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Ever get into a Tank Slapper? Head shake? (vote on as many that fits)

  • I never had a Tank Slapper

    Votes: 34 63.0%
  • I had a Tank Slapper at low speed (54 MPH or slower) and pulled out of it OK.

    Votes: 10 18.5%
  • I had a Tank Slapper at low speed (54 MPH or lower) and could not pull out and crashed.

    Votes: 2 3.7%
  • I had a Tank Slapper at high speed (55 to 70 MPH) and pulled out of it OK.

    Votes: 8 14.8%
  • I had a Tank Slapper at high speed (55 to 70 MPH) and could not pull out and crashed.

    Votes: 0 0.0%
  • I had a Tank Slapper at VERY high speed (71 and above) and pulled out of it OK.

    Votes: 3 5.6%
  • I has a Tank Slapper at VERY high speed (71 and above) and could not pull out and crashed.

    Votes: 2 3.7%

  • Total voters
    54
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Discussion Starter #1 (Edited)
If you have had a Tank Slapper then answer please. As with all polls there will not be an exact answer so do as best as you can.

If you do not know what a tank slapper is, it is when the front tire is skipping on the ground and the handle bars are going back and forth to the extent they may hit the tank if you had a tank. Most viewing on here do not have a tank between the knees.
 

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No, never had one & don't care to find out how it feels to have one. ;)
 

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In my many years of riding that is one thing I have never experienced. I've had minor shaking of the bars but never a full fledged tank slapper. Like Desert Rat I don't care to either.
 

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Discussion Starter #4
Yeah, like Mike and Craig both have said they have not gotten into one and I expect the poll to show that through out.

I have had 6 real tank slappers but many many more slight head shakes. Head shakes are usually caused by loose head bearings preload or tire conditions like cupping.

Tank slappers commonly are caused by poor designed or maintained front suspension, poor tire choice/design/maintenance, road conditions or debris.
 

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Yeah, like Mike and Craig both have said they have not gotten into one and I expect the poll to show that through out.

I have had 6 real tank slappers but many many more slight head shakes. Head shakes are usually caused by loose head bearings preload or tire conditions like cupping.

Tank slappers commonly are caused by poor designed or maintained front suspension, poor tire choice/design/maintenance, road conditions or debris.
First, I am no engineer or scientist. 6 tank slappers seem awful high for one guy. I just had some thoughts that I want to share. When I was young I used to go to the drag strip with my Kawasaki 500 tri-star. It was common to let air out of the back tire to get more tread on the ground. This is before the use of square or car tires, eventually slicks. At high speeds, 80 and above head shakes would happen. Back then some bike were made with a wheel that could tighten the headset. The problem was if too tight the bike would drift left or right and hard to control at 120+ mph. Then. lateral steering dampeners showed up. After the races we would put the proper air pressure back in and have no head shake problems when violating the speed limit on the streets. I can't help thinking that the use of a car tire with lower pressure might enhance front end oscillation at any speed. I DO NOT condemn nor advocate the use of ct's. I bought an extra rim to put a car tire on and do my own experiment. After Dave's accident, this poll, and my own experiences, I am having second thoughts on car tires. Note, I now have a custom tuned front end, I do know the dangers of a weak steering and front end suspension.
 

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I have never had a tank slapper. Not interested in having one either. I will trust the stories from those who have had one and lived to tell the story. I did have a bike that liked to do a head shake now and then, cured the problem by dropping the triple trees on the front tubes thereby changing the geometry of the front end on the bike. Never really trusted that bike afterwards.

Doug
 

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Discussion Starter #8 (Edited)
First, I am no engineer or scientist. 6 tank slappers seem awful high for one guy.<<<SNIP>>>
In over 1 million miles riding powered 2 wheelers mostly as a SQUID, I have had many different issues on bikes that a rider that has done 12,000 miles in their life never will encounter. Of my 6 real Tank Slappers, 1 ended as a crash. In all other bikes I cured the issues by redoing the front suspension, adding a fork brace and a dampening device.

<<<SNIP>>>I DO NOT condemn nor advocate the use of ct's. I bought an extra rim to put a car tire on and do my own experiment. After Dave's accident, this poll, and my own experiences, I am having second thoughts on car tires. Note, I now have a custom tuned front end, I do know the dangers of a weak steering and front end suspension.
Don, I am running a wide flat car tire at 44 PSI. thats how I like it.

I have also had rear tire shake in the past and kind of know when the tail is shaking the dog. :D I too ran Drag only Harleys on 10-20% Nitromethane mix in the 70's and 80's with "The Big Slick Daddy". I would carry the front wheel past the 60 foot marker and when that tire touched down it was almost always a head shake. Could my rear tire have "Helped" in this tank slapper crash? Sure, but I think the discarded tire debris stuck in my front end was 99 and 44/100th's the real issue.
 

