Timberwoof wrote:
> "mentALEXcersize" <(E-Mail Removed)> wrote:
> > I have found that lighter, unloaded sportbikes with fatter tires (larger
> > contact patch) laugh at many extremely windy conditions.
> I'm curious.
I've noticed that ;-) ;-)
> Why would the size of a bike's contact patch make a difference? It
> seems to me that it would be all about the frontal area presented to
> the wind, the bike's mass, and the location of the center of drag.
The size of the rear tire's contact patch and its profile makes a lot
of difference in a motorbike's resistance to being blown around by the
wind.
A bigger contact patch has more *grip*, and that grip isn't necessarily
related to the classic coefficient of friction that most of us studied
in high school or college physics classes. Weight does matter, and area
of the contact patch matters too, but synthetic rubber tires *adhere*
to the pavement and soft rubber interlocks with the surface roughness
to grip the road. Classic studies of coefficient of friction do not
address adhesion at the molecular level, it's never considered that
anything may be transfered beween the two saurfaces, nor is in
considered that the surfaces may interlock...
So far as aerodynamics are concerned, a motorbike (with a big fairing
up front and the center of pressure far forward and the combined center
of gravity rather far to the rear, especially with the rider sitting
upright) is aerodynamically unstable...
An arrow or a weather vane automatically turns into the wind and aligns
with the wind. A faired motorcycle with tend to turn away from the wind
because of all that area up front. However, the front tire will
automatically compensate for the motorbike being pushed off the
intended course. If you have a steady wind from the side, a motorbike
will automatically lean into the wind slightly. But there is always a
problem of
traction balance between the smaller front tire and the larger rear
tire. The smaller front tire has to work harder to keep the bike going
straight when there is a side wind, and the amount of automatic
correction it makes may not be enough, the rider may have to
countersteer a bit to make the motorbike lean a little more, or he may
decide to shift his weight toward the windy side...
Decades ago, it was popular to replace the stock Bridgestone Cyrox
radial 140mm wide rear tires on GSXR-750's with Dunlop K-591 170mm wide
tires.
Those tires were 1.18 inches wider than stock and they would have too
much profile when they were new. Gusts of wind on the flats in the
Antelope Valley would easily blow my GSXR all over the road. But, as
the tire profile wore off and it became flatter in the middle and rear
traction would increase because the tire contact patch was getting
bigger.
The rear tire felt rock solid in a cross wind, but the front tire had a
much harder time compensating for the wind. I had to put a lot of
pressure on the handlebars to countersteer...
After years of using those K-591's, Dunlop discontinued them and I
decided to try some 140mm wide Bridgestone BattleAx BT-45V's. I figured
that th GSXR would be more agile in the tight canyons. It was, but
gusting winds would blow the GSXR across the road...
> I found that my big heavy R1100GS, although it's taller, deals with the wind
> better than my little CB-1 did.
As above. Weight, tire contact patch size, tire profile...
|