How to handle a tank slapper

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Valuable time? That's a joke. I can't imagine the hours you spend spewing
long winded posts of useless drivel, having nothing to do with origional
posts.

 

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Lol, Your all over the place, and make no sense.
Front tire slides, it rarely recovers, you get a "lowside"
Rear tire slides, often recovers, you get tossed. This is a "highside"

Your posts are full of this crap, and newbies listen to it.

 

Who the **** is Chad?

 

I have never highsided by loosing grip on the rear then regaining it...maybe
you are doing something wrong...

 

posts, even you observed that in a tank slapper, the rider's hands may
end up off the bars whether he wants them to or not. I think you even
said something about broken thumbs. Sometimes the wobble settles down
and sometimes it doesn't, but an attempt by the rider to hang onto the
bars does not usually have a productive outcome.

The OP was confused about what a speed wobble (tankslapper) and a speed
weave are. They are two completely different modes of oscillation. The
OP referred to seeing a video where the rider was thrown off his
machine, which recovered and crossed the finish line of the race track.
He thought that was a speed wobble. It wasn't, it was a high speed
weave...

I personally have been thrown off a few motorbikes by speed weave,
mostly in the dirt, once on asphalt, when I lost front tire traction.
In such a speed weave, the frequency of the handlebar movement is
nowhere near as fast as the frequency of the handlebar movement in a
true speed wobble...

The rider finds that he is able to hold onto the handlebars until his
feet get knocked off the footpegs by the amplitude of the rolling and
yawing motion. When his feet are off the pegs and his body is on one
side of the motorbike, it's time to let go, he will never bulldog that
steer, and he can't hang on with his weight flailing around alongside
the bike...

The rider then finds himself off to one side of the motorbike, rolling
like a log, and maybe his motorbike straightens up, maybe it doesn't.
If he puts his hands out to stop rolling, he will at least sprain his
wrists...

That's what happened to me as I log-rolled down a SoCal canyon,
alternately viewing the sky and the ground, sky and ground, and wishing
the motion would halt. My motorcycle wasn't badly hurt. It only cost
about $300 to fix it...

 

hotrodded? looks like a mostly stock late 90s R1100R with a aftermarket
muffler and a clipon windscreen. appears to have stock injection. The
catalytic convertor has been removed, thats more for weight reduction
rather than performance. It might have a Ohlins shock, I can't tell for
sure. Tires appear to be standard Metzeler MeZ4's. It has GS style
hand guards, those are great for keeping your mitts warm in colder
weather.

 

Well, oil coolers...

But yeah, those look bog standard.

 

OTOH, the convention of "Radiator" for H2O based coolant and "Oil
Cooler" for the engine oil is well established, as many liquid cooled
bikes have separate oil coolers.

 

Completely off-topic, but -- I have your card. Did I get it at
USENIX Security in DC in '03, or in Stockholm in '01?

 

DC in 03.

 

the oil coolers sticking out the side? those are totally stock R1100R.
there's no water cooling on a R bike.

here's a totally stock dealer loaner, from back in 2000

http://www.hogranch.com/CoolPix/30Jun00/DSCN6281-half.jpg
http://www.hogranch.com/CoolPix/30Jun00/DSCN6282-half.jpg
http://www.hogranch.com/CoolPix/30Jun00/DSCN6285-half.jpg

note the differences in the exhaust pipe. that was the ONLY thing that
was visibly non standard other than the windscreen and handgrips. stock
bike has a big pillow shaped cat under the tranny.

 

OK, I don't understand this. I thought that the wheel acted as a
gyroscope, and tended to keep moving in the same direction. What
really obvious freshman physics fact am I overlooking?

-Patti

 

Sure, there are gyroscopic effects associated with both front and rear
wheels, especially if they are spinning rapidly and the tire contact
patches aren't touching the ground...

Moto-X free-stylers have been showing off for decades now, with their
crossed-up jumps and rotating the chassis about its center of gravity
by increasing engine RPM with the throttle or by stepping on the rear
brake pedal while the bike is off the ground and free to behave as two
gyroscopes attached to a frame...

