[image: View Post]Bruckner, on Oct 26 2007, 09:52 AM, said:
Basic question you'll say but here, lately I found that the bike was less than rock solid at highway speeds in curves, I feel a bit of a wobble, could be due to lower temperature tire operation (low 40Fs), but then I looked at the rear tire closely (never done that before!) and found that the center section was considerably more worn than the sides (obviously?), when I run a finger over the tire I feel the edges on either sides, but this could be entirely normal.
Gosh I'm uneducated..
Regards,
Bruckner
If your problem is with the rear then is should feel more like a weave than a wobble...
to understand the difference between a WEAVE AND WOBBLE read on...
Most of us have experienced a wobble or a weave or have been told
about them. Few of us have a clear understanding of what a wobble
or weave actually is. Motorcycle instabilities are usually lumped
into a catch-all description wobble. Before one can do anything about
a problem, one must first understand its nature. There are three
destabilizing forces acting on a motorcycle as it moves down the
road: weave, wobble and upset. When a bike weaves enough to notice,
the front fork assembly remains straight and the rest of the motorcycle
moves from side to side several times each second. A bike that is
seriously wobbling shakes its head while the rest of the machine remains
mostly straight and stable; the shaking (wobble) is very rapid and
difficult to control. Upset simply describes the same tendency to fall
over as the machine has when it is stopped.
When interpreting the dynamics of motorcycle stability, it is useful
to view a motorcycle as having two major dynamic assemblies: the chassis
aft of the steering head and the front fork assembly. Like the wheels
of a shopping cart, these assemblies can sometimes embarrass us.
Any motorcycle chassis constantly tries to oscillate (weave) back and forth
about the steering head at between two and five times per second. Every
bike has this instability; it is held in check by damping forces created
mainly by the rear tire's self-correcting tendencies. If the tire's
natural oscillation frequency happens to coincide with the chassis,
the bike will weave. This seldom happens,though, as tires have much higher
frequencies than the typical chassis. For the tire to do its work, it must be
properly inflated and rigidly connected to the chassis. Worn swingarm
bushings, or poorly damped suspension springs can defeat the best tire's
stabilizing influence.
CUPPING:
Cupping, which is more accurately described as scalloping is a natural
wear pattern on motorcycle tires and it will always follow the tread
pattern. It is not a sign that you have bad suspension parts. It
merely shows that your tire is indeed gripping the road when you make
turns (thank you for that Mr. Tire!). This cupping develops within the
side wear bands of a leaned motorcycle. The extreme forces that come
in to play when the bike is leaned in a turn are what produce the
effect and when the wear becomes sufficient, one will experience
vibration and noise when one banks into a turn. Cupping follows the
tread pattern. The leading edge of the tread does not flex much as it
grips the road and the rubber is scuffed off the tire in that area
causing a depression. As the tire rotates, the pressure moves to the
trailing edge of the tread pattern where the tread flexes more causing
less scuffing so less material is ground off the tire. The more
complex the tread pattern, the more complex the cupping pattern will
be. The softer the compound of the tire, the sooner this cupping will
develop. Radial tires are more prone to cupping than are bias ply
because the compound of radials is softer. Low tire pressure will
exacerbate this wear pattern and you will lose many serviceable miles
by running low. Improper balance has nothing to do with cupping on a
motorcycle tire. Improper balance will merely cause your bike to
vibrate within certain specific speed ranges.