Tank slapper

[oldbike54]

 Charlie B is on to it here . What most describe as a weave is due to chassis and swingarm flex inducing a slight back and forth movement . A true tank slapper is caused by front tire deflection . The giant gyro up front is trying to self correct , in the process it over centers several times , finally coming back to center , hopefully 

 Dusty

[mgfan]

Had one on a naked 82 goldwing, going slightly uphill on a left hand sweeper. Just coasting off throttle going about 65. Started the violent head shake and I won't say I knew what I was doing but stomped on the rear brake and recouvered. It only ever did it on the 1 particular freeway exit and never did it again. 

[lucian]

Never had it happen yet that I can remember but I am wondering if it has to do with flex in the chassis allowing the front to adopt a different line than the back. The front would then  try and correct, but at speed would become a series of over shot corrections. The similar analogy would be while ice skating with both blades in line . I can remember while learning this as a youngster if the front blade got even slightly misaligned a horrendous wobble could result.  I am not certain that a steering damper would even help in this situation as once out of line,  the front will violently try and correct. Depending on speed the pulses back in forth would change in wave length but I would think it would be uncontrollable and would only end when re alignment is achieved or bike and rider are on the ground. I have always thought that the most important safety feature on a m.c. is chassis rigidity.

[guzzisteve]

I was tuning a customers 85 LM doing the wide open circuit when it hit 125 it started a shake, when it hit the stops the second time is when I tried the brakes.  Accelerating wasn't working, letting off the gas loaded the front and it got worse.
I didn't really want to trash a new bike. First LM to have Koni  shocks. They were so fast compared to a LM3.

[arveno]

when :May 26 th 2013 , around 4 pm

bike : 1980 moto guzzi sp 1000 le mans clone

location : crappy  NY highway .

I had a tank splapping at 90 mph..... i am glad i am here to tell the story...( and glad the cars behind me had good brakes )

Right after i put a set of new fac dumpers i took off to try the bike.... the front end felt good but way too stiff .
I ran over some crappy/uneven asfalt , front end started slapping ....went down on my left side , hit the ground with the helmet 3 times ( thank you Aray ) and left shoulder.... i turned on my back while sliding on the ground ( thank god i had a back pack with a pair of brand new sneakers inside  ) .....
I never wear boots /gloves and leather jacket but that day they saved my fingers /feet and left arm .

[jbell]

Not a tank slapper, but a high speed wobble on an Eldorado.  Wrong front tire.

[lucky phil]

https://www.youtube.com/watch?v=LW0UAgzntao

this would be better if he fell on his ass.


#93

There wasn't one single tank slapper in that whole video.
Ciao

[Moz]

I always understood the long legged tontis were less inclined to tank slap - even though they came with steering dampers?  so a shorter chassis and steep rake more likely..

[ohiorider]

If any of you who have experienced a handlebar wobble think that is a tank slapper ..... well, sorry to tell you, a tank slapper is just that ..... the bars bang harshly against the steering stops, and the bike is totally uncontrollable.  And believe me, you don't have enough arm strength to hold the bars steady.  It is a mechanical animal totally out of control  ....  the laws of physics have taken over!

2x for me.  First was nearly 50 years ago, on my BSA Spitfire Scrambler.  Second time, and a huge surprise, on my BMW R100GS, and not at more than 30mph. 

An amazing thing ....!

Bob

[DARKHORSE]

Mine happened on a 96 gsxr 750. Crested the top of a hill and had five cars  in front of me. The lead car decided to make a left turn but stopped in the turn causing everybody to brake hard. My slapper started immediately and started to shake violently. No room to do anything with the throttle so i let off the front brake and started alternating back and front brake, got me out of the slapper. Talk about butt pucker! Why did it happen? My take on it is a lot of stored energy while braking and a short wheelbase. Stay loose my friends, I think that was the only thing that saved the day.

[lucky phil]

If any of you who have experienced a handlebar wobbler think that is a tank slapper ..... well, sorry to tell you, a tank slapper is just that ..... the bars bang harshly against the steering stops, and the bike is totally uncontrollable.  And believe me, you don't have enough arm strength to hold the bars steady.  It is a mechanical animal totally out of control  ....  the laws of physics have taken over!

