>Please help me understand what causes a tank slapper to start.. ... What is
the correct procedure to stop one before it gets out of control.. ( increase
throttle....decrease throttle.... shift weight back.......) Are there
different causes of tank slappers?

***
This is my opinion. I'm not an expert in physics nor motorcycle geometry.
***

Different causes (20+ and counting) and sometimes different responses
but.....

Shimmies, speed wobbles and tank slappers are different levels of the same
problem: the bike's geometry is not interacting with the conditions present as
designed. Sounds vague, but there are MANY sources/conditions that can lead to
one of these and I can't name them all. When a bike's self-correcting steering
nature that allows one to ride hands-off (under controlled conditions of
course) overcorrects inducing a harmonic oscilation that builds in intensity
until the left-right-left motion is so fast/great that the bike looses
control.

This is why marching armies break up their marching to let each soldier march
their own pace on some bridges. Hundreds of feet coming down on a bridge
*LEFT-RIGHT-LEFT-RIGHT-LEFT...* can cause it to sway up and down. If each
group step of the army coincides with the down-flex of the bridge's waving,
the wave crests stack up and kinda amplify the forces, pushing the bridge to
flex farther and farther (like when you get going on a swing set) until the
bridge fails.

You could think of the bike in similar terms where the bike overshoots it's
corrective steer faster/greater building on each successive turn of the
handlebars til... well, the bridge fails and you're tossed in the drink.
Sometimes wind buffeting grabs and pulls on fairings, windshields, backrests
and saddlebags in a similar fashion.

Some causes and or contributing factors (sometimes a combinations of these),
but by no means all of them:

*Out-of-spec bearings (wheel, steering head, swing arm, ...)
--bearings too loose
--worn bearings
--improperly shimmed
--spun outer race
--improper alignment (deficiencies in the rear of the bike CAN be telegraphed
to the front)
-- etc. ...
*Out-of-spec wheels/tires
--out of true
--out of round
--improperly balanced
--improperly seated/inflated
--unusual wear pattern
-- etc. ...
*Poor suspension
--improperly adjusted
--overloaded
--worn/defective components
-- etc. ...
*Improperly loaded bike
--too much weight on the back and not enough on the front tire
-- etc. ...
*Bad steering dampener ...
*Wind turbulence (fast wind and or highway speed)
--handlebar mounted windshield, jacket or anything else the wind can catch
--exposed pillion back rest
--saddle bags, especially wide ones on naked bikes
--mis-aligned or damaged fairing
-- etc. ...
*Frame flex
--any change in the bike's geometry that induces an undesirable effect ...
*Road grooves
--any road characteristic that induces bike instability (not to be confused
with a bike's natural tendency to follow a groove or path of most traction)
-- etc. ...
*Anything else that can lead to or build on a harmonic oscillation affecting
the bike's steering which can also be a permutation and or combination of
factors that add up to a wobble...


Seems like a lot, right?

A properly maintained, loaded and accessorized bike ridden conservatively
under good riding conditions (weather/road) is least likely to experience a
wobble, but I won't say that it still can't happen.

How Do You Handle It?

According to the MSF (MRC:RSS Student Workbook page 41)
"... Keep a firm hold on the handlegrips but don't lock your arms and fight
them. Ease off the throttle as you move your weight down and forward.

"And don't believe the "old timers" who say to accelerate through a wobble. It
doesn't work.

"If you can't determine the cause (such as incorrect loading or improperly
adjusted suspension), take the motorcycle immediately to the dealership."

>... which might mean trailering it, you don't want to ride a questionable
bike.

Nothing is absolute (hey, there's a contradiction!) so I guess there is always
the chance that this might not work for certain bikes under certain conditions
due to certain causes .... but it should address the common ones. I've heard
that some folks have expreienced a wobble only at a specific speed on their
bike and can speed up to get out of a wobble zone. However, how can you be
sure you have that type of wobble and that acceleration won't worsen the
problem? Do you know how to tell the difference? I don't.

The way I figure it, you can never hit something too slow.

That does NOT mean to brake, especially not the front brake whose traction is
already grealty squandered, during a wobble.

Again, this is just my opinion and is no substitute for you going out and
doing your own research.

Please post this to the IBMWR list for me as I share it with the Airheads
list. Thanks.

-Joe ABC 3335, IBMWR, HoAME, MSF; '78 R80/7 "KRAUT"; KC BBQ
I will no longer be using 70cuda@usa.net as of 31 July '01.