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Seen this on Sportsrider !

1. The “tankslapper” is a very frightening experience. Usually occuring when accelerating hard over bumpy pavement, a tankslapper ensues when the front tyre becomes airborne, then regains traction outside the rear tyre’s alignment. The resulting deflection bounces the tyre off to one side, followed by another bounce in the opposite direction as it contacts the pavement again. Unless the bike’s steering geometry is able to damp out the deflections quickly, the resulting oscillations from the front tyre as it bounces back and forth will swiftly gain in strength, causing the bars to swap from side to side with increasing ferocity. The oscillations can be violent enough to rip the bars out of your hands, and fling your feet off the pegs. You can guess what happens next.

2. The easy cure for this problem is a steering damper. Many sports bikes now come stock with one, as the radical steering geometry needed for quick handling can otherwise cause some instability in certain situations. While a steering damper is an easy fix, it shouldn’t be a cure-all; if you’re forced to adjust the steering damper’s stiffness (if available) until you can barely turn the bars in order to keep the bike’s handling stable, there is a problem somewhere in your chassis setup. A too-stiff steering damper can also cause handling problems by itself; if your steering damper is adjustable, and you find that your bike won’t hold a line (especially in slower corners), or gets into a small wobble or oscillation in high speed corners, try backing off the stiffness a little and see if it helps.

3. Not all sports bikes need a steering damper, however. Many have steering geometry setups that offer quick handling, while still providing the necessary stability to damp out any front-end oscillations. In most cases, one of the biggest contributors to a tankslapper is your body positioning and grip on the bars. Some people ride in a more upright position when carving corners, but when accelerating over bumpy pavement, that upright body position puts even more weight transfer to the rear, which causes the front end to get lighter. Also, the more upright torso means that your grip on the bars is tighter in order to stabilize your upper body. That firmer grip feeds more input into the front end, something it doesn’t need while it’s busy trying to damp out the inputs from the bouncing front tyre. It actually forms a vicious circle: you grip the bars tighter because they’re starting to flap back and forth, but that only feeds more input into the front end, compounding the problem further.

4. The easiest way to avoid tankslappers while accelerating over bumpy pavement is to—believe it or not—keep a relaxed grip on the bars. Relaxing your grip on the bars means you must lean forward in order to assist in keeping your torso stabilized. This helps put more weight on the front end, which keeps the front tyre on the pavement. Since you’re not using your arms to stabilize your upper body, get your weight onto the footpegs so that you can get your body as far forward as possible; this also allows you to grip the tank with your knees for more stability.

If you do get into a tankslapper, keep your weight forward and—as hard as this sounds—maintain a relaxed grip on the bars. Let the motorcycle’s chassis deal with damping out the oscillations. Don’t try to be a human steering damper; you’ll only make the problem worse. Tankslappers can definitely soil your undies; but if you’re able to deal with them correctly, you’ll usually ride through them before you know it.


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Ride on ! :)
 

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:goodpost: Thanks.
 

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Wooooof

I had one of these today. Was accelerating and changed lanes heading northbound on LaCienega in LA, had about 5-6 shakes. It actually never got to full-blown tank slapping, but it was pretty scary before it corrected itself.

I'm pretty sure I "tried" to correct it with my arms, which seemed to work this time I guess. I probably got lucky . . .
 

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There is some good explanation there, but I don't agree with anything written under point #4!.

You can't grip the bars tight when you're in a full-blown tankslapper! It's all a rider can do just to hold on to the grips. I don't see how you can even think of, yet alone pysically do, in terms of altering your weight position. I also don't think it would make any difference.

The only way to get out of a tankslapper is to change speed. And change speed as fast as possible.

The normal way is to keep the throttle open and accelerate hard. Once, however, there was a traffic queue in front of me when I hit a ridged piece of road where the road was being resurfaced. It sent me in to a violent lock to lock tankslapper. I had to brake very hard. The oscillations lessened & then stopped. It was a very hairy experience :(.

DaveB.
 

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In a tank slapper the bike is trying rid itself of a handling problem, the rider. The bike will right itself if you move your weight forward and have virtually no input in the bars, and a very light grip. A motorcycle is a large gyro, and will right itself.
 

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Tank Slapper : 1 Sims : 0

Heya, I saw the post about tank slappers above, it is true, the less you grip the bars the easier it is for the bike to sort itself out. I live by the rule of 'Relax, don't panic! and don't react!'

I've got myself into trouble a few times before but staying calm and relxed means I'm not upsetting the bike and making the situation worse.

The best example of this was last March I was on my way to work (Motorcycle Touring Company in New Zealand). I was on a straight road and slowed for a school bus that was picking up rural kiddies and taking them into town. I got past the bus and pinned it, changing through the gears quickly when all of a sudden I hit a rise in the road and some bumps. Normally not a problem, but as the bike started I grip the bars and tried to avoid a rock in the middle of my lane. Didn't work, the light front end, plus bumps, plus input from me and a tight grip on the bars resulted in the most horrific tank slapper I've ever known. The bike was out of control, ended up pushing me onto the grass verge (ahhh! Grass!) and spat me off.

