to measure it's chainline dimensions


re the shim, an eccentrically arranged shim, perhaps
thinner on the left, thicker on the right, so DIY made, not off the shelf.
for really moving it rightward
your measurement will tell you the difference needed,

+ a band on adapter, to use a Braze on FD*


in for a Pence , soon becomes in for a Pound .. +

Last edited by fietsbob; 11-17-11 at 01:38 PM.
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Old 11-17-11, 12:38 PM   #5
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I also went from a standard double to a compact double on a square shaft spindle and found the chainrings did move outward some. My FD was able to adjust for it. I'd try the shims you describe, I would think that would do it.
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Old 11-17-11, 11:33 PM   #6
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Quote:
Originally Posted by martyn3200 View Post
Just went from a standard double to a compact double. Would really like to avoid changing the bb
Required square taper bottom bracket lengths vary with the crankset.

For instance low profile Campagnolo Record/Chorus cranks used 102mm bottom brackets while the other doubles needed 111.5 regardless of whether the ring configuration was standard (135mm in Campagnolo land) or compact (110/112.5).

Derailleur geometry doesn't vary like that (just with double/triple where the chain line is different)
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Old 11-18-11, 09:21 AM   #7
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Yah, also, there's the issue with JIS and ISO tapers on the axle and crank. I forget which one is which, but even though they have the same angle, the taper is of different lengths. So the wrong crank/axle combo can either bottom out before the bolt is tight, or not engage far enough which could put the chainline out too far. Try measuring the width of the hole on both cranks with an inside caliper. I know, not much help if you're trying to avoid a new BB, but it would be good to know root cause, eh?

Last edited by cycle_maven; 11-18-11 at 09:25 AM.
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