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I had a tank slapper on the Burgman.

Stolen car rammed me from the side, had a wild rodeo ride but the bike recovered itself eventually. I kept my arms loose, tried to buffer the extremes only and let the geometry do its stuff.

A true tank slapper is due to the geometry over-correcting and setting up an increasing oscillation.

The rear tyre can have a part to play - the height at the back alters the castor angle at the front and alter the stability.
Having a car tyre on the back also causes the rear ride height to fluctuate in the opposite direction to normal and change the stabilising rake angle. It will also make the contact patch move laterally at a different rate to the front as well as "fall off" the corners as the bike returns to neutral.

The rake and wheelbase are the main factors in stability.
It usually takes quite an impact to cause a slapper on a Burgman. It is much more likely to effect a short wheelbase, high power bike with a quick turn in due to its front rear geometry and rear diameter. With the power on it only takes a small deflection to set up the oscillation.
 

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http://burgmanusa.com/forums/20-safety-tips-ideas/91361-dreaded-tank-slap.html

I started a thread on this a while back. Perhaps it deserves a bump for the new members.
I have gotten to have this issue too. For me the thread Liam included helped me to know how to handle a tank slapper. For me it was based on front end adjustments and weird rear tire issues.

May all who have never encountered be lucky and avoid it. I do advise giving that thread a read and learn how to cope with it just in case.

John
 

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Discussion Starter #12
56.25% of 32 voters have never had one, good and about what I expected. And of the 24 voters that have, only 3 crashed, good too, unless you were one of the 3. :twisted:

Like said above, hope you never get into one but you should study on how to save a crash out of one.

Besides myself, who was the other crash in the VERY high speed above 71 MPH? Your story please.
 

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Rigidity of the rear tyre carcass and how it displaces also affects how wobbles develop - another reason the structure of car tyres is different to bike tyres
(Forgot to mention it in earlier post)

Stability at speed comes from the bikes geometry, not gyroscopic effects as described on lots of sites.
 

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Discussion Starter #14
Ok, I will ask that we do not turn this into a Darkside war. A few have posted their opinons and I thank you for it. But it is about as good as saying the awful front suspension is junk over and over and over.

In 5 of my 6 tank slappers, they all were on OEM spec Motorcycle Tires for the bike, ether Dunlops or Conti's. So that 20% of my slappers on Car tires seems big but it is not.
 

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Sorry if it sounded like trying to start a war, it was intended purely as data that the public doesn't usually have access to and has to guess at.

I've studied and worked in vehicle dynamics for many years and thought it might be interesting or useful to hear from the designer and kinematics side of things.

I'll butt out
 

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In over 1 million miles riding powered 2 wheelers mostly as a SQUID, I have had many different issues on bikes that a rider that has done 12,000 miles in their life never will encounter. Of my 6 real Tank Slappers, 1 ended as a crash. In all other bikes I cured the issues by redoing the front suspension, adding a fork brace and a dampening device.



Don, I am running a wide flat car tire at 44 PSI. thats how I like it.

I have also had rear tire shake in the past and kind of know when the tail is shaking the dog. :D I too ran Drag only Harleys on 10-20% Nitromethane mix in the 70's and 80's with "The Big Slick Daddy". I would carry the front wheel past the 60 foot marker and when that tire touched down it was almost always a head shake. Could my rear tire have "Helped" in this tank slapper crash? Sure, but I think the discarded tire debris stuck in my front end was 99 and 44/100th's the real issue.
I was never that brave to race a nitro bike. Had friends who did and all 2 of them got sponsored. Track stories we both probably have quite a few.:D Anyway, I agree with you 100% on what caused your accident. I just hope that you are covered with your insurance. I called mine this morning to see if I was covered if road flotsam or any vehicle hitting junk on the road were to cause me to crash. The agent thought I was but not clear on the details and would get back to me. I think she forgot me and will have to call them again.
 

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I have never had one on a motorized bike but have had them on bicycles. The few I had ended up with me in the dirt.
 

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I had one episode of a tank slapper happen to me. I had a 1983 Yamaha XC-180 scooter and was riding on a secondary (back) road at around 40-50 MPH. A dog ran out beside me and barked very loudly so that scared the devil out of me. I must have locked up the front brake and all of a sudden, bang-bang-bang the front wheel goes. I did not run off the road and stopped 100 or so feet after the dog ran back to his home. I sat there along the side of the road wondering what just happened. The roadway was a coarse asphalt, no pot holes or imperfections that I could see. I must have locked up the front brake instead of s-q-u-e-e-z-i-n=g it on. I'll tell you, its an experience I wish to NEVER see or feel again. Joe...
 
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