Needless to say I was chewing cloth, which was getting stained at the same time and both the bike and I shot down the verge at 100+ kmh. The unfortunate thing was the bike dug into the dirt and went into self-destruct mode, I got up after my gracefull slide along the grass (ahhh! Grass!) and below is a link to what I was confroted with. Ooops!

Stay Calm, Stay Relaxed, Don't react. This also works when the front end slips a bit, or the back end squirms.

Happy Riding. Sims

http://www.facebook.com/photo.php?fbid=479606852816&set=a.479602142816.250146.577002816#!/photo.php?fbid=479606852816&set=a.479602142816.250146.577002816&pid=5722360&id=577002816
 

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I had the back end get really squirrely on me after I applied too much rear brake in a panic stop. Probably lucky I avoided a highside in rush-hour traffic- instead I eased off brakes and throttle, wiggled back and forth a lot, and moved the bike by sheer willpower into the space between the two cars ahead of me in either lane. Glad I was able to calm down a little and avoid extra input or I would have been a Rorschach test.
 

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My grandfather who was a CHP motor-cop way back when has told me to accelerate to get out of speed wobble, but does breaking work well for correcting wobble?
 

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Dylanj08, we seem to have two schools of thought here. One says relax & the bike will sort itself out & the other says you have to change speed (the quicker the better). I'm a firm believer in the latter.

See my post #4 above. Braking hard does work. It's very difficult to hold on to the bars and apply the front brake lever in a fullblown lock-to-lock tankslapper, but it does work! Because the f/wheel is oscillating from side to side you haven't got the same amount of grip as per normal at that given speed, so you shouldn't hit the brakes too hard in a tankslapper.... It's not easy because you feel you want to squeeze that lever as hard as you can, but that would be a recipe for disaster.
 

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This happened to me today. I got the wobble, let up on the grip, and the bike corrected itself.

Scared the **** out of me though....
 

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My tank slapper was on my old KZ. That thing would put the fear of BOB in an atheist.
Middle of passing a slow car (aren't they all) bike picked up a wobble. It had done this a million times, but this time the wobble went to a weave then full on tank slapper. Dents on both sides of the tank to prove it. Couldn't hold on, couldn't steer, just sat there gripping the tank with my legs. Managed to fanagle the bike into the grass by weighting the left peg and avoided the on coming traffic. it slowed on its own and stopped the slapper. Scared the poop out of me. Hitting the brakes are the worst things to do. It just adds to the problem.

The people who say "just accelerate through it" are out of their damned minds. May work on a car, but not a bike.
 

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I had a CBX750 as my second bike, and it went into tank slapping mode a few times. The first few times it did it I tried to stop it by controlling the handlebars - but this just made the problem worse. Later I found that pushing against both handlebars at the same time with light pressure reduced the slapping the quickest. I guess pushing against both bars acts like a damper, maybe it also had something to do with putting weight back over the front end as described in an earlier post.

After a while I discovered that the front forks on that bike had been bent rearwards slightly by a previous owner. After I replaced them it misbehaved much less often.
 

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Essentially, the cause of the tank-slapper is the front tyre bouncing on the ground, throwing itself back and forth. Therefore, the best way to stop it, and also the coolest, is to pop a massive wheelie, getting your front tyre off the ground and zipping along on the rear tyre. And don't forget, the best way to end a massive wheelie is with an equally massive stoppie.

Fact.
 

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My tank slapper was on my old KZ. That thing would put the fear of BOB in an atheist.
Middle of passing a slow car (aren't they all) bike picked up a wobble. It had done this a million times, but this time the wobble went to a weave then full on tank slapper. Dents on both sides of the tank to prove it. Couldn't hold on, couldn't steer, just sat there gripping the tank with my legs.
I'd ask anybody interested in this very unsavoury topic to read and re-read that again.

What kubbie is describing is a true tank slapper. Anything that you can correct yourself with handlebar wrangling/pressure is merely a speed wobble in my view. The two are light years apart :eek:!

However, I still maintain that hard acceleration or hard braking will end a full bore tank slapper, but as I posted previously to do it on the brakes is a really big cajones hairy experience!

Just for the record, my worst tank slappers were on a Honda CB900FA and on a Ducati 900SS bevelhead (the horn button scratched the Ducati tank transfer- at rest there was > 1/4" clearance at full lock, so it just shows how much the forces generated by a full on tank slapper bend and distort the frame, forks & tyres....)
 

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In a tank slapper the bike is trying rid itself of a handling problem, the rider. The bike will right itself if you move your weight forward and have virtually no input in the bars, and a very light grip. A motorcycle is a large gyro, and will right itself.
VERY well put! :)
 

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I am not so sure about a massive wheelie, but a slight one has worked. The problem of course is that you have to make sure you have everything lined up before the front touches down again, or you are right back into a slapper. After all, that is what started it in the first place.

One thing to remember if you do manage to get a tank slapper under control is to check your brakes before you need them. All that shaking around can move the pads away from the disks, so you could need an extra squeeze to get full brake pressure.
 
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