Tank Slapper?

[California]

Any one here ever experience a tank slapper?

What causes the phenomenon known as a tank slapper? I mean, what's the physics and engineering behind a "tank slapper"?

All my life, I've heard people talk about it, I've read articles where it's blamed for accidents, injuries, and all kinds of ecological, global warming, icecap melting type things, but until recently, I'd never experienced, nor seen it happen

3 times, on three different days, on three different rides, in relatively hard, longish type corners, and with a certain amount of warning, I've experience this on the Tenere, and I'm at a loss to know what would cause it, and what the hell is going on that those kind of forces exerting themselves on the front end. The only thing that has stopped it is bringing the bike back to an upright position and dragging the speed back to a virtual stop. The part I really don't understand, all three times, I've continued on with my ride, and done craploads of corners at the same or higher speeds and duration, and not another slapper was given that day?

Anybody, somebody?

Explain "tank slapper" to me and tell me what to do?

 

[tomatocity]

Before making any adjustments... air your tires up to 38F 42R. See if there is a difference. I say this because I recently changed tires and was experiencing the same tank slapper issue. Aired the tires and tank slapper was gone and along with much better handling.

 

[avc8130]

I highly doubt you were experiencing a "tank slapper". The Tenere geometry makes a tank slapper VERY unlikely.

Generally the solution to a tank slapper is to stay on the gas and try to keep the rear sliding until it gets back inline with the front.

Your post is very confusing. You ask what a tank slapper is and how to prevent it, but then you state you have experienced them...3 times! What is REALLY going on?

ac

 

[tc9988]

I highly doubt you were experiencing a "tank slapper". The Tenere geometry makes a tank slapper VERY unlikely.

Generally the solution to a tank slapper is to stay on the gas and try to keep the rear sliding until it gets back inline with the front.

Your post is very confusing. You ask what a tank slapper is and how to prevent it, but then you state you have experienced them...3 times! What is REALLY going on?

ac

really

 

[tomatocity]

Not true ac. I have created (not trying to) the loose feel of a tank slapper while chasing suspension settings. Ride down the freeway and shake the handlebars and the Tenere would be looooose. Finally got the suspension close to good and changed tires. Was riding the river road and it did not feel good so I shook the handlebars and sure enough it was loose again. For other reasons I increased the tire pressures that night. Rode the same roads the next day and the induced shakes were gone, surprising. I never felt the Tenere go into a tank slapper on its own and you are right the Tenere is very stable but it can be induced with improper suspension and tire pressure settings.

 

[GrahamD]

The term tank slapper used to used for when the bars whacked the tank, it was that bad.

Now people use it to prove how baddass they are at recovering or an excuse for coming off after freaking out after a wobble.

These are major wobbles and some possible "slappers" but if your tank is not touched it's technically not a slapper. Doesn't really matter it's a shitty feeling either way.

Best Moto Wobbles, Tank Slapper Moments (saves and crashes)

This is a wobble or oscillation.
Oscillation

 

[snakebitten]

With the Tenere's geometry, you got something pretty wrong if the bike experiences a classic tankslapper. It's just not a nervous setup.

 

[California]

A clarification,,,

I know what a tank slapper is.......

I was wondering what the physics and engineering are associated with it.


I'm having a hard time getting my head around the fact that an otherwise stable piece of machinery can suddenly start oscilating so badly that it takes all the strength I have in my arms to control it and that nothing I do caused the back and forth oscillation of the handlebars to cease until the bike was back down to perhaps 10mph. Are the front forks twisting while this is happening? Is there enough force to cause damage to anything? Can a bad tire do this? I am quite sure that if I didn't "clamp down, and try to \\straight arm the handlebars, that it would literally oscillate through the entire range of motion allowed by the triple tree stops and I would quite literally end up either thrown off the bike or would end up going down in a rather extreme fashion.

The first time it happened, maybe three weeks ago, I had been messing with the tire pressure, and had lowered it to about 34. I presumed that to be the cause and reinflated it to 38.

The second time it happened, last weekend on my way to meet up with a group for a 200 mile ride, I thought, maybe it was becasue the tire was cold, perhaps there was a flatspotfrom being parked for a week, and then for the rest of the ride, a relatively spirited ride,

The third time was this morning. 55 minutes into the ride, in a sweeping right hander at about 60mph, there was a slight warning wobble, and then BANG, full back an forth, tank slapper. If there hadn't been a drive way on the outside of the turn for me to ride straight off as I slowe down, I would have surely ended up in the ditch.

I want to know what causes these kinds of things, and has anyone ever experience it on a Tenere. What should I look for to make sure it doesn't happen again?

