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Mixte Frame Question

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Mixte Frame Question

Old 11-10-21, 12:45 PM
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Tandem Tom
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Mixte Frame Question

As I start to ramp up to build a mixte for my wife I thought I would tap you fellows for a bit of info.
My question today is the "diagonal" tubes that run from the HT to the rear dropout. I looked at a number of pics of mixte frames and for the most part they run straight back but some "curve" abit. So as I look at her current mixte I would like a long HT this would seem to change that "straight line" of the twin tubes going back to the rear dropout. Am I looking at a potential problem by considering a bit of a curve?
Thanks!
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Old 11-10-21, 01:50 PM
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unterhausen
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I think the standard straight tubed mixte has a fairly high stepover, so curving the tubes seems like a good idea. Particularly if the curve is relatively short and near the seat tube connection.

Make sure the chain clears the diagonal tube before you get the frame painted. Don't ask me how I know
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Old 11-10-21, 03:00 PM
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Thanks!
As I get further along in the process I will post some drawing ideas.
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Old 11-10-21, 05:16 PM
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I'm not a framebuilder, but I am a mixte fan and I like the look and the lower stepover of the curved diagonal tube. unterhausen brings up a great point. I have noticed that when a frame has a curved diagonal tube, it sometimes terminates at the drop out, as with a straight diagonal, and sometimes it ends intersecting the seat tube, above the dropout. I think that with perhaps more bend that the diagonal is lower where it passes the chain and this upper landing point assures that there will be no rubbing. It looks good too with the deeper bend.

This frame from Muse Cycles demonstrates that deeper bend intersecting with the seat tube above the drop out.

Muse Cycles Mixte
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Old 11-10-21, 05:17 PM
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I believe the French refer to this style as "Berceau" which translates to "cradle."

Allow me to provide a little inspiration for your project:





Brent
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Old 11-10-21, 05:42 PM
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unterhausen
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That diagonal stay on the Folly would need to have a big dent in it for the chain if using a modern drivetrain. Rene Herse makes a modern derailleur for it though.

Seems like that suicide lever fd earns it's name on the mixte even more than it would on a diamond frame bike.
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Old 11-10-21, 07:29 PM
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Wow!
I guess I am not off track with my idea!
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Old 11-14-21, 02:57 AM
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Sven Cycles in the UK build a Berceau-style mixte like the Follis. It gives a lower step-over than if the stays were straight, right enough, and I guess the way they're curved twice enables them to attach to the seat tube higher up than if they just had one curve, if you see what I mean, and the higher up they attach, the stiffer / less noodly the frame will be. I think it's the most elegant solution of the lot, although it only gives a slightly lower step-over than straight stays. The curves of the stays are more flowing on the Sven than the Follis, but me not being a framebuilder I wouldn't know how hard it would be to do - I guess you'd need two different tube benders/formers? Can't imagine it would be easy, though, so good luck!



It's hard to tell from that photo but I found another photo that shows how the stays don't go all the way to the dropouts, they attach to the seatstays with a long mitre.



I restored a Raleigh Wisp mixte for a neighbour a few years ago and although the stays were straight and went all the way to the dropouts, I remember now, from what unterhausen explained above, that the inside of the diagonal stay on the drive side was dented to clear the chain - I didn't notice it but someone else pointed it out. If I was a framebuilder I would totally have learned that the hard way!

https://www.svencycles.co.uk/the-roadster-step-through
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Old 11-14-21, 03:21 AM
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Originally Posted by Velo Mule View Post
I'm not a framebuilder, but I am a mixte fan and I like the look and the lower stepover of the curved diagonal tube. unterhausen brings up a great point. I have noticed that when a frame has a curved diagonal tube, it sometimes terminates at the drop out, as with a straight diagonal, and sometimes it ends intersecting the seat tube, above the dropout. I think that with perhaps more bend that the diagonal is lower where it passes the chain and this upper landing point assures that there will be no rubbing. It looks good too with the deeper bend.

This frame from Muse Cycles demonstrates that deeper bend intersecting with the seat tube above the drop out.

Muse Cycles Mixte
The stays on the Muse Cycles Mixte are reminiscent of those on the old Deutsche Post bikes, although that was one of the wackiest frame configurations you'll ever see (but wonderful!).

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Old 11-14-21, 04:33 AM
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Originally Posted by kylecycler View Post
Sven Cycles in the UK build a Berceau-style mixte like the Follis. It gives a lower step-over than if the stays were straight, right enough, and I guess the way they're curved twice enables them to attach to the seat tube higher up than if they just had one curve, if you see what I mean, and the higher up they attach, the stiffer / less noodly the frame will be. I think it's the most elegant solution of the lot, although it only gives a slightly lower step-over than straight stays. The curves of the stays are more flowing on the Sven than the Follis, but me not being a framebuilder I wouldn't know how hard it would be to do - I guess you'd need two different tube benders/formers? Can't imagine it would be easy, though, so good luck!
For a large radius bend, using a roller bender is probably required. Although I have seen people use a plywood form. The Follis could be done with something like a Diacro.

Dual diagonal frames are generally considered to be fairly noodly, no matter how they are routed. That's why higher performance step through bikes use a single top tube. If it were to be used for touring, that might matter. Otherwise, I can't imagine it would.

Originally Posted by kylecycler View Post
The stays on the Muse Cycles Mixte are reminiscent of those on the old Deutsche Post bikes, although that was one of the wackiest frame configurations you'll ever see (but wonderful!).
That Deutsche posit bike is pretty neat, a lot of stuff going on there. Probably would be electric nowadays.
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Old 11-14-21, 07:42 AM
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Regarding the curved bend. Had a thought the other day about how I might go about this. As a woodworker I had 2 ideas. First was 2 complementary forms with half the tube diameter routed in each form. Then using bar clamps to squeeze the forms together. The second was 1 form and a "following" pulley both routed make the bend. But like wooden pieces I have done I sure there will be spring back that would need to be accounted for.
My thought process is starting to gear up!
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Old 11-14-21, 02:03 PM
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Vees work fine for large diameter bends, and are not as sensitive to tubing diameter. For my fork bender die, I cut each half on the tablesaw set to 45 degrees. You could use a router.
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