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Old 05-01-07, 08:59 AM   #1
Collie
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front derailleur query

hi,

I have finished my bike build about two weeks now, and i am tweaking my setup here and there to tune the bike up nicely.
So about my front derailleur:

the frame-set is the Thorn Sherpa with the stock BB installed by Thorn.
the crankset is a Sugino xd600
the FD is a Shimano LX (2006/2007 model i think) suited for a 31.8mm seat tube.

the seat tube on the Thorn Sherpa is 28.6mm.

I am using a shim to mount the 31.8mm FD to the 28.6mm seat tube. but i am getting some rubbing when i am in the lowest gear combo.

So my question is:
if i were to install a FD whose size was 28.6mm in diameter (thereby not needing to use any shims) would the FD sit closer to the seat tube therefore eliminating any rubbing????

see attached picture of the bike!!!
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Last edited by Collie; 05-01-07 at 09:05 AM.
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Old 05-01-07, 09:26 AM   #2
DevLaVaca
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It probably would. It's always tricky using different sizes, especially for the FD. Have you tried putting shims only on the left side? This might help snug the derailleur up to the seat tube, but, with a 3mm difference, you'd have to be careful to not compromise the strength of that mounting.
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Old 05-01-07, 01:30 PM   #3
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I assume you've tried adjusting the low limit screw? Sheldon Brown has a good write-up here: http://www.sheldonbrown.com/derailer-adjustment.html. Maybe you can adjust it so you get no rubbing in the lowest gear (which you'll likely use on tour) but you will have some rubbing in the highest gear (which you're less likely to use)?

You're bike looks a lot like the one I'm building up. That's an interesting looking handlebar bag, care to elaborate on it? How is it mounted?
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Old 05-01-07, 09:43 PM   #4
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hi,

yes i have adjusted the H and L screws to their optimum positions, i.e. the L screw is set to seat the FD closeset to the seat tube.

i might have a look at the idea about removing one of the shims, although i'd probably be better off just spending the extra few quid on a new FD incase of any issues up the road, i really want everything to be as bomb proof as possible.

regarding the handlebars, they aren't cheap. they are the bars that Koga uses on their touring range.
i bought them at www.wallbike.com. i think they are the ITM Selego model

Quote:
Originally Posted by velo2000
I assume you've tried adjusting the low limit screw? Sheldon Brown has a good write-up here: http://www.sheldonbrown.com/derailer-adjustment.html. Maybe you can adjust it so you get no rubbing in the lowest gear (which you'll likely use on tour) but you will have some rubbing in the highest gear (which you're less likely to use)?

You're bike looks a lot like the one I'm building up. That's an interesting looking handlebar bag, care to elaborate on it? How is it mounted?
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Old 05-02-07, 06:54 AM   #5
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bb spindle too short?
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Old 05-02-07, 07:53 AM   #6
Collie
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probably... what's the solution? a new bb???
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bb spindle too short?
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Old 05-02-07, 09:52 AM   #7
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It does make one wonder whether your BB width is correct. I've never personally owned a frame where the gears were so close that a shim's width threw everything out. Doesn't that mean that the gears wouldn't fit if you had the "proper" width of seat tube. Sounds like the crank spindle is too short or the frame is screwed up, which considering the source is not likely.

Just to neaten things up, I've heard of people buying the 28.6 clamp for a retrofit, though I'm no sure who would sell that.
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Old 05-02-07, 10:31 AM   #8
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I asked Thorn before the purchase whether or not the Sugino xd600 crank would fit the BB intsalled on the Sherpa frame-set, but they said that they couldn't confirm it. So i took the chance and got the crank anyway.
so it sounds like that is the problem. i think there is a 3mm difference in the BB's. i assumed that 3mm would be insignificant, but it looks like i was wrong.

i'm not too worried for the moment, but it'd be nice to tune up the bike to it's optimum before the big tour

: )

Collie

Quote:
Originally Posted by Peterpan1
It does make one wonder whether your BB width is correct. I've never personally owned a frame where the gears were so close that a shim's width threw everything out. Doesn't that mean that the gears wouldn't fit if you had the "proper" width of seat tube. Sounds like the crank spindle is too short or the frame is screwed up, which considering the source is not likely.

Just to neaten things up, I've heard of people buying the 28.6 clamp for a retrofit, though I'm no sure who would sell that.
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