Tank slappers.? What causes them & how to save from them?

[tranquilride]

This is something Ive not experienced, and hopefully never will. :|
http://www.youtube.com/watch?v=auDoj_aH524&NR=1

From reading some of the comments, it sounds like the steering can suddenly jerk around spastically like that sometimes out of the blue? Being caused from coming down after doing a wheelie makes sense to me. But can they happen from other ways of just normal riding where the bike just goes awry?

Can anyone offer suggestions on saving from crashing if something like that occurs? Personal experiences with that type of riding unpleasantry?

 

[Hellfire]

I get a slight tank slapper when i get on the throttle coming out of a turn when riding hard out of a turn or i find a dip in a turn...its kind of werid at first, but im used to it now. I keep on the gas and keep my weight off the handle bars and i work on regaining control of the bars...that guy was pretty much screwed, unlocked his legs off the tank and his feet came off the pegs...

 

[209manny]

don't believe the comments on youtube most people there don't know jack shit.

from my personal experiences I never had a full on tank slapper but almost had one when I landed the front wheel a bit crooked after going over a hill what i did was ease on the handlebars and it corrected itself.

sometimes I would get a little wobble during quick acceleration but it would go away quick, I think that it is called head shake

 

[ScottRNelson]

These first two responses by Hellfire and 209manny are talking about headshake, not a tankslapper. Headshake is fairly common and usually not something to be feared. The guy in the video landed a wheelie a bit crooked, which caused his tankslapper. Do you really need to be told not to do high speed wheelies and land them with the tire pointed to the side?

The classic tankslapper video is the one of the black bike at the Isle of Man TT race. Sorry about the lame music they put on this version, but it was the only one I could find on short notice:
http://www.youtube.com/watch?v=C4KbGuQDYWo

On October 4th of 2003, I had a tankslapper just like that. The bike even went down on the right side, just like that, except that it slid off of the left side of the road into a ditch instead of off to the right to hit a curb. The bike was totaled, of course, and I ended up with a broken left hand.

In my case, the cause was hitting a cattle guard at 60-70 mph while in a very slight turn. The bump on the far side of that cattle guard was enough to bounce the front wheel off of the ground an inch or two and since I wasn't quite going straight, when the front wheel regained traction it was a bit crooked and it was instant tankslapper. I had just enough time to recognize that I wasn't going to be able to save it, then I was sliding down the road on my face. Good thing I had a full-face helmet on.

I'm certain that if the Ducati Monster I was riding had had a steering damper it wouldn't have gone into a tank slapper and I only would have experienced minor headshake. A steering damper is the best insurance against tankslappers.

I've also noticed a tendency to more headshake, potentially leading to a tankslapper, while accelerating, usually uphill, on a bumpy curve. I've heard of a few happening while passing cars for example.

A lot of people have theories about giving it more gas or otherwise doing something to change the amount of weight on each tire, but in a true tankslapper, there isn't much you can do once you've reached that point. Theoretically, if you could let go of the bars without falling off of the bike, the steering geometry of the motorcycle might be able to recover, but that's pretty unlikely to happen.

Tankslappers are rather violent and quite unpleasant. The best insurance is a good steering damper. That, and don't let the front wheel get off of the ground at speed either intentionally (wheelies) or accidentally (bumps while accelerating).

 

[HondaFreak]

I have experienced this, not fun. Didn't come off the bike even though I was going roughly 70 mph.
Low tire pressure (my front tire was under pressure)
Un-even road surface (I was getting on 85 South from 280 South, there's a lip or roll at the begging of the merge)
Too much pressure on the front handle bars and too tense. ( I was on a long ride and was tired, I was tense. V4 pointed that one out to me, Hi V4)

I got out of it by letting up on the throttle, sitting up, and taking a deep breath. So releasing the throttle and putting my weight more towards the middle/rear of the bike stopped the oscillations.

Christian

 

[Stormdragon]

From reading some of the comments, it sounds like the steering can suddenly jerk around spastically like that sometimes out of the blue? Being caused from coming down after doing a wheelie makes sense to me. But can they happen from other ways of just normal riding where the bike just goes awry?

The only time the steering's going to suddenly, out of the blue, jerk around spastically, is when you hit a deer.

Just to add to ScottRNelsons nice explanation, you can also get headshake from dimpled steering bearings. Trying to do a fast sweeper with the bearings juuust out of the dimple will make the bearings try to keep falling back into the divot, producing a nice high speed wobble. Quite the rush at 125MPH.

 

[Climber]

Here is one way to minimize the effects:

I've had a couple good tank slappers, one from accelerating too hard around another vehicle in an intersection across a patchy surface, another from accelerating too hard on some old (too old before install) dunlops while leaned over. Not fun in either case but didn't go down.

