50 kp/h tank slapper

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SkyRider said:
couple of website's "anecdotal' claims doesn't make it fact. you can ask any track rider on gtam and they can answer you.
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Wow, nice logic bomb there pal... dismiss published data as anecdotal by referencing more anecdotes :rolleyes: Did you actually read the info? Here, I'll make it easy for ya' sport:

Imperial College of Science - Motorcycle Steering Oscillations due to Road Profiling
Imperial College of Science - On steering wobble oscillations of motorcycles

"The effect of changes in the rider’s upper body mass on the transfer function that maps road vertical displacement to the steering angle are studied in Fig. 16. As suggested in f.18, an increase in the rider’s upper body mass by 20 kg (44.1 lbs) reduces this gain peak by approximately 8 dB. In the same way, a reduction of the rider’s upper body mass by 20 kg (44.1 lbs) increases the peak gain by approximately 7 dB."

"The response of the rider to a potential accident situation will primarily be to stiffen both arms and torso, which actions only marginally stabilize the wobble mode. The fundamental difficulty for the rider is that the available stabilizing action is likely to be insufficient to counter a developing problem, especially one started by some unfriendly excitation, in which a relatively large amplitude develops quickly."
 
[video=youtube_share;53f05G9NqKI]http://youtu.be/53f05G9NqKI[/video]
 
kiwi said:
Huh? That's not a tank slapper..is it???
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Nope, just a wee bit of fishtailing. Traction control actually would have reduced/prevented that.
 
hahaha i read it now. but it's just a research paper. thousands of research papers get pumped out of a university every semester. the author(s) alone referenced some anecdotal data.

i skimmed thru it and it never really addressed anything related to how tank slappers occur. and they used "simulator". is this simulator accurate?

look at this vid http://www.youtube.com/watch?v=GvHtChodNk0
at 0:11 tank slapper starts. if you look at the tach. rpm is close to redline, then is when the front wheel lifts up, then rider upshifts, you will see the tach dip a little. when rider shifts gear the bike touches down. but the front wheel was a little crooked. hence causing the tank slapper. it doesn't take a research paper to figure out that touching down a bike with front wheel crooked is bad news.

i get that there may be many other variants of a tank slapper. but this particular one is related to what OP experienced.

also read what the video poster wrote on this video page. luck did also play a big role.

basically you did a quick google and take the first "research paper" you see as gospel. immediately reject all other possibilities. i recommend this link someone posted in off topic http://yourlogicalfallacyis.com/

here is another vid. you can clearly see the reason the tank slapper started was because he landed his wheelie with front wheel crooked

http://www.youtube.com/watch?v=HtjQ4SK4GXk

so to summarize, yeah the research paper you quoted had equations and lots of words. but a picture is worth a thousand words, a video is worth 30 thousand words (if the video is 30 fps).

Acadian1974 said:
Wow, nice logic bomb there pal... dismiss published data as anecdotal by referencing more anecdotes :rolleyes: Did you actually read the info? Here, I'll make it easy for ya' sport:

Imperial College of Science - Motorcycle Steering Oscillations due to Road Profiling
Imperial College of Science - On steering wobble oscillations of motorcycles

"The effect of changes in the rider’s upper body mass on the transfer function that maps road vertical displacement to the steering angle are studied in Fig. 16. As suggested in f.18, an increase in the rider’s upper body mass by 20 kg (44.1 lbs) reduces this gain peak by approximately 8 dB. In the same way, a reduction of the rider’s upper body mass by 20 kg (44.1 lbs) increases the peak gain by approximately 7 dB."

"The response of the rider to a potential accident situation will primarily be to stiffen both arms and torso, which actions only marginally stabilize the wobble mode. The fundamental difficulty for the rider is that the available stabilizing action is likely to be insufficient to counter a developing problem, especially one started by some unfriendly excitation, in which a relatively large amplitude develops quickly."
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-You can still have tank slapper with a damper, at-least i'm sure i did over rough pavement and holding on too tight & more recently on the highway tiny little wobbles. Damper mitigates but doesn't prevent them as far as i know. Funny thread though: interesting how Riding is as much science as art i agree with throttle to get out i'll leave bringing weight forward to researchers.
 