2x for me.  First was nearly 50 years ago, on my BSA Spitfire Scrambler.  Second time, and a huge surprise, on my BMW R100GS, and not at more than 30mph. 

An amazing thing ....!

Bob

You are correct Bob. With a full blown tank slapper you are a passenger, hang on and pray as the steering goes stop to stop.
A weave which can lead to a tank slapper is something you can ride out of if you know how, generally by getting hard on the gas.
I experienced a slapper coming onto the straight at Phillip Island on my GSXR1000 about 3 years ago. Hard on the gas onto the straight and pick the front wheel up an inch or so as usual but this time it came down slightly crossed up. Forget about any ability to apply technique,way too violent for that. On about the 3rd hit of the steering stops it straightened up but I was just hanging on for dear life thinking I'm going to be off this thing in a straight line in front of the pits, how bad will that look.
Then I got to turn 1 without any front brakes due to brake pad knock off due to the violence of the slapper. Fortunately i was half prepared for that and some furious pumping of the lever got them back.
Next visit to the track I had replaced the std damper with an Ohlins unit adjusted so tight I couldnt ride it around the pits,ha.
Got over it though after a couple of sessions.
Ciao   

[leroysch]

I have never owned a bike that did it, but I have ridden a few.

One in particular was a Suzuki 500 twin, the 2 stroke. Taking hands off the bars caused a massive wobble. Oddly my brother's 500 didn't do this.

Interesting. My experience too. Suzuki Titan 500 2 stroke street bike, crossing over some railroad tracks at a sedate speed. Went from lock-to-lock, all I could do was let it run its course. Made a big impression on me, since I owned that bike back in the mid-70's and STILL remember it.

[Sasquatch Jim]

 In 66 I was northbound on a two lane in Illinois.  Coming towards me at about 70 or more was a BMW with earles forks.
 I saw him wobble then go into a full house tank slapper then down on his left side just before he slid past me.  With my wife on the pillion, I still was able to get slowed and U turn in time to se his bike slide to a stop.  He was lying unconcious
 in the middle of his lane and the bike was three telephone poles further and on the shoulder.  Leaving my wife with him I raced to a farm house and called police.  After the ambulance took him away, the leo and myself examined the bike.
 I pointed out the steering damper, a hydraulic shock absorber type, had snapped off from one of its mountings.  I would bet that it snapped under strain and that allowed the tank slapper.  It was the most violent tank slapper I can remember seeing.

[cruzziguzzi]

I'm with DRLAPO - worst and really only full on "tank slapper" for me was on my Hodaka; either my Super Rat or Wombat, I don't quite recall which... Both? In any case, it wasn't a Combat Wombat. I figure my mere Wombat was the conscientious objector of the line.

Anyhow - I do recall the incident in that I was blasting along the railroad tracks outside of Anoka, Minnesota. Being completely beyond rational or analytical thought as it was the first time I was able to get it into top gear, I was little more than a pubescent meteor temporarily skimming the earth unwittingly waiting for inertia to tire with me and let gravity have its way.

My first sign that something might be amiss was the front getting a bit upset and by some cinders. Knowing little of the dynamics of what was going on - which is to say I had the vaguest notion as to why a motorcycle didn't' topple over - I paid no attention to how little contact the front tire really had with terra-oucha.

Of course, in 100-mile-an-hour-with-yer-hair-on-fire fashion, I had too much weight over the rear in my best "Then Came Bronson" riding style.

The cinders set the front a-twitter and the rest was me just waiting to see how it all played out.

I had a healthy though still insufficient respect for the tracks there in general and the cinders and ties in particular as we'd clashed in the past while snowmobiling along them. Great vast amounts of winter snow and ice might go a long way with adrenaline in temporarily muting the pain but I was still very conscious of the memory when I became an engaged bystander on my Hodaka.

I had maybe, what 3/4 - 1 1/2 seconds of alarm at the bars developing a mind of their own and then it was lock to lock, no half measures, hell in a hand basket horror as it shook holy hell outa me till my arms were thrown well off the bars.

By then I'd also been bitch slapped by all three of Sir Isaac's laws resulting in lost footing and repeated nard abuse.

