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  1. #1
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    Seat stays, bending and rear triangle flex.

    Hey Everyone,

    So, I just bought a tubing roller and used it to bend some seat stays on my last build. I really enjoyed the process of fabing the stays from scratch and I think I might like to do it from now on.

    It got me to thinking about how stay construction might affect the way a frame rides. I've seen things like Dave Kirk's terraplane stays, which are claimed to make a big difference in the frame feel.

    Anyway, I guess the best way to ask this is just, does anyone have any experience trying out different stays, and how did that work out for you?
    I've got some ideas that I'd like to try but thought I'd see what else is out there.

    Thanks!
    Adam

  2. #2
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    If you're just talking seatstays, it makes zero difference as far as I've ever been able to tell. S-bend, single bend, no bend, 14mm, 16mm, 19mm... they all feel pretty much identical to me. Chainstays can make a fairly big (subjective) difference.

    I have zero hard data to back up this position.

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  3. #3
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    Recently modified a frame for a customer - swapping straight stays with a wishbone for quite curvy double-taper 10-14-10mm stays. Customer reckoned it was noticeably softer to ride.

    Hetchins always claimed their curvy stays helped with comfort.

  4. #4
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    touring bike with s bends super flexy, straight guage 1 bend rides like on rails.
    single anecdote but different chainstays and tubeset, but I wont do s bends when it comes to wanting stiffness.
    cheers andy

  5. #5
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    I have to say, if N=1, the info is not that useful. Which also makes my post not useful, I guess - only way to find out is to try out some different stuff and ride, ride, ride!

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  6. #6
    saddlemeat
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    Garro. The ass doesn't lie.
    A Useful Bear is a handy thing.

  7. #7
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    ^^Walt, agree on the anecdote N=1,
    I do like the swoopy bends how they look, most folks aren't touring either.
    Make what you like This stuff is fun!
    cheers
    andy

  8. #8
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    Cool, well thanks for the thoughts guys!

    Sounds like everyone agrees just about as much as they do on chainstay bridges haha.

    I guess I'll just do some experimentation, or at least some marketing.

    Adam

  9. #9
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    Anybody interested in quantifying seatstay flex? I have access to tensile test frames that can provide load vs deflection data. I've wanted to do this for a while but I have no time to build test samples. If someone wanted to build a couple rear triangles that were identical accept for seatstays I would be happy to test them for vertical compliance.

  10. #10
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    That could be really interesting.

  11. #11
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    If someone will come volunteer to keep my 18 month old out of the dog food for a few hours, I'm all over it.

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  12. #12
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    Walt, that is an easy one. Just give the kid a bunch of cat food and they will be occupied.

  13. #13
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    Build a cage for baby first, then the frames.

    Problem solved.

  14. #14
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    These are all good ideas. Of course, dog food is the healthiest thing he will eat right now (tonight's meal: plain tortilla and some pickles) so maybe I should just let him do his thing...

    -W
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  15. #15
    Hi.
    Reputation: jtmartino's Avatar
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    Quote Originally Posted by adarn View Post
    That could be really interesting.
    Let me save you the trouble. As Walt has already mentioned in another thread, most hardtail frames don't exhibit any noticeable vertical compliance. The rear triangle would have to be so flexy that you run the risk of substantial lateral movement (which is a much bigger issue.) Build a triangle out of any material you want and try to touch the corners together by allowing the hypotenuse to bend inward. Not gonna happen, because it requires that the system flexes at multiple different points.

    While different frame materials may exhibit different vibration damping characteristics (making the ride feel harsher or smoother), your standard hardtail won't flex enough for you to notice that the wheel is traveling vertically. You'll get all your comfort from wheel/tire selection and seatpost/saddle selection. FWIW, I've ridden probably 15 different hardtails over the years and I've never actually felt anything resembling vertical compliance like I would on a softail.

  16. #16
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    Quote Originally Posted by bsieb View Post
    Garro. The ass doesn't lie.
    Stays can flex.
    But, you have to make it do it.
    Ask Steve Potts or Mike Ausberger.
    - Steve Garro, Coconino Cycles.
    steve garro el jefe/el solo. coconino cycles www.coconinocycles.com www.coconinocycles.blogspot.com

  17. #17
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    My mongoose hill topper has been hit 3 times hard enough to bend the chainstays. I managed to realign the frame while on tour. The little crimp on the crank side makes this difficult and I can see no reason for it. My crank is close enough that the inner ring overlaps the bottom bracket and there is plenty of clearance. Given the ease of bending the chainstays back there must be some side ways flex with a touring load. This is fatiguing requiring constant steering correction. There is also too much flex at the brake bosses and I would prefer a wishbone stay though it would be nice if these were made double butted. hit_and_run | Flickr - Photo Sharing!
    "Dish is illogical." Spoke of Vulcan.

  18. #18
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    Update

    So,

    I built a new frame and I put some inward bends into the seat stays, which earlier I had though might yield more compliance or whatever. I don't have to sit on it though, or even have it built up to realize that it is going to ride exactly the same as any other frame.

    This one is for a friend, but I'm going to experiment with a bunch of things on my next one though, including some really skinny stays. Not necessarily to achieve a flex, but more to see if I can break something.

    -Adam

  19. #19
    650b me
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    Adam, what tube roller did you buy, and what are you using for seatstay stock?

  20. #20
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    I got a harbor freight roller to do the big radius and I do clearance bends with this bender that I made - super janky, but I get surprisingly good results:

    And I've been using 5/8" x .035 for the stays.

  21. #21
    WIGGLER
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    I like it cool home grown toolin and the ORANGE Vans can only help!!!
    PAYASO 36er.....Live the Circus

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