Riding Position and Shimmy

Discussion in 'Cycling Equipment' started by Kennin, Oct 9, 2003.

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  1. Kennin

    Kennin Guest

    I've recently test rode 3 different road bikes down a fast, curving descent and experienced a shimmy
    as I approached 35 - 40 mph. Two of the bikes were titanium and one was steel. On my current
    aluminum frame, I take the same descent at 48+ mph and always feel in control. I did feel that I had
    a longer/lower reach to the bars on the demo bikes.

    How can I best determine a proper, well centered riding position? What are the more common frame
    geometry differences that may account for such a dramatic change in handling?

    Thanks, Ken
     
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  2. Jim Beam

    Jim Beam Guest

    > I've recently test rode 3 different road bikes down a fast, curving descent and experienced a
    > shimmy as I approached 35 - 40 mph. Two of the bikes were titanium and one was steel. On my
    > current aluminum frame, I take the same descent at 48+ mph and always feel in control.

    what make is the aluminum frame? what diameter tubes does it have? what size is it?

    jb
     
  3. Shimmy is apparently a part of the intrinsic geometry of some bikes. If you shift your centre of
    gravity you can stop it. Read Jobst Brandt on it in the cycling FAQ
     
  4. Jobst Brandt

    Jobst Brandt Guest

    Garry Lee writes:

    > Shimmy is apparently a part of the intrinsic geometry of some bikes. If you shift your centre of
    > gravity you can stop it.

    I think I dispelled that in a number of tests (riding no-hands) leaning back leaning forward and
    making no change in the shimmy that occurs naturally with my bicycle if I allow it to do so. Tests
    were also done with balanced and unbalanced wheels as well as one filled entirely full with water to
    see what rotating mass had to do with it. These all had no effect on initiation of shimmy.

    > Read Jobst Brandt on it in the cycling FAQ

    http://draco.acs.uci.edu/rbfaq/FAQ/8h.5.html

    Jobst Brandt [email protected]
     
  5. Kennin

    Kennin Guest

    jim beam <[email protected]> wrote in message news:<%[email protected]>...
    > > I've recently test rode 3 different road bikes down a fast, curving descent and experienced a
    > > shimmy as I approached 35 - 40 mph. Two of the bikes were titanium and one was steel. On my
    > > current aluminum frame, I take the same descent at 48+ mph and always feel in control.
    >
    > what make is the aluminum frame? what diameter tubes does it have? what size is it?
    >
    > jb

    My aluminum bike is a GT ZR4.0 - 52cm. Tubes are oversized with rather unique
    shapes...relatively stiff. The Litespeed Siena was a Med.(53) and the Litespeed Vortex was a
    55cm. I felt better situated on the GT, and wonder if I'll get as comfortable once I dial in
    position on a Litespeed. Thanks.
     
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