 

[aciurczak]

If your only bike is the one listed in your profile, you have nothing to worry about. A Nighthawk will not go into a tankslapper, ever. Sportbikes are generally more susceptible to these as their forks are much closer to vertical (less rake), so they can turn a bit quicker and feel more nimble at high speeds than other types of bikes It's why all of the literbikes and even most of the 600's are now coming with steering dampers right from the factory.

I had a pretty terrible one on an '05 R6 accelerating hard on a bumpy road; I came out of it by letting off all pressure on the bars and basically waiting for it to work itself out. It did so, and luckily before it went off the road. I put a steering damper on it the next week.

 

[Momo-san]

Looked like the guy in the first vid. just kept driving!

 

[Silence]

Relatively recent experience: 680 southbound right after the bridge, there's a left-hand turn and in lane 1 there used to be a series of pot-holes where the top layer of asphalt had been worn away (they may still be there). I managed to hit them in just the right way with the very edge of my tire as I was accelerating through the turn and caused a nice tankslapper. Smashed my hands into my tank, made me go three lanes wide and scared the bejeezus out of the SUV that was following me in lane 2. Oh yeah, it scared the bejeezus out of me too, it was the first time in ages that I actually thought I might go down and wouldn't have a say in the matter.

I've heard people say, "Just ride it through" "Get on the throttle" but I've also found literature that says you're supposed to put weight back onto the front end to re-establish grip and stabilize itself. The common theme seems to be to not fight the steering however. Since the tankslapper was so violent, killing the throttle was a decision that my bike made for me (it slipped out of my hands and I had to grab it again) and I wouldn't have been able to fight the steering even if I wanted to.

 

[Lucky13xx]

Lock your arms up, close your eyes and panic That usually saves me.laughing












Just kiddin, steering damper shift your weight back and stay on the gas

 

[xgambit]

what you call tank-slappers, i call lane splitting on the bay bridge.

 

[subsoniic]

i have an 05 r6, i remember b4 my damper the front end would get so light and get mild headshakes from jammin thru 1st gear, the front end was just to nervous for my taste, so i decided to pick up the scotts damper, man its such a great lil gem. I still however get mild headshakes here n there, several of them were very violent, i think without the damper i would have experienced the tank slappers. Some people say 'oh i dont need it, just get ur suspension dialed in correctly' That is a good thing, and i've done that, But i dont think it can help with the headshakes due to uneven road condition, and how much power u have on ur bike, i may be wrong, but over all no regrets on my end.

 

[ThinkFast]

Hang on like mad...http://www.youtube.com/watch?v=p509Ue_MlKk

I had a nearly identical experience to the guy in this video, minus landing on the side of the bike - I held on tight and ended up back in the saddle (carousel, Road America, ~80-90mph, hit coolant, set up a high side). Back in the pits noticed a white paint streak on my windscreen and scuff on the shoulder of my leathers...there's only one way that could've happened (I didn't realize it as it happened - probably had my eyes closed preparing for hard landing). I happened to have seen this video a month or two prior to my incident, and I swear it's what made me hang on so tight.

 

[Alexey]

This stuff is pretty poorly understood by a lot of people. As has been noted, front wheel oscillations are not all the same in nature. What folks don't realize is just how different they are. Here's a relevant section of a very good Wikipedia article on the subject of bicycle and motorcycle dynamics.

Simple front wheel self-correction tends to be fairly harmless. You'll typically see it, as has been said, when the front is unweighted under acceleration or steep ascends with uneven forces on the front tire (partially leaned over on a bumpy surface). In such circumstances, simply avoid the death grip on the bars. Also, keeping your bike in good mechanical shape can go a long way to avoid or keep these in check. So make sure your tire pressure is correct, tires themselves in good shape and are balanced on the rim, steering head bearings are in good shape and correctly tightened, wheel bearings are good, rotors aren't warped, etc. Then keep a nice loose grip on the bars and don't panic if you feel a bit of movement. As has been said, chassis geometry is important too (trail, not just rake). A Nighthawk would be very difficult to serious upset. I recall getting a serious tankslapper my first time at Thunderhill on my first race lap coming over the hill in T9. I thought I was a goner for sure, but managed to ride it out. Subsequently, I was more conscious of line, acceleration and steering inputs in that spot and I was able to settle into a pace, where I was getting just a bit of a wiggle from the bars, but it didn't get out of control. When I got home, I realized my steering head bearings were too loose and later on I could run the bike wide open with the same setting without any problems.