There's a three-finger rule to demonstrate what a gyroscope's rotor
will do if it is free to precess, but, of course, a motorcycle's wheel
isn't free to precess if the tire contact patch is touching the
pavement. That's why we go to all the trouble of employing complicated
high-$$$ suspension systems and strive to keep our tires in contact
with the pavement by careful throttle control on rough pavement...

Here's the three-finger rule as it applies to motorcycles and bicycles.
(Do not attempt to use three fingers arranged in this manner upon your
consenting partner, unless he or she is a large bovine or has been
fisted a lot...)

Hold your right thumb up and tilted at about 25 degrees to the
vertical, back toward you (precession vector and steering axis), point
your index finger away from you, and it will point a little upward
(torque vector and axis), point your middle finger to the left (spin
vector and axis). Imagine that the axis of wheel rotation is your
middle finger, and that the steering axis is your thumb...

Using your left index finger, push your right index finger so your
whole hand has to turn to the left, pivoting around the wrist. You'll
see that your wrist (symbolizing the steering head) has to bend to the
left, but it *twists* to the right...

That's a pretty good model of a motorcycle's steering system when the
front wheel is off the pavement, or just dancing lightly on the surface
and gets disturbed off to one side...

When the front tire contact patch is lightly dancing on the pavement,
the motorbike is about to wobble, and it's weaving all the time
anyway...

When the front tire contact patch is in good contact, it is providing a
restoring force that straightens the steering head up again. When it's
dancing, there's less restoring force...

What's that old song? It goes like: the steering head bone is connected
to the chassis bone and the chassis bone is connected to the swing arm
bone and the swing arm bone is connected to the rear wheel bone and the
rear wheel bone gets its act together, at least for an instant...

When you start out from a dead stop, the rear wheel will fall over to
the right or the left, but the thrusting of the front tire's contact
patch immediately stabilizes the machine's forward motion into a slow
speed weave, where the front tire's path can be seen to weave back and
forth across the rear tire's path if you ride through a puddle of water
onto dry pavement and then examine the evidence...

Almost anybody can hold a bicycle upright and stationary by applying
appropriate forces to the handlebars. When the bicycle is in motion,
the trail (or castor effect) in the front tire automatically provides
thrusts that push the chassis and the rear wheel back into an upright
position after the rear wheel tries to go off in whatever direction the
chassis happens to be leaning at the moment...

And the chassis is *always* leaning one way or the other, you can
*feel* it as a rhythmic motion around all three axes. If you're riding
a bike with a front tire that doesn't feel like it's "planted" firmly
on the pavement, the motion will tend to make you feel a bit uncertain
about the bike's handling, the machine will tend to wobble and weave
more than a stable-feeling motorcycle that doesn't make the rider
nervous...

Back in the 1960's, when motorcycles had big 19-inch wheels on the
front and had flexi-flyer steel tube frames, Triumph solved the
wobbling and weaving problems with "Daytona geometry". Their race bike
had 32 degrees of rake (!) in the front end, gawdawful large amounts of
trail, and the steering motion from side to side was limited to only
about 15 degrees before the steering would hit the stops. Triumph hoped
to keep their riders from being spit over the handlebars in speed
wobbles and speed weaves...

They had terrible hard rubber tires in those days, high-hysteresis
rubber that damped out wobbles and weaves was only just being invented.
There wasn't much weight on the front tire contact patch, it was mostly
on the rear tire, in order to get good traction for acceleration, and
road racing was mostly a drag race between corners, the riders would
pray that their brakes would stop them, and then they would tippy-toe
through the corners like a little old grandma on a moped...

Nowadays, modern sportbikes run from 23 to 26 degrees of rake and they
have a lot more weight on the front tire contact patch to keep the
much-improved front tire planted on the pavement, stabilizing the
machine...

 

Thanks for an absolutely wonderful explanation! I'm sure I'm not
the only person who appreciates your detailed descriptions.

-Patti

 

Ditto. I saved it to read again as I just got finished with
Schrodinger's Kittens and I'm still a bit muddled.