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Discussion Starter #1 (Edited)
My buddy went down yesterday. Number one lane of a busy Los Angeles freeway. He's fine (mostly), bike is totaled. Says the handle bars started "tank slapping" (that's when they start gyrating side to side, and "slap" the side of a MC fuel tank uncontrollably. Usually starts by hitting something with the front tire.)

He said he just tried to hang on, but got thrown off the bike. This was my advice to him and my other riding buddies...

"The dreaded tank slap is a hard one to recover from. I used to ride off-road bicycles. Riding downhill they would go very fast and the handlebars would do the same type of affect. If you suddenly grab them tightly and "just try to hang on", the side to side energy being expended would surely "buck" you off (I suspect that's what happened to you). I found holding the grips very loosely, like hands in a four inch claw, and letting them bounce around inside, gently guiding the handle bars left or right, was the only way to remain in some sort of control.

To stop, I would slowly apply brakes, still letting the handlebars slap a bit, and as the bike slowed and the side to side energy decreased, I could tighten my grip and come to a somewhat controlled stop.

A couple years back, I hit a pothole so deep and hard, the rear end of the 400 came up. The bars started to tank slap, bad. So I loosened my grip, let them slap around a bit, applied brakes slowly and then tightened my grip slowly, easing it back into control... Disaster averted. The whole point is not to fight the bike or the bars, its a bucking bronco at that point. As counter intuitive as it may feel to do, you must let go a bit and slowly regain control. Speech over. But I wanted everyone to read that for their own edifice."

I'd be interested to hear what other experienced riders think of this advice and or proffer some other wisdom. I don't profess to "know it all". So if this helps someone in the same situation, great! If there is some other learned advice on how to "thwart the slap", we'd all love to have another tool in our riding toolbox.
 

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What bike was he riding, a Burgman?
 

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Unless you can ride it out, or throttle out to carry the front end, you're done.
I do agree, the death grip probably isn't the best route to go, but not a human being on earth is going to let go of their grips when they start to violently shake!
 

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Discussion Starter #4

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Discussion Starter #5
Unless you can ride it out, or throttle out to carry the front end, you're done.
I do agree, the death grip probably isn't the best route to go, but not a human being on earth is going to let go of their grips when they start to violently shake!
I did. Well not let go completely. It's just a situation that requires finesse, not brute strength. The bike is much stronger than you at the point where it is slapping. Bearing down with all your might will only buck you off in the direction the bars happen to be when you death grip. I found if you let it do its thing and slowly bleed off the gyrating forces, you can stay up right. Just don't panic. Have this maneuver in your riding skills toolbox, and try to finesse it out. IMHO.
 

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Discussion Starter #6
I should clarify something a bit. I think there are levels of this phenomena. If your handlebars are honestly and truly tank slapping, all the way from one side to the other, you are completely out control and there is probably little you can do to save it.

However, I've experienced smaller versions of this where its starts out with only an inch or two of wobble. This is when the maneuver I proposed works best. If left unchecked, the wobble will get worse and turn into full blown tank slapping within a few seconds.

With My experience hitting the pot hole, it started as fairly large wobble and within 2 seconds there was probably four inches of travel side to side in the gyrations, had I done nothing, it would have been full blown TS.

I truly hope this help someone some day.
 

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In all my years of riding I have never experienced a tank slapper so not sure how I would react if one occurred. Closest I have come is to have the head shake a couple of times. On those occasions I have just basically ignored it and didn't fight it. It corrected it's self in short order.
 

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I've had it several times on high speed motocross tracks, and I'd rather go down a mine shaft then a tank slapper! Frightening. Like stated, way more force then you can possibly fight. I cought it once when my hands "blew off" the bars I somehow ended up with. The clutch lever in my hand and saved it, again, I think I'd rather of gone down, less poop.....
 