 

[California]

The video has exactly what I'm talking about. That is exactly what it does, and you can see how hard it is to get it back under control. p.s. GrahamD...The fact that parts don't actually contact the tank is a ridiculous reason to not call it is what it is. The reason parts aren't contacting the tank is that they are properly installed and adjusted so that under no circumstance could they contact the tank.

As a bit more info, in case you didn't know, this is the Tenere that used to belong to Japaco, and nothing has been altered, or changed since I got it from him, except that I've put almost 3,000 more mile on it.

 

[snakebitten]

Wow. Not good. But I will say this........

I have been on this board for more than 2 years. I have read every single post for those 2 years. (yea. I'm sick)

You are the only person to have raised this subject on the Tenere. I assure you, it is not common on this bike. You have something that needs to be addressed.

Good luck. Be careful.

 

[MojoToot]

some bikes are prone to this problem...a steering damper can help.

but this problem is usually related to the front end becoming light & something sets off a force which the rider trys to compensate (overcompensates) & it continues in an (often) escalating fashion.

Here you are having this problem in a turn. This is NOT typical of a tank slapper.

I am wondering about bags/topcase & weight ditribution?

Where you using brakes or trail braking in these turns?

Were you accelerating or decelerating?

Give us ALL the details you can remember.

 

[cosmic]

Tank slap or just a slap it can happen, i'am sure of it, but then you will most probably be f.cked. At least with this kind of monster. I live in a very,very slippery city. Most of the downtown roads are so polished, that you can drift around with the 300cc scooter. I have been sliding around for the last 20 years, and i enjoy it, but just sometimes i get carried away, and find my self with both legs in the air, avoiding high side only on pure luck. Not always though.

Now, i cannot see the clips above, but i guess their feet are up in the air, if the slap is worth anything.




©

 

[avc8130]

Not true ac. I have created (not trying to) the loose feel of a tank slapper while chasing suspension settings. Ride down the freeway and shake the handlebars and the Tenere would be looooose. Finally got the suspension close to good and changed tires. Was riding the river road and it did not feel good so I shook the handlebars and sure enough it was loose again. For other reasons I increased the tire pressures that night. Rode the same roads the next day and the induced shakes were gone, surprising. I never felt the Tenere go into a tank slapper on its own and you are right the Tenere is very stable but it can be induced with improper suspension and tire pressure settings.

"Loose" is most certainly NOT a tank slapper. A tank slapper is a wobble that AMPLIFIES rather than damps out. I have been ALL OVER with my Tenere suspension setup and I NEVER been able to create a wobble that amplified itself. I currently run my rear sag less than "normal", have my triples dropped 10mm AND run a bit more sag up front. This SHOULD make the bike about as twitchy as possible. It is STILL ridiculously stable. The Tenere geometry is so lax from the factory. This bike has TONS of trail...probably why it works so well "off road".

Shaking the handlebars and feeling "loose" is relatively normal.

https://www.youtube.com/watch?v=SkDPMLxAZP0

ac

 

[snakebitten]

Japako's bike was meticulously setup and cared for. I have confidence that it was sound.

But he did rig it as a pack mule. Big Micatechs, and the full pillion conversion for additional top load.
In other words, it would let you pile on big time.

But even so, I have ran the Tenere at full allowable gross weight. (450lbs) And although the rear oem shock struggled with it, the handling was still safe.

I ride everyday. For more than 40 years. I've only had 3 tankslappers in all that time. 3 in a row on the Tenere is just bizarre.

I'd set all suspension setting to factory. Then work from there.

I don't believe the front tire pressure of 34lbs caused it. The bike isn't that temperamental.

 

[avc8130]

A clarification,,,

I know what a tank slapper is.......

I was wondering what the physics and engineering are associated with it.


I'm having a hard time getting my head around the fact that an otherwise stable piece of machinery can suddenly start oscilating so badly that it takes all the strength I have in my arms to control it and that nothing I do caused the back and forth oscillation of the handlebars to cease until the bike was back down to perhaps 10mph. Are the front forks twisting while this is happening? Is there enough force to cause damage to anything? Can a bad tire do this? I am quite sure that if I didn't "clamp down, and try to \\straight arm the handlebars, that it would literally oscillate through the entire range of motion allowed by the triple tree stops and I would quite literally end up either thrown off the bike or would end up going down in a rather extreme fashion.

The first time it happened, maybe three weeks ago, I had been messing with the tire pressure, and had lowered it to about 34. I presumed that to be the cause and reinflated it to 38.