While we're on the topic of Steering Dampers...
I had lots of little tank-slappers, and one very memorable, back in the day (beginning with CB750K3 in the 1970s).
I installed an aftermarket hydraulic steering damper on that bike, 35 years ago.
Still have a little divot carved out of my left leg, where it thrashed against the end of the SOHC motor!
And I actually had a passenger on board; kept it up (by pushing forward on both handlebars) and we eventually rolled to a stop.
Was he okay? Yeah, he guessed so...
Then we noticed: he had only one shoe on! The brutal wobble had extracted his other shoe.
Didn't realize (at the time) how close I had come to killing us both.

Anyway, Steering Dampers have a problem.
That is: when going fast, your handlebars don't turn - you change direction via "countersteering".
In this situation, the adjustable damper needs to be full-stiff.
Then eventually, you're going to slow down which is typically required before you stop.
Any slow-speed maneuver or turn and you will fall over (or maybe even crash) because the damper is way too stiff!
You have to not only adjust the damper, but remember to adjust the damper, heheh...
This becomes a giant product-liability issue on today's bikes with OEM Steering Dampers.
All the OEM dampers you see (ie. Ohlins on ZX-10R and R1) are neutered so they don't go stiff.
This is not the same damper as the aftermarket Ohlins you can buy for about $700 bucks.
Specifically, the damper rod has been modified to severely reduce the adjustability of the damper.
You can therefore click it from extreme to extreme, and there's really not much difference.

As usual, Honda is the first one to get it right: the Electronic Steering Damper that changes stiffness based on the motorcycle speed.
Sure, maybe costs more - but it works!
And you won't see n00bies taking delivery of brand-new bikes falling over at parking-lot speeds (an OEM's worst nightmare).
The best cure for wobbles is prevention! Be aware...
Today's quick-steering nervous-handling bikes will wobble more readily.
As "trail" (the front wheel's self-centering tendency) is reduced, for nimble handling and quick direction change on the racetrack, this is what happens.
Once again, a SS bike is not the hot setup on the busted up streets in the real world...
Regards
 
casacrow said:
I believe most of these slappers are likely caused by too tight of a grip on the bars. They are there to receive your inputs, not to hold you up.
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Actually I had a few high speed wobbles all from the on-ramp. This when I was new to riding. The first one I wobbled so much I was veering towards the left concrete barrier and could only hope and pray the bike settles itself which it did by letting go of the throttle and not trying to fight the steering.

I learned that I was too light on the handlebars which is why it happened few times so since I've gone heavy on the handlebars when leaning into a turn the wobble hasn't happened since.
 
Y'all can test it out for yourself.

Get up to speed in top gear, let go of the bars, and smack your left bar really hard. Use a sharp blow, not a push.

This will start head shake. Don't touch the bars and watch the bike quickly settle.

A properly maintained and functioning bike will correct itself rather quickly with no additional rider input. This feature comes built into the bikes free of charge.

If you attempt to stop this shake by strong arming the bars, you may cause the shake to be transferred through you, to the rear of the bike. That's when the fun of a true stop to stop tank slapper can begin.
 
Yamaha also has the electronic damper, have for a few years. It works ok but still needs to be upgraded for track use just like all the oem units.
 
True it corrects itself but who has personally tried ; whacking the bar in top gear?
 
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VicRR said:
True it corrects itself but who has personally tried ; whacking the bar in top gear?
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It would be unwise to say the least, even for the sake of education to put yourself in that position.

I have had many speed wabbles, usually well above 150 and they have never been "tank slappers". I could always pull the clutch and keep my hands on the bars until the wabble settled. Scarry, but not too bad.

This was totally different, going 50 is pretty slow as was the frequency of the shake, but extreme as all hell, from lock to lock and hard. No way I could hang on or grab the clutch, I'm just lucky that my hand accidentally touched the throttle enough to bring me out of it.

Ps, as the bike slowed it did seem the slapping was becoming more violent and hard, even though the speed of the shake slowed. I assume this is why the sudden throttle blip creating the speed burst made it stop.

This is hugely scarry, nothing like a high speed wabble, please do not ever initiate it. I'm sure it will happen on it's own down the line.
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