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Braking will usually make it worse - more weight transfer the front will increase the severity of tank slapper. Also, trying to hang on tighter will transfer the energy of the bars into the rest of the motorcycle chassis through your body. The best solution is that when you feel a tank slapper starting, get on the gas and move your body backwards on the bike. You need to get the weight off the front tire to stop of the slapper. Unfortunately, if your bike goes into a slapper because you've hit something, it's really hard to save. Generally speaking, you'll be off the bike before you can do anything to fix the situation.

A tank slapper occurs when the front tire stars skidding from side to side in harmonic frequency with the front suspension. So you get a skid/bounce, skid/bounce, back and forth. If you look at the road after a tank slapper, you'll see a bunch of little half-moon skid marks alternating left and right down the road.

Get the weight off the front of the bike; either by getting on the gas or by getting away from the front of the bike.
 

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I think we need to come up with a new name for this condition for our tankless bikes. :p
 

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Hammer aren't knee knockers what they used to call the longer shorts that came down to your knees? And yes I'd agree that "Knee Knocker" would fit that condition for our scooters.
 

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The shorts sound familiar. I didn't use 'em model28a. "Knee Knocker" may be useful on two counts as it may describe the physical action of the bike and rider, and the mental state of the rider. I do believe that knee knocking comes just before p**p. lol
 

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I had it happen to me recently on the highway doing 70mph and it is a scary situation for sure. (Posted here:: http://burgmanusa.com/forums/12-general-discussion/90802-tuck-roll-swan-dive.html)
Riding it out is your best option if you can. On a conventional bike the foot brake (rear brake) is you best friend in that situation but on a scooter rolling off the throttle and let the engine braking help is the way to go. If you tense up and try to over power it handler bars you will go down. It is hard to relax in a crisis but it will give you the best chance to ride out of it.
 

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Discussion Starter #15

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I think the tiny front wheel of the Vespa contributes to the problem. It happened to my friend many years ago right after I painted the bike for him. He hit a small pothole and couldn't correct. Mark
 

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In all my years of riding I have never experienced a tank slapper so not sure how I would react if one occurred. Closest I have come is to have the head shake a couple of times. On those occasions I have just basically ignored it and didn't fight it. It corrected it's self in short order.
Back years ago when I was on a B400...there was talk that with some of them, they'd go into death wobble up in the high 70s speeds.

It's basically an harmonic issue...a wheel out of balance, perhaps inherently, with a chassis that's given to resonating a certain way at certain speeds when strummed with engine vibration. A pothole can launch it, but unless there's something wrong, either with chassis design or with a wheel or tire...it won't happen.

I felt it start once on my 400, at about 80 mph (the banzai run that later I found burned out bearings in the variator) I backed off; there wasn't much more speed in there anyway, it came right down and the shake went away.

Never had it on the 650. Never had it on the BMWs I've owned, or the Silver Wing (motorcycle, not scooter; early 1980s). But then, mostly I've had smaller machines, not sport racers.
 

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Had a minor TS on my 05 Concours, because I lowered the front end about 1 inch. Which stood the forks a little more vertical. Was going about 40. Yes I put it back to stock height as soon as I was home again! Not a good feeling.
Later, after I dropped the same bike (slow speed high-side from a slide) I put Progressive springs on it, but what really helped was the Fork Brace ($80), you would have thunk the forks were made of spaghetti before that. Rock-solid.

Which we can't add to Burgie, with its stub-forks. But I have never had a panic situation with Burgie.
Keep the tires inflated, check steering stem for looseness, check all fasteners and you should be fine.
 

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Which we can't add to Burgie, with its stub-forks.
You must have a 400, there would be no problem putting a fork brace on a 650 as it has a regular double clamp front fork like most motorcycles.
 

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I think the tiny front wheel of the Vespa contributes to the problem. It happened to my friend many years ago right after I painted the bike for him. He hit a small pothole and couldn't correct. Mark
IMHO that style of scooter has no business on the freeway at freeway speeds . Just because a scooter can go those speeds doesn't mean you should .

TheReaper!
 
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