Then there's things like harmonic oscillations of the front and rear wheels. What's happening may feel like headshake gone wrong, but actually the entire bike is oscillating about the steering head axis. That's what can throw the rider off the bike. There's very little that can be done. If possible, changing the speed is not a bad idea. But the truth is those things come on quite quickly and violently.

 

[Burning1]

A lot of people have theories about giving it more gas or otherwise doing something to change the amount of weight on each tire, but in a true tankslapper, there isn't much you can do once you've reached that point. Theoretically, if you could let go of the bars without falling off of the bike, the steering geometry of the motorcycle might be able to recover, but that's pretty unlikely to happen.

I doubt it. To the best of my knowledge, a tank slapper is a harmonic resonance in the front end, where the steering geometry over-corrects from one side to the other. The self correcting nature of the motorcycle is exactly what produces a tank slapper.

If I recall correctly, the theory behind accelerating is that it changes the resonance frequency of the front end, and disrupts the tank slapper.

To the OP:

I've produced a near tank slapper by aggressively accelerating while applying steering input over the bots-dots. I'm pretty sure my shocks were mis-tuned as well. The lightened front end and the bump caused the tire to leave the pavement. Applying steering input caused the tire to point well away from straight ahead. The forces of caster (trail) at the front end caused a rapid over-correction, that resulted in a moderate tank slapper.

Since I have a steering damper, it was quickly dissipated.

As I recall, the tank slapper won't generally cause the bike to crash unless it becomes so violent that the steering head hits the steering stops (this is where a tank slapper gets it's name.) If the head hits the stops, the front tire can tuck under, causing a high-side.

 

[ScottRNelson]

As I recall, the tank slapper won't generally cause the bike to crash unless it becomes so violent that the steering head hits the steering stops (this is where a tank slapper gets it's name.) If the head hits the stops, the front tire can tuck under, causing a high-side.

And I say it isn't a tankslapper if the bars aren't going full lock. Wiggling bars is headshake and something that you can usually recover from. It has to be actually slapping the tank before you can call it a tankslapper. (At least, that's my opinion.)

And I can't figure out what the "I doubt it" is supposed to go with in the paragraph of mine that you quoted. There are four or five things in there you could have disagreed with. If you can clarify what part of it you didn't like, it might be worth discussing this further.

Overall, I feel that this has been an informative thread. Let's hope none of you get to experience a true tankslapper in person.

 

[mhpcto]

I've only had one real tank-slapper and that was when I rode my RGV250 (had two at the time, one for the track, one to commute on). That bike, being as light as it is, could get real flighty when it hit the power band but was easy to control with body english.

I hit a deep, long (20 yards or so) crack in the tarmac - so deep and just the right width that I basically got stuck in it. Naturally, that crack was pretty wavy and uneven and the bike would basically follow it. Just like a head-shake but it was really a bike-shake. As exciting as that was, the finale came when I hit the end of the crack and bounced out of it completely out of shape. Well, a 280 pound bike plus rider goes airborne a lot easier than a 600 pound harley with a couple of bad ass mamas on it.

The airborne portion of the ensuing trajectory was ok but I got deductions for the landing. Tank-slapper from hell that crushed one of my thumbs. It wasn't a quick one either. Seemed to go on forever - until I let go of the bars getting ready to voluntarily depart this bucking beast - it immediately settled. I pulled over and got off. At that point I was the one shaking.

Steering damper on all my bikes ever since.

 

[Burning1]

And I say it isn't a tankslapper if the bars aren't going full lock. Wiggling bars is headshake and something that you can usually recover from. It has to be actually slapping the tank before you can call it a tankslapper. (At least, that's my opinion.)

And I can't figure out what the "I doubt it" is supposed to go with in the paragraph of mine that you quoted. There are four or five things in there you could have disagreed with. If you can clarify what part of it you didn't like, it might be worth discussing this further.

Overall, I feel that this has been an informative thread. Let's hope none of you get to experience a true tankslapper in person.

"I doubt it" was referring to taking your hands off the bars and having the motorcycle recover on it's own. In a lot of the tank slapper videos I've seen, the oscillation of the front end increases as the tank slapper progresses.

I'm sure you can take your hands off and recover from a wobble, or headshake though.

 

[Coffae]

In the first video, the guy having the tank slapper looked like he was trying to control the bike. His input of resisting or pushing back on the gyrating handlebars may have contributed to the problem as if he was actually out of sync with the handlebar swapping, he accentuated it.

As many have stated, let the gyroscopic effect of the bike do its thing and try your best not to fight it. I agree with the front to back resonence theory as well. Changing speeds may be corrective if you can do so with light input to the throttle.