Oddly, as is often the case in general and (not going unnoticed by me all these years) me in particular, nature took pity on a fool. In removing me from any significant input while having blessed me with an outstanding sense of balance, the world came back a-right as the bike slowed and I stayed on the chrome side.

Slow, stop, commence to shake and then I went back to see what I had hit - being completely ignorant of the concept of a "tank slapper" I assumed I'd been undone by some hobo-thrown trash. Walking along the cinders, one thought kept coming back to re-ignite the shivers and that was that I wouldn't be going home with bedding material in my skin without the benefit of early onset frostbite to see me through the trip as it had in winter.

Initially I had trouble reading the tracks but eventually I light upon some standard if light and dusty tracks. When I turn to follow them to the bike they all but disappear as anything approximating a motorcycle track and become this weird display of wildly though geometrically placed scuffs of impossible width in their presentation. The notion that the Hodaka was moving that insanely beneath me only made my tensions worse.

As I walked you could see just where it ceased to grow worse and immediately began to stabilize - this is probably where the cosmos jerked the last of my input from the scenario.

Man, but I'll tell ya, I sat for quite some time on the banking before starting that thing up again and then I never used up even third gear on the way back to the shop.

Since that swirling vortex of doom ride - I've figured everything else to be excessive weave.

And these include ill advised mods on top of poor maintenance of Kawasaki triples; 500 & 750 and failure to properly reassemble the front end of my '82 Katana including not replacing the factory front fork brace and then "test riding" it on suspect tires. Yup, that was a test alright!

Anyhow - Tank slappers? Yup and no thanks!


Todd.

[swordds]

An old but informative British study on wheel wobble.  I am surprised that how to handle this is not taught in basic training. I have had it happen only on bicycles and leaning down and forward has stopped the problem.

http://www.youtube.com/watch?v=z3OQTU-kE2s&sns=em. 

[LowRyter]

very good video.  I remember that some of those 70s bikes were a handful. 

Funny, they didn't run a Guzzi in their film.

[Dilliw]

My 1983 Suzuki GS750e (16" front) had a very predictable high speed wobble (those Brits in the video call it weave) north of a hundred mph.  Once you knew it was there it was no problem; you just needed to add more right hand.  If you stayed at the speed too long it would start getting interesting.

[pressureangle]

I've probably suffered more tankslappers on more different motorcycles than anyone else here. I hope so, anyway...

The two most common, as well as least known, causes are;
1. Loose steering head bearings.
2. Rider pulling backwards on handlebars instead of pushing.

#2 is by far the more common, and the worst; because this is usually caused by high speed and the rider in the wind.
If you get a scary weave at speed, lean forward and put weight on both bars. You'll find it goes away.

#1 is a death warrant if you find it the hard way, as I did twice on a racing H-D sportster. Setting bearing preload isn't hard, it's just tedious. But it's critical.

A few bikes seem to have a natural problem here; H-D FLT fixed-fairing dressers, which is usually fixed by keeping the air in the forks up to spec; and any Kawasaki 2-stroke triple. I was thrown from my '75 500 twice with no warning and collarboned myself once.

[motogman]

I was looking at a Suzuki 750 water buffalo as my potential next ride many years ago and took it for a test ride.  At about 70 mph the front end went into wild gyrations and scared the crap out out of me.  I slowed down and got it under control.  I rode slowly back to the owners home said - no thanks.

[malik]

A "violent weave" following a rear tyre blow-out at 100kph. With a truck behind, I chose to lay the bike over on the side of the road. New tyre and new tube 200km previously. I don't know if laying on the tankbag would have helped or not. Perhaps. "Forensic "analysis suggested a faulty weld of the valve stem to the extra thick tube. Lots of bent bits straightened, a bit of paint, ruined luggage replaced & another new tube, was back on the road in a couple of days, by which time the sore shoulder was fine. The armoured leather worked just peachy.

Mal

[Guido Valvole]

I've had two on the Monza. First passing a car at around 80 indicated (lol, 70 or so) with a strong crosswind. Front started to weave, building amplitude. I gently rolled off the throttle and pulled off the freeway at the first reasonable spot. Tire pressures were way too high. Plus crosswind, plus handlebar-mounted fairing that looks like it might have more lift than downforce.

