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  1. #1
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    Does a brake bridge add strength?

    I'm nearing completion of my Bamboo Bike frame build and was wondering if I need to install the included brake bridge that came with the kit? I will be running disc brakes front & rear so it's not needed for brake mount. Could use it for a fender mount...but a lighter duty cross piece can be easily added.
    Does a strong brake bridge improve the overall frame performance any?

    Thanks.

  2. #2
    Randomhead
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    There are many steel frames without brake bridges. This is the kind of discussion that engenders a lot of heat and not much light for some reason.

    My opinion is this: of all the tubes on a bike, the seat stays are the most fragile. If you aren't mounting a brake on the bridge, you probably don't need a heavy duty bridge. I think it might make sense to have a bridge just to limit the damage from the occasional handling force that bikes go through when they aren't being ridden. As far as forces on a bike that is being ridden, they really don't add much.

  3. #3
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    While I don't doubt that a brake bridge adds strength, I don't think that it is needed strength. It's more important that you add a brace across the brake side stays to support the disc braking forces.

  4. #4
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    Quote Originally Posted by Canaboo View Post
    While I don't doubt that a brake bridge adds strength, I don't think that it is needed strength. It's more important that you add a brace across the brake side stays to support the disc braking forces.
    I need the adpator fitting to mount my disc caliper to the dropout...it that what you are referring to?
    Here is what my rear dropout has for disc brake caliper mounting:

    148426952.iaOh8o0N.jpg

  5. #5
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    No, I mean the standard strut that almost all disc specific frames have that spans the SS/CS diagonally across roughly where the carbon ends on the bamboo.
    Like so:
    http://4.bp.blogspot.com/-Lp3Grb99r6...ke%2Bmount.jpg

  6. #6
    Andrew R Stewart Andrew R Stewart's Avatar
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    The drop out with disk mounts attachment to the stays looks under engineered to my eyes. As it is currently, IMO, it will tend to rotate around the axle, without much bracing between the disk mounts (upper) and the seat stay It would not surrprise me if the drop out works loose of the stay ends. Only if the disk mounts were attached futher up the seat stay would a brace from the seat stay to the chain stay help. And then that would be a very good addition. Andy.

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    Quote Originally Posted by Andrew R Stewart View Post
    The drop out with disk mounts attachment to the stays looks under engineered to my eyes. As it is currently, IMO, it will tend to rotate around the axle, without much bracing between the disk mounts (upper) and the seat stay It would not surrprise me if the drop out works loose of the stay ends. Only if the disk mounts were attached futher up the seat stay would a brace from the seat stay to the chain stay help. And then that would be a very good addition. Andy.
    I agree that the tab "floating" out past the ss greatly reduces how effective the strut will actually be. Short of using a better dropout design though, it seems like tying the two stays together can't hurt.
    The BBS dropouts feature large "teeth" that sit outside a slot in the bamboo with the carbon wrapping encasing it and wound between the teeth.
    That part seems grossly over-engineered from a strength standpoint. I think that the butt joints between the balsa and stays has more potential to be the weak link.

  8. #8
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    Like most things in life, the proof is in the pudding. We'll see how the design holds up...BBS has claims on their site that their frame build technique has hundreds of builds that have held up for years now...bike couriers in NYC report them lasting over 3 years in constant use. Though the disc brake setup is likely a recently added option for them, I suspect it's tested well for them.


    Quote Originally Posted by Canaboo View Post
    I agree that the tab "floating" out past the ss greatly reduces how effective the strut will actually be. Short of using a better dropout design though, it seems like tying the two stays together can't hurt.
    The BBS dropouts feature large "teeth" that sit outside a slot in the bamboo with the carbon wrapping encasing it and wound between the teeth.
    That part seems grossly over-engineered from a strength standpoint. I think that the butt joints between the balsa and stays has more potential to be the weak link.

  9. #9
    Randomhead
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    it's pretty hard to put years of use on a design like this. Steel framebuilders put that brace in after a large number of frame failures due to braking forces. Hard to imagine that bamboo holds up better.

  10. #10
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    Quote Originally Posted by unterhausen View Post
    it's pretty hard to put years of use on a design like this. Steel framebuilders put that brace in after a large number of frame failures due to braking forces. Hard to imagine that bamboo holds up better.
    I believe that the typical failure point in a steel frame tends to be in an area where it's actually the carbon lug of a bamboo bike that would be taking the brunt of the force.
    I recently took a broadside from a car that struck my rear wheel with sufficient force to destroy it but left my frame unscathed.
    It seems to depend on the bamboo type when you compare it to other frame materials.

    James Wolf actually used to make the disc specific frames for Boo without the brace and had failures. Not sure exactly where the failure point was though.

    I do know that testing shows that the butt joints of the BBS builds have been demonstrated to be the weak point, which is not really surprising.

  11. #11
    Andrew R Stewart Andrew R Stewart's Avatar
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    I've been waiting for the bamboo bike thing to mature. Part of that is the weeding out of designs and methods that are not up to snuff. The steel bike we all know and copy has had how many (enter a really big number here) come before what you make/buy today. Kind of like natural selection. The bamboo bike business hasn't even scratched that surface yet. But it is taken to heart and held as the new, and therefore better, thing. Andy.

  12. #12
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    Quote Originally Posted by Andrew R Stewart View Post
    I've been waiting for the bamboo bike thing to mature. Part of that is the weeding out of designs and methods that are not up to snuff. The steel bike we all know and copy has had how many (enter a really big number here) come before what you make/buy today. Kind of like natural selection. The bamboo bike business hasn't even scratched that surface yet. But it is taken to heart and held as the new, and therefore better, thing. Andy.
    True, but the current bamboo revival has the benefit of all the knowledge we now have of the properties of various materials and how they are best joined together.
    All the wood and composite based airplanes that were built years ago and continue to be built today has a trickle down effect on the keys to good construction technique.
    The access to adhesives and fibers that have proven themselves in high stress situations while bonding dissimilar materials is a big help to boosting the learning curve.

  13. #13
    Andrew R Stewart Andrew R Stewart's Avatar
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    Canaboo- Perhaps to the joinery there is a history but my comments were motivated by the design elements of TornadoCan99's disk drop out. Even if the frame was built of steel i'd feel the same. Like I said this material, bamboo, is in it's early days. It reminds me of the early Alu, Ti or carbon fiber frames which closely mimicked steel designs. It took a number of years before manufactures evolved the designs and joinery to best use the nature of the new materials. Andy.

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