actionbent part2

Discussion in 'Recumbent bicycles' started by Duram, Apr 14, 2006.

  1. Peter Clinch

    Peter Clinch Guest

    NYC XYZ wrote:

    > But you've got to check the gears, too, afterwards, to make sure
    > they're shifting right and all. I don't think they did too much of
    > this, though...he probably checked for half a minute!


    This is fair comment, but 30 seconds should be enough in the first
    instance, which still leaves us rather a lot of time. Tweaking the
    gears is easy enough with the adjuster screw where the gear cable
    goes into the rear mech, just needs the odd tweak to tune the shifting.

    > Now now, we all know about names and marketing...but I didn't know 80%
    > of effort expended in on behalf of air resistance!


    That is, IIRC, the approximate figure on a DF, though I can't
    remember if that's on the hoods, in a heavy tuck or what. But it
    does show approximately the degree to which speed is dominated by
    aerodynamics any time you get any sort of fast.

    > Still, my point is
    > that I should be at least as good as a DF, given my better aerodynamics
    > on the SMGT


    They're not /that/ much better. I have my seat reclined as far as
    possible and it's pretty clear that cycling with pals on DF leaned
    over the drops that the frontal area catching the wind isn't all
    that different. When they go into a full speed crouch it's quite
    obvious they have less frontal area than me.
    If you want better aero, that's what the Speedmachine is for (and
    to some extent, the Grasshopper).

    > Yes, I knew this going in, but I figured that I'd rather have more
    > puncture-proof or puncture-resistance than speed, if the penalty isn't
    > too large and way out of proportion.


    To put the dangers into perspective, I've had 2 punctures on mine
    in 5 years running standard Marathons. They give very good
    puncture resistance. The M+ is only really an issue if you're in
    Puncture Hell, otherwise they'd be standard issue rather than the
    plain Marathon.

    Pete.
    --
    Peter Clinch Medical Physics IT Officer
    Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
    Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
    net [email protected] http://www.dundee.ac.uk/~pjclinch/
     


  2. Peter Clinch wrote:
    > NYC XYZ wrote:


    [snip]

    > > Now now, we all know about names and marketing...but I didn't know 80%
    > > of effort expended in on behalf of air resistance!

    >
    > That is, IIRC, the approximate figure on a DF, though I can't
    > remember if that's on the hoods, in a heavy tuck or what. But it
    > does show approximately the degree to which speed is dominated by
    > aerodynamics any time you get any sort of fast.
    >
    > > Still, my point is
    > > that I should be at least as good as a DF, given my better aerodynamics
    > > on the SMGT

    >
    > They're not /that/ much better. I have my seat reclined as far as
    > possible and it's pretty clear that cycling with pals on DF leaned
    > over the drops that the frontal area catching the wind isn't all
    > that different. When they go into a full speed crouch it's quite
    > obvious they have less frontal area than me.
    > If you want better aero, that's what the Speedmachine is for (and
    > to some extent, the Grasshopper).


    [snip]

    Dear N & Peter,

    It's common to assume that recumbents have an aerodynamic advantage
    over the traditional diamond frame, but the advantage is actually
    limited to fairly extreme recumbents.

    You can see some of the surprising details on this speed calculator
    page:

    http://www.kreuzotter.de/english/espeed.htm

    Hovering the mouse over the radio button for the type of recumbent will
    pop up a picture that gives an idea of what a particular model looks
    like. After selecting a model, clicking on calculate at the bottom will
    give a predicted speed for the default values and the drag area used
    for the calculation.

    mph frontal type
    17.1 4.3433 recumbent long wheel base
    17.3 4.7889 df hands on tops
    18.5 3.3781 recumbent short wheel base
    19.4 3.2559 df hands on drops
    20.5 2.7111 df triathlon bars
    21.2 2.1748 recumbent short wheel base racer
    22.3 2.0397 df superman position
    23.1 1.5504 recumbent lowracer

    Obviously, these are idealized guides to what a particular bike and
    rider will do, with different tires and transmission efficiences
    affecting things. But for the same rider and power, it takes a
    recumbent that stresses speed instead of comfort to improve on the
    aerodynamics of an ordinary diamond frame:

    http://www.bicycleman.com/history/images/1933hour-record_lg.jpg

    Cheers,

    Carl Fogel
     
  3. Peter Clinch

    Peter Clinch Guest

    [email protected] wrote:

    > You can see some of the surprising details on this speed calculator
    > page:
    >
    > http://www.kreuzotter.de/english/espeed.htm


    Thanks for that link, Carl.

    > Hovering the mouse over the radio button for the type of recumbent will
    > pop up a picture that gives an idea of what a particular model looks
    > like.


    Note for this discussion that a Speedmachine would probably be somewhat
    better than the "ShortWheelBase, above seat steering, racing equipped"
    but not as good as "Lowracer, above seat steering". That assumes it's
    the ASS SpM rather than the new USS option.

    Pete.
    --
    Peter Clinch Medical Physics IT Officer
    Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
    Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
    net [email protected] http://www.dundee.ac.uk/~pjclinch/
     
  4. Jon  Meinecke

    Jon Meinecke Guest

    <[email protected]> wrote in message>
    > It's common to assume that recumbents have an aerodynamic advantage
    > over the traditional diamond frame, but the advantage is actually
    > limited to fairly extreme recumbents.
    >
    > You can see some of the surprising details on this speed calculator
    > page:
    >
    > http://www.kreuzotter.de/english/espeed.htm


    "It's not about the bike."

    You're correct that the differences are not as large as people
    might imagine. People who try a recumbent and think they will
    automatically be 10-20% faster *will be* disappointed. It depends
    on what you're comparing, but 3-7% without going"extreme"
    is quite possible, however.

    Note that the default tire choices on the kreuzotter website for
    non-race configured recumbents are medium and wide. The df
    tire choices are all high pressure, by default. Here's the list
    with the high-pressure tire choices for the LWB and SWB
    added**.

    mph frontal type
    17.1 4.3433 recumbent long wheel base (medium slick tires)
    17.3 4.7889 df hands on tops
    18.0 3.8777 recumbent long wheel base (high-pressure tires)**
    18.5 3.3781 recumbent short wheel base (wide slick tires)
    19.4 3.2559 df hands on drops
    19.5 2.8408 recumbent short wheel base (high pressure tires)**
    20.5 2.7111 df triathlon bars
    21.2 2.1748 recumbent short wheel base racer
    22.3 2.0397 df superman position
    23.1 1.5504 recumbent lowracer

    It's also worth noting that the two non-race configured recumbents
    modeled above are under seat steering. Most recumbent bikes in
    the US are above seat steering. The "recumbent short wheel base
    racer" may cover many of the so-called "high racer" recumbents
    (Bacchetta, Volae, RANS...) and these may not be considered
    "extreme" or sacrificing of comfort.

    Jon Meinecke
     
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