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Display Mesage #101900


Transitioning to the Dark Side - a Detailed Log
Written by daviddockstader on 4/2/2011 at 08:07 pm

We are not talking about the same thing. My statement was only about lean,
nothing else. I carefully specified that my statement applied to a given rider
position. Once the rider position is determined the motorcycle and rider can be
treated as if their entire mass were concentrated at the center of mass of the
system. If one imagines a line between the tire contact patches and then a line
perpendicular to this line through the center of mass, the only forces relevant
to lean are those acting on the center of mass that are perpendicular to this
line. All forces on the bike can be broken into forces perpendicular or parallel
to this line. Those parallel are balanced by the suspension, but those
perpendicular to the line must add to zero for the bike to be balanced. At this
point there are only two forces to consider: gravity and centripital.
Distribution of gravity forces are determined by the lean angle and the
centripital force is determined by the speed and radius of the curve. It is not
that tire forces are unimportant in cornering. They are obviously what makes the
bike turn, but for a given speed and a given radius for a given bike and rider,
those forces are fixed and any tire that makes the corner has to create those
forces. Force = mass X acceleration. For a given acceleration the required
force is what it is and changing tires won't change the equations.

Handling is another whole ball of wax. If your tires are distorting in an
unstable fashion and jumping around, then the driver has to go through all kinds
of contortions to compensate. Anyone who has hit a corner with a soft tire has
experienced this. As the tire jumps around both the lean angle and radius of the
turn jump around and the rider goes crazy. However, I don't think you can judge
any of this in a single still frame, other than to say that the rider looks
relaxed and riding in jeans and a T-shirt he looks pretty confident.

--- In ipcrc@yahoogroups.com, "literidr" <literidr@...> wrote:
>
> Sorry,
>
> The shape of the tire is a major factor in the ability of the tire to
negotiate a turn. When you are turning, the inside radius of the tire in
contact with the road is shorter than the outside radius of the tire, allowing
your tire to contribute to the steering ability of your bike. You can enhance
your bike's ability to steer by shifting your weight in the saddle, even
dragging a knee if you're that confident, but you have to start with the ability
of your tires to negotiate a curve and that means the shape of the tire.
Obviously, the rider in that picture was able to work with the bike to get
around the curves but as the pictures clearly showed as I looked at bikes before
him and after him (which would have limited how fast he was able to ride) he was
working harder to get the bike to do what he wanted. I've put over 200K on my
PC's now and I've been through the Dragon enough and seen pictures of me riding
through the dragon enough to know how it should handle and look. Your friend
was clearly having to work harder to get the same job done.
>
> John Handford, literidr@...
> Taylors, SC
> '90 PC "Spirit"
>
>
> --- In ipcrc@yahoogroups.com, "David" <david.dockstader@> wrote:
> >
> > I have to disagree. The lean angle for a give bike and rider position is
just a function of speed and radius of the turn. He was going fast! Anybody else
going that fast would also lean that far.
> >
> > --- In ipcrc@yahoogroups.com, "literidr" <literidr@> wrote:
> > >
> > > That photo in the Dragon is scariest of all. When you see how far over
that bike had to lean to make that curve compared to all the other bikes, you'll
realize that curves are not what those darkside tires are good at.
> > >
> > > John Handford, literidr@
> > > Taylors, SC
> > > 90 PC "Spirit"
> > >
> >
>

Message Thread for message #101900