The second time it happened, last weekend on my way to meet up with a group for a 200 mile ride, I thought, maybe it was becasue the tire was cold, perhaps there was a flatspotfrom being parked for a week, and then for the rest of the ride, a relatively spirited ride,

The third time was this morning. 55 minutes into the ride, in a sweeping right hander at about 60mph, there was a slight warning wobble, and then BANG, full back an forth, tank slapper. If there hadn't been a drive way on the outside of the turn for me to ride straight off as I slowe down, I would have surely ended up in the ditch.

I want to know what causes these kinds of things, and has anyone ever experience it on a Tenere. What should I look for to make sure it doesn't happen again?

You don't happen to be running a Continental Trail Attack front tire...do you?

I experienced EXACTLY what you are describing on Swampy's Tenere when we were down in NC last year. It turns out that tire just did NOT work on the Tenere. Revzilla sent a replacement to Wheelers and they covered the change. The 2nd tire did the EXACT same thing. The bike would start to wobble and it took all the effort to hang on. It didn't amplify up, but it was certainly unsettling.

ac

 

[GrahamD]

The video has exactly what I'm talking about. That is exactly what it does, and you can see how hard it is to get it back under control. p.s. GrahamD...The fact that parts don't actually contact the tank is a ridiculous reason to not call it is what it is.

8) Now settle down.. ;D

It maybe should be called a Stop slapper or high amplitude oscillation. If it doesn't slap the tank it isn't a tank slapper is it, but it might still be a poo producer.

Anyway what ever. I have seen slight wobbles called tank slappers and very quick wobbles called tank slappers, you know the ones when the front wheel is off centre when it comes down and it has a big "decreasing amplitude shake" as it settles down.

So now we all know what you are talking about, which is all I wanted to get to.

So scalloped tread is one. loose bearings, loose clamps. overweight on the rear. flat tire (especially on blocky thin walled tires), just plain funny tires that don't work with the bike or a combination of all the above. ???

The tenere has relatively stiff suspension, IE laterally, slow steering geometry, and a pretty chunky stiff frame, normally set up it's lucky to turn a corner

OK it's not that bad it's just slower and more stable than most bikes are set up. Can't add much more to look for that I can think of right now.

There is a extremely small possibility that there may be a Frame problem. Not the first thing I would be looking for though.

 

[Combo]

If it ever happens on any bike, what seems to work the best to get out of it is to real quick: push forward on the bars, squeeze your leggs together and roll on the gas all at about the same time you are filling your shorts. Letting off of the gas is bad when it starts to happen. I know turning on the gas is not what you want to do at the time but that is what will save you.
I used to ride Z1's

If you are at WFO when it happens the only Maneuver left is to see if you can reach around your lips to your ass. ???

 

[zamfield]

Sounds like its probably your luggage, not the bike its self.
If you are running the top case along with side cases you are definitely making the front lighter so having less contact with the road surface.
You'll notice most of the tank slappers happen when they're coming down from a wheelie or accelerating out of corners where theres less weight on that front wheel.

It could also be riding style, or a combination of both.
Try sitting forward on the seat.
I see many riders sitting way to far back and with a loaded bike can cause it to lift up in rough terrain or hard acceleration over bumps etc.

 

[cosmic]

Sounds like its probably your luggage, not the bike its self.
If you are running the top case along with side cases you are definitely making the front lighter so having less contact with the road surface.
You'll notice most of the tank slappers happen when they're coming down from a wheelie or accelerating out of corners where theres less weight on that front wheel.

It could also be riding style, or a combination of both.
Try sitting forward on the seat.
I see many riders sitting way to far back and with a loaded bike can cause it to lift up in rough terrain or hard acceleration over bumps etc.

Just now, after reading Zamfield's post, i realized that i confused shimmy with something completely different.
Well, then i have to be honest, in 20tkm it never happend to me.


©

 

[California]

While the bike does have big luggage, it's never happened when there was anything in the luggage, nor if my wife was on board. In fact we did 1200 miles one weekend in the hill country, all on pavement, without even the slightest wobble.

No, they are not Conti Trail Attacks, They are Battle Wings.

Jim did lower the bike, is there any chance that a change in geometry made this possible? the front is down by sliding the tubes up about 1/2 inch and changing the links in the rear to lower it 3/4 inch.

I think the part of this that confounds me the most, is that it can happen, and then not happen again for hundreds of miles, hundred of turns. One would think that if there were a problem that could manifest itself so dramatically, that it would do it regularly, or the rider would be able to reproduce it at will. If it does it in corner x, sweeping right, at 45 mph, why cant I get it to do it there again? I know it may sound idiotic, but I've tried. Really? Who would want to risk possibly crashing, on purpose? I've been back to the same turn and ridden through at the same speed and, nothing?