I feel stupid for asking but.........

[BlackCatRider]

What's a tank slapper? I've scene this term used alot but can't figure out what it means. Sorry about the dumb question.

[woobie]

Normally a tank slapper happens when your front tire leave the ground and lands turned off to either side . The handle bars will shake back and forth as the bike tries to realign it self.

here's a vid

http://www.uponone.com/videos.php?id=40

[Bob]

i no longer like that term.....

[SweetLou]

Re: I feel stupid for asking but.........

What's a tank slapper? I've scene this term used alot but can't figure out what it means. Sorry about the dumb question.

Don't feel that it is a dumb question. We all have to learn somehow, and if youdon't know, the best way to learn is to ask!

Now, as for having to worry about tank slapping on the kat... sure, it could happen, but not very easy. I have landed a big arse wheelie, with the bars turned, and they straightened themselves out upon landing. I was very surpised. (And yes, I was in a safe, unpopulated place with ZERO traffic!)

[tzortn]

Re: I feel stupid for asking but.........

Don't feel that it is a dumb question. We all have to learn somehow, and if youdon't know, the best way to learn is to ask!

True, but the search function can also be very powerful. There is a lot of good info already posted to the site.

[Black_peter]

Normally a tank slapper happens when your front tire leave the ground and lands turned off to either side . The handle bars will shake back and forth as the bike tries to realign it self.

here's a vid
http://www.uponone.com/videos.php?id=40

Mine happened after sitting up in the seat after trying to see
how fast my bike could go.. I closed the throttle, sat up and
whoooooohhhhh shhhhiiiitttteee!!!

[The CyberPoet]

The tendency to tank-slap (induce such violent oscillations, also called head-shake) is a matter of the bike's design, specifically the wheel base length, the fork (rake/steering) angle, and the fork length. The closer you place the tire to directly under the steering head, the less stable it becomes (in linear terms) and the more likely you are to encounter increasing oscillations if something upsets the front end; in really bad designs, something as simple as a rut in the road can start one that can't be readily recovered from at speed.

Fortunately, the Katana is particularly stable in it's design, with a very long wheelbase (relatively speaking) and a very relaxed steering angle (33 degrees on the 98+ Kats), so it tends to dampen oscillations by itself when they are induced.

Lots of the sport-replica bikes (GSXR/R6/R1/etc) with their hyper-nimble steering are far more prone to this behavior, and thus a steering damper is a common accessory or may even be built-in by the factory (a steering damper puts a device to add resistance to rotational motion at the triple trees, helping clamp down on headshake).

One of the biggest problems with head-shake (the symptom that leads to accidents called tank-slappers) is that human muscles normally can't fire fast enough in response to the inputs to oppose them because of the signal time back and forth between the brain, so muscle input by less-than-ideally skilled riders tends to aggrevate the head-shake rather than clamp down on it.

When I was teaching riding in Germany, we taught our students that in such circumstances to try to curve their hand into a loose circle around the bars and lock the arms in one position as best as viable, so the headshake would oscillate through the circle limited by their hands (rather than having them trying to actively fight it and make it worse). In most situations, accompanied by releasing the throttle and light rear-brake input, the oscillations will stabilize and then die down (unfortunately not always -- but in cases where it wouldn't, the only things that would have helped at all in terms of driver input is praying or getting the front wheel to loft up so it's not in contact with the ground at all [and hope that when it comes back down the symptoms don't repeat]).

Cheers,
=-= The CyberPoet

[bobs]

Aren't bikes more prone to tankslappers if the CG is too far aft - e.g. with a passenger or luggage?

[Black_peter]

One of the biggest problems with head-shake (the symptom that leads to accidents called tank-slappers) is that human muscles normally can't fire fast enough in response to the inputs to oppose them because of the signal time back and forth between the brain, so muscle input by less-than-ideally skilled riders tends to aggrevate the head-shake rather than clamp down on it.

I think I did just that..
Once I relaxed my arms so did the bike..
(My butt required several days to relax however)

[The CyberPoet]

Aren't bikes more prone to tankslappers if the CG is too far aft - e.g. with a passenger or luggage?

As far as I can figure, only in the sense that it may make the load weight on the front wheel lighter (either because of weight shift rearwards or because of changes in how the traction is applied on-throttle), thus less down-force to act as a dampening influence at the tire/road grip interface.

Cheers,
=-= The CyberPoet

[jgalar]

If you have a tank slapper and live to tell about it you will never want to repeat the event. A tank slapper is when head shake gets so severe that the bars violently and very rapidly oscillate from stop to stop.

All front tires will wander or oscillate from center, but the effect is dampened by tire and steering head bearing friction as well as rider input. Loose wheel bearing or swingarm bearings will also increase headshake, also tire condition and balance.

Recently while riding my 2001 Katana I was coming to a stop and took my hands off the bars and leaned back to stretch. When the bike slowed to 45mph the bike went into a headshake. As soon as I grabbed the bars the headshake stopped. Being not so young, but still dumb (I'm 50) I decided to see how far the headshake would go without rider input. I accelerated to above 45 and let go. At 45 the headshake returned and by the time it got down to 35mph it was shaking more violently than my drawers can tolerate. Grabbing the bars and shifting the weight back onto the front tire stopped the headshake. Turning around and looking at the road where I had just traveled I noticed tire marks where the front wheel had been bouncing violently like this...
\
/
\
/

I have experimented with letting go at various speeds up to 70mph, but the 45mph point is where my headshake starts. I have noticed a little bar vibration at 45mph ever since I have owned the bike.

If you try you can induce a headshake on any bike and sometimes without trying. Headshake is caused by a change in the friction equation or a voodo curse upon you. If the friction is lessened, such as when your bike crests the top of a hill and the front wheel gets light, and the natural tire/wheel oscillations get in synch with the front end the bike will shake.

To stop a headshake you need to change the friction equation and/or remove the voodo curse. You may be able to accelerate if the shake isn't too bad. The best bet is to apply rear brake to increase the front tire friction.

Keeping your steering head bearings, wheel bearings, swingarm bearings etc in good shape is the best method for preventing voodo curses.

There is a reason why race bikes are required to have steering dampeners!

[skasner]

jgalar... sounds like your front tire is deformed/cupped or something. i had a similar problem with my kat and when i replaced the tires it went away completely.

[jgalar]

Nah, everything is fine. It is just the bike wasn't designed to be ridden without your hands on the bars and your weight shifted all the way to the back tire No shimmies or shakes when I'm in a normal riding position. Was just trying to illustrate what a headshake/tank slapper is. I now know not to lean back and take a smoke break when doing 45mph.

[The CyberPoet]

jgalar... sounds like your front tire is deformed/cupped or something. i had a similar problem with my kat and when i replaced the tires it went away completely.

I'm inclined to agree... I've owned a couple Kats, and the only times that I got bad headshake at 45 was a result of worn-to-the-point-of-defective tires. Changing tire brand/type made a world of difference as well.

Cheers,
=-= The CyberPoet

[skasner]

Nah, everything is fine. It is just the bike wasn't designed to be ridden without your hands on the bars and your weight shifted all the way to the back tire No shimmies or shakes when I'm in a normal riding position. Was just trying to illustrate what a headshake/tank slapper is. I now know not to lean back and take a smoke break when doing 45mph.

I can ride solo w/ no-hands at 45mph+ on my 99Kat sitting on the passenger seat or standing on the passenger pegs with no hint of headshake.

Yes... I did it during my lunch break.

Yes... I know it isn't the most intelligent thing to do.