Tank slapper explained ! - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 27 (permalink) Old 07-02-2008, 04:51 AM Thread Starter
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Tank slapper explained !

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.

Ride on !

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post #2 of 27 (permalink) Old 07-05-2008, 12:43 PM
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post #3 of 27 (permalink) Old 11-06-2009, 11:56 PM
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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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post #4 of 27 (permalink) Old 04-13-2010, 11:05 AM
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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 .


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post #5 of 27 (permalink) Old 04-14-2010, 12:05 PM
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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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post #6 of 27 (permalink) Old 12-09-2010, 07:36 PM
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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


Last edited by Sims; 12-09-2010 at 07:38 PM. Reason: Photo not working, changed to link
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post #7 of 27 (permalink) Old 12-09-2010, 08:04 PM
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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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post #8 of 27 (permalink) Old 06-01-2011, 03:04 AM
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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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post #9 of 27 (permalink) Old 06-02-2011, 07:12 AM
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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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post #10 of 27 (permalink) Old 10-28-2011, 11:00 AM
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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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