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Old 01-27-12, 08:09 AM   #1
norskagent
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braze-on front der w/ compact crank?

With a braze-on front derailler tab originally positioned for standard road rings, I assume there will be a conflict trying to run a compact crank, that the der. won't be low enough. Any solutions? File the tab slot? Some kind of adaptor? New front der.?
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Old 01-27-12, 08:15 AM   #2
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They typically have a decent range of adjustment. Have you installed both the crank and the derailleur yet or are you only worrying about an issue that may or may not exist?
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Old 01-27-12, 08:19 AM   #3
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I'm pre-worrying, haha. Hopefully it won't be an issue but I wondered if others had dealt with this before.
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Old 01-27-12, 08:21 AM   #4
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Originally Posted by norskagent View Post
I'm pre-worrying, haha.
Ha!

Do tell, what crank/rings/BB spindle are you using and what FD?
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Old 01-27-12, 08:32 AM   #5
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well I was going to wait until the build to reveal...but since you ask, I was the buyer of gioscinelli's merckx 7/11 frame and fork:


and I intend to move the parts from my '89 paramount over to it:

for the most part, I may opt for some different parts, not sure yet.
Crank is a sugino alpina compact w/ phil wood BB. Rear and front der. are dura ace 7400 8speed.
Hopefully robbietunes won't suffer too much angst over the switch, he's familiar with my paramount!
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Old 01-27-12, 08:34 AM   #6
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Cool! Congratulations.

So a 48t big ring? I'll bet you'll be fine. With a crank with lower Q you may have FD cage rubbing issues, but probably not with the Sugino.
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Old 01-27-12, 09:48 AM   #7
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I've never had an issue, but just for fun if you compare the diameter of a 53 vs. a 50 ring, they differ by about 12mm (I calculated this, but I haven't measured it on any actual chainrings). So that means the radius from the BB center to top of ring only differs by 6mm. I would think half a centimeter is something a front derailleur might be able to handle even if you weren't able to move it.
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Old 01-27-12, 09:54 AM   #8
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My compact is 48/34, hopefully not so much to matter.
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Old 01-27-12, 10:02 AM   #9
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Whoops, I used the wrong tooth count. Diameter of 48t ring is approx 195mm (D = 12.75 * T / pi). So difference between 53 and 48 is 20mm diameter or 10mm radius. One centimeter to adjust.
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Old 01-27-12, 10:48 AM   #10
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FWIW I tried to put a compact on my brother's 2300 and the tab was not low enough. 50/34 rings.
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Old 01-27-12, 11:10 AM   #11
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I have an '85 Corsa Extra - which is near identical to op's bike.
My Record crank, w Record BB, has a 49T ring on it.
I'm using a Record FD.

There's still room to move it down more than 2mm.


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Old 01-27-12, 06:25 PM   #12
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I stuck a 50/34 FSA Gossamer on my '86 Cannondale and had room to move the front derailleur (Shimano 105) down.


Seemed to approach the limit, but works fine.
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Old 01-27-12, 11:07 PM   #13
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Quote:
Originally Posted by norskagent View Post
My compact is 48/34, hopefully not so much to matter.
The correct answer is that you may or may not have a problem going to a 48.

That's getting quite a bit smaller than a 52/53, which is generally where the braze-ons were centered. However, that positioning assumed a front derailleur "drop" so the derailleur that you use may be a factor also.

Try it and see (is the only way to determine whether it will work or not...).
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Old 01-27-12, 11:52 PM   #14
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I bought an adaptor from a trek dealer for a few bucks that worked great. It was a listed part for an early trek 5000. I don't remember what it looked like or if it would work on steel.
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Old 01-28-12, 09:33 AM   #15
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I think this would work (if necessary)...~$9
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Old 01-28-12, 09:47 AM   #16
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The Campy tech spec for positioning the FD tab shows a 10mm difference between the position optimized for a 48 vs 53. I don't see a reason for Shimano to need anything different The slot in the tab is probably 20mm so you probably won't have a problem. Worst case, you might have to file a little bit but I'm betting you won't.
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