Second time, also around 80 indicated, in deep nasty rain grooves with worn tires. Reasonable tread but cupping on the front and a bit squared off on the rear. That particular section of freeway is noticeably nasty even in a car.

Never a problem on the Le Mans with the 16" front wheel. Never a problem on the V50, so possibly the Monza fairing is suspect in some conditions. V50 has a Givi screen and 7" replacement headlight, so there's a bit of Lotus 25/33 venturi effect and possibly downforce at work.

Rain grooves are another problem…
cr

[ohiorider]

You are correct Bob. With a full blown tank slapper you are a passenger, hang on and pray as the steering goes stop to stop.
A weave which can lead to a tank slapper is something you can ride out of if you know how, generally by getting hard on the gas.
I experienced a slapper coming onto the straight at Phillip Island on my GSXR1000 about 3 years ago. Hard on the gas onto the straight and pick the front wheel up an inch or so as usual but this time it came down slightly crossed up. Forget about any ability to apply technique,way too violent for that. On about the 3rd hit of the steering stops it straightened up but I was just hanging on for dear life thinking I'm going to be off this thing in a straight line in front of the pits, how bad will that look.
Then I got to turn 1 without any front brakes due to brake pad knock off due to the violence of the slapper. Fortunately i was half prepared for that and some furious pumping of the lever got them back.
Next visit to the track I had replaced the std damper with an Ohlins unit adjusted so tight I couldnt ride it around the pits,ha.
Got over it though after a couple of sessions.
Ciao   

I can hardly imagine at racing speed!  It was so unusual ..... my Beemer went into a tank slapper at no more than 30mph in a turn after both front and rear tires slipped to the outside of the turn in unexpected gravel.  Damned bike 'walked' across the center line toward an electrified barbed wire fence with the steering banging off the fork stops.  So lucky that (a) no one was coming the other way, and (b) that the tank slapper quit on its own before I experienced the feeling of riding thru an electrified barbed wire fence! 

I could not believe the violence of the tank slapper at only 30 mph or so.

Bob

[Muzz]

Borrowed my bro's '53 AJS 500 to go sit an exam when I was still at school. The bike was well and truly "pre loved". Straightened up from going around a tightish corner at about 25mph when all hell broke loose. Handlebars whacking from side to side finishing with me being thrown up and off. As I lay there bleeding on the road an older guy wandered up and asked if I was all right. Well, I wasn't but I said I was. He looked at me and said, "in all my life I have never seen a bike do that"

Funnily enough, a few months later a bus did not give way to him and Tee boned him so hard it drove the corner of the battery case a couple of inches in to his leg.

50 years on and he still has the bike waiting to be repaired. Says it is the next cab off the rank after the Vincent....and after the De Soto and...........

[RayB]

There's a lot of experience posted here. What do we conclude about causes, predictability of the hazard, and prevention?

[Nic in Western NYS]

Never had one.  There's some basic physics going on that I don't understand but it seems like an unloaded front end from some cause is necessary for true TS.  I can't imagine a TS on the Sport 1100 remembering what riding it felt like - my weight was all over the front end considering that riding position.  It would seem like an upright riding position or a cruiser position is more likely to contribute than a sport position.  TS prevention might be a neat thing for some engineer working on traction control systems to take on.  Maybe a front tire sensor that indicates impending loss of traction - probably the whole event happens so fast that any warning would be too late though.

[giusto]

My conclusion on the tank slapper bit is that there are too many variables to boil this subject down to a few. Suspension, rider error, tires, road conditions, chassis design all enter into it. Our ignorance on the subject makes one re-think the risks we face riding motorcycles.

Yes well put....and add to this rider choices...I can't think of a good reason to take both hands off the bars...only bad results can happen.

[drw916]

1986  on a Honda CB1100F.   At about 85 I came around a corner and up ahead was a State Patrol with radar.  I hit the brakes hard and went into a full blown lock to lock tank slapper.  Have no idea what I did at that point.  I think I stayed on the brakes.  It ended up tossing me off the bike and earning me my first and only trip to the hospital due to a crash. 

Never did figure out what caused it, so I blamed it on the bike rather than me and moved on to a Kawasaki Ninja 750.