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Old 01-21-07, 10:12 PM   #1
TallRider
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using a flat bar with old 25.4mm-clamp road quill stem

In converting my Schwinn Le Tour increasingly more for commuting purposes, I'm going to use a flat bar and use 7-speed Shimano rapidfire brake/shift levers pulled from an old mountain bike.
Thing is, the Schwinn is one of those old ones that has a narrower internal head tube diameter requiring a narrower (21.15mm) quill stem. So I'm using an old Schwinn-specific SR forged quill stem, pictured here. The clamp diameter is correct - 25.4mm - but these old road quill stems don't have as wide of a clamp and may not support the bar as well when it is torqued side-to-side.
Any thoughts on this issue? I have no experience here, and don't expect for there to be a problem, but wanted to know if there's any reason this would be more flexy, or more likely to crack a lightweight aluminum bar.
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Old 01-22-07, 01:45 AM   #2
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Wouldn't a 7 speed mountain bike likely have 26mm bars(assuming your bars are also from the bike you scavenged the shifters from)? If they are indeed 25.4mm then try it, as long as they are not already damaged.
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Old 01-22-07, 03:23 AM   #3
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Absolutley nothing wrong with it. The road stem will give you a low stance though. Why spend more money on new bars and stem when you've already got the parts.

Tim
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Old 01-22-07, 06:56 AM   #4
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Quote:
Originally Posted by Moose
Wouldn't a 7 speed mountain bike likely have 26mm bars(assuming your bars are also from the bike you scavenged the shifters from)? If they are indeed 25.4mm then try it, as long as they are not already damaged.
All mountain bike bars are 25.4mm clamp diameter, except for the new oversize standard that's 31.8, but that's only come around in the last 5 years I think and still isn't the most common.

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Absolutley nothing wrong with it. The road stem will give you a low stance though. Why spend more money on new bars and stem when you've already got the parts.
Thanks for the vote of confidence.
It actually won't give a low stance, at least not compared to running road bars on the same stem, because with the flat bar my hands are only as far forward (albeit wider apart) than when they're on the bar tops. The brake hoods and the drops are both further away than the bar tops.
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Old 01-22-07, 07:18 AM   #5
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Also, here's some pictures of what I'm talking about. There is a slight gap on the edge of the top of the clamp, although otherwise the fit is fine and the clamp size is correct.



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Old 01-22-07, 07:27 AM   #6
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I am not a physicist or engineer, but I think that you are fine.

I would think that most of the stress on a handlebar is related to the distance betwen the edge of the clamp and the end of the bar (leverage), and not necessarily the lampp width (within reason). You would have an effective length difference of a couple of MM on each side, and I would hope that the tolerances on the bar can handle that... If they can't then I wwould consider it a design probelm with the bar.

There may be factors I don't know enough to consider, but if it were my bike and bar I wouldn't worry about it.
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Old 01-22-07, 08:36 AM   #7
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I think you're right that I'll be fine, especially since I'm using this on a road commuting bike, so I'll be torquing on the bars a whole lot less than would be the case if I were riding trails on a mountain bike - and the bar is designed for trails.
But your physics is wrong. The stress on the handlebar at the clamp area, caused by the clamp stabilizing the bar while the rider is torquing on it, gets larger as the ratio between (distance of rider's hands from bar center)/(distance from bar center to edge of clamp). It's just a ratio of torque. So a wider clamp area would diminish the amount of stress on the bar at the edges of the clamp.
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Old 01-22-07, 08:48 AM   #8
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It isn't even 10:00 am yet, and I have learned something. My day is a success!

I thought that a ridiculously narrow clamp would be a potential issue (intuitively) but couldn't come up with a reason that it would be the case. Now I see it.

Thanks for the info!
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Old 01-22-07, 09:25 AM   #9
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I studied engineering and physics for my first two years in college before I started studying people.
The clamp on the SR stem is narrower than typical bolt-on-faceplate modern mtb (and road) stems, but it's not ridiculously narrow - I noticed that the logos on the handlebar would be partially covered up if the stem's clamp were any wider.
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Old 01-22-07, 12:47 PM   #10
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I've got exactly that setup - 25.4 clamp quill stem onto a cheapie flat bar - on my fixie and it works great. Bar isn't even cut down and I haul on it when I'm grinding up a hill (48/16) wih no problems. I think you're golden.
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Old 01-22-07, 01:41 PM   #11
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Originally Posted by tellyho
I've got exactly that setup - 25.4 clamp quill stem onto a cheapie flat bar - on my fixie and it works great. Bar isn't even cut down and I haul on it when I'm grinding up a hill (48/16) wih no problems. I think you're golden.
Great to hear, thanks. You'll torque on it more on your fixie than I will with a 40t single chainring and 13-32 7-speed cassette.
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Old 01-22-07, 07:28 PM   #12
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Forte bars don't tend to be ultra-light-weight cutting edge high performance bars and should be able withstand whatever abuse you give them.
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