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Tankslap recovery


SWing'R

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Can't remember where it was but there was a recent post that ended up talking about tankslapping recovery

technics and there was some debate on the right or wrong way to recover.

Well, I am currently taking the MSF BRC (had the classroom session last night) and one of the things mentioned

is what to do in the event of a "wobble or weave" (tankslap being the wobble) and the correct answer for both

scenarios (according to the MSF) is to firmly grip the handlebars without locking your arms and to deaccelerate,

NOT accelerate as someone was mentioning in the other thread.

Just thought I'd pass this along.

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Tank slap is a frequency based oscillation. It is dependent on the vehicle speed for the frequency of oscillation.. It can happen from a flat front tire (or flat rear tire), suspension design or problems, mechanical failures, or interaction between the tire and the pavement.

Both increasing and decreasing the vehicle speed can make the oscillation stop, but not always, not every time. But most oscillation would be recognized as speed increased, making it much more likely that speed should be decreased in order to get rid of it. Not to mention that your survival rate goes up as velocity goes down.

The point is... You do have to fight the oscillations till it's gone. I'd much rather be slapped at a slower rate of 30 times a minute, than 120+ times a minute. So I wouldn't try to accelerate out of it. Not to mention that you still have to ride the bike, stay on the road, avoid other vehicles and obstacles, etc.

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tankslapper is not a wobble. your BRC class won't cover anything but the basics of riding and low speed manuvering.

true tankslappr is when the bike's bars are shaking and cannot be controlled

Taken from page 43 of the MSF BRC book Section IV...

"...possibly strong shaking of the handlebar" Sounds like a tankslap to me.

wobble.jpg

Edited by SWing'R
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:lol:

jesus christ man. I don't even have the patience to reply if you're going to copy and paste some shit out of a motorcycle SAFETY class

What. I'm just sayin.

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first of all, it will usually stop before you think about what to do or realize it's happening.

a motorcycle as long as it's moving will correct itself.

why? because the wheels act as a gyroscope. the faster they spin the more stable the bike becomes.

if it goes into a full side to side shake, more than likely no matter what you do, you are probably going to get bucked off. but the bike will keep going. unless of course you fall over with the bike by holding on to it.

as long as you have the room and don't fall off, it will stop.

there was a show about modern sportbikes called "speed on two wheels" on discovery (science) channel a few years ago and they demonstrated this by intentionally setting off a pretty violent one.

Edited by serpentracer
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Yeah I would like someone to demonstrate the brake in a tank slapper. I have been in 6 tank slappers in the last 8 years. The minor ones where scary the major ones where just a blur. On the big ones the bike is shaking so hard it knocks your legs out from the bike so they are dangling in the wind. Every tank slapper I have been I have powered out of. In the different articles I have read they have all said power out hopefully you have enough power or are in a low enough gear to pull all the weight off the front wheel which will stop it the quickest.

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Brakes never did me any good. Mostly made it worse. I just let it roll to a stop or till it stops, as best as can. Can still down shift. I agree with popping the throttle and clutch to unload the front wheel. It's worth a quick try. Some oscillations are so violent, using the hand controls are difficult or impossible.

I'm thinking there are a lot of variables. It's going to be whatever works.

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I've only had minor tank slappers. I've witnessed a major one. The guy in front of me hit the edge of a pot hole and he really couldn't do crap. Once he came out of it, he was still holding on and the bike kept going straight and on course. From the looks of how violent and quick his was, I don't think there is any way in hell that he could throttle or brake quick enough to do anything.

To combat this, I bought a damper. Haven't had an opportunity to test it out though, thank goodness.

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I don't know how so many of you have so many of these. I only have the normal wobble from cresting a hill or a small on the power wheelie coming back down.

I don't have a damper.

maybe you guys are doing something wrong? I just can't imagine what you might be doing to cause them so much besides pulling or putting all of your weight on the bars too much.

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Good question, tank slappers are supposed to be rare. If anyone had many on one bike, I'd say something is wrong with the suspension, setup, design, etc.

I've had three in 40 years. I don't remember any more than that.

One was slow speed oscillation on a freeway crossover ramp. It used all the pavement and wanted more. I had to fight that one and slow down. I was already going too fast. As best we could figure out, it was the dual calipers mounted on the front of the forks. When put on the rear of the forks, it didn't do that. We reversed the forks and calipers. They were on the front the first model year, and on the back of the fork all the other years.

edit: when I say slow oscillation, it was about 60cps, one per second. Just barely able to counter it with force.

Another was a flat front tire (blowout). It shook like no tomorrow, and took off across a 4 lane road (five with center turn lane), and back again, and repeated till it slowed down on it's own.

Tire design used to cause a steady tank slap on freeways. It was rib tires on freeway rain grooves. We called it the BMW disease. It varied with the speed. The tire designs were changed to avoid that. It could be ignored, but it was weird to flop around like that at a steady freeway speed. It definitely freaked out all the cagers. We all bought new front tires.

Little wobbles and shakes over crests of hills and such don't count. They will stop when that gyroscopic action settles back in.

I don't think I've ever had a killer tank slapper. I can do without that.

Edited by ReconRat
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It's tank slapper video time!

Ok, I looked through a batch of videos, and most were little wobbles.

Most were just headshake or momentary instability.

Here are two real tank slappers that resulted in crashes and injuries:

This is a tank slapper coming out of a turn:

http://www.youtube.com/watch?v=LZ1srcQMa_0&feature=related

This is a tank slapper coming down from a wheelie:

http://www.youtube.com/watch?v=YD6jruSIELA

Reading motorcycle stability. The tank slapper and/or a wobble is induced from a difference between the motion of the motorcycle based on the center of gravity of the motorcycle and the rider (inertia/momentum), and the procession (shake) of the front wheel as a gyroscope. Most problems are induced by a change in the motorcycle and rider's center of gravity while the front wheel is in the air or lightly loaded. That causes the gyroscopic front wheel to turn away from your line. Resulting in a violent shaking when it returns to the pavement. It means the bike is going one direction, and the wheel is going another direction. They then fight about it. Shaking both the front wheel and the motorcycle/rider.

Yes, a quick shift in rider position should get rid of the problem. By restoring the matching center of gravity, for what it's worth. Not likely to happen. That comes from a ton of experience.

No, unloading (accelerating) the front wheel again will not change the front wheel's gyroscopic procession.

Yes, unloading (accelerating) the front wheel again will stop minor headshake/tankslap (mostly your arms force the procession away at that time).

Yes, gripping the handlebars can dampen the procession out with the arm muscles. But procession is a large force, and it won't be easy.

Note that getting the feet off the pegs does not seem to help at all. It appears to make the problem worse. Moving the body around can help or hurt the center of gravity. The legs appear to flop at the rate of procession, making it worse. With that much shaking, looks better to hold still. Moving forward or aft would be the exception, in line with the center of gravity. And doing that, should change the bike's center of gravity a bit, and correspondingly, the procession of the front wheel, for better or worse.

tech stuff: headshake, wobble, and tankslap are very linked to the amount of trail. Changing ride height, suspension height, tire size or profile, rake, or fork offset, can all make the trail better or worse.

Sorry for the blah blah blah, I'm just a geek...

Edited by ReconRat
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Where the Fuck where all of you guys when I was preaching to the know it all choir of krzwhtman and company?... LOL

http://www.ohio-riders.com/showthread.php?t=28168&highlight=fast+bike+magazine

One of the few times i wished bad luck on someone... haven't heard from him since maybe my wish came true.

grow up kid

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