Tankslappers explained

[Nzpure]

had what could only be explained as a tank slapper experince under severe heavy braking on the busa scariest moment of my life!

[ducatilover]

I've had a few scary experiences when the Gixxer gets into a mild tankslapper, the worst was accelerating hard down a straight piece of road in 2nd gear and the front end started wobbling quite bad. Wasn't expecting that, especially considering the road was pretty smooth.

More rear bound damping or more front rebound would sort it?
In my head...or maybe your tyre pressures were out/you should put more weight on the front.

Or keep it on one wheel bro

[ducatilover]

had what could only be explained as a tank slapper experince under severe heavy braking on the busa scariest moment of my life!

I've had me a few, best way I found to avoid 'em is not to ride hard.

[R-Soul]

I agree with Ixion - this sounds like the exact opposite of what you should do. I agree with the definition of what a tankslapper is, but not their proposed rsponse.

First they explain that it is teh small "kick" that gets given to the pendulum in a granfather clock that keeps it swinging in harmonic fashion, and then they say that you should stiffen your arms? Stiffening your arms will GIVE the handlebars that additional kick that counters the DAMPING action of the forks.

I had an experience with a car that is quite a good analogy to this:
A rabbit jumped out onto the highway while I was glancing down. As I looked up, I saw it and jerked the steering wheel by reflex. the car swerved to the side, and I corrected, which made it swerve to the other side more violently, which I corrected again, to make it swerve ebven more violently back again, etc etc until the back stepped out and the car did a 360 on the motorway (luckily at night, so it was empty). I was told by an advanced driver afterwards that the car suspension is designed to self correct to a straight line, and it was my arm inputs on the steering wheel that were causing the over correction. Taking that analogy to the bike - similarly by trying to hold the bars firmly, you are not letting the forks 'self damp'. Holding the bars loosely may be a better option.

From an engineers perspective, you can interfere with the harmonics caused by a regular periodic force (the force of the road on tyre) being applied at a resonant frequency to cause resonance by:
1) removing or reducing the forces being applied (by lightening the front wheel to reduce the force being applied by the road to the tyre and letting natural fork damping do the rest- like Shaun said)
2) damping the actual movement (like with a steering damper)

I cant think of any more although the comment earlier about a bike going sweetly into a turn was interesting. Perhaps applying force to only one side of the bars will interfere destructively with the periodic forces of the road on the tyre? In this case, then perhaps swerving from one side of the road to the other might help? Can somebody try this and let us know if this works?



I can't think why back brake would help (except to slow the bike for it you do get thrown)? Perhaps by braking you are changing the frequency that the force of the road is acting on the tyre. If this is true, then I guess this would apply to both brakes then, except that with using the front brakes, the moving bars can cause damage to your arms. Also, if Shaun was accelerating while braking with the back brakes, then this would negate that effect. Any ideas?

*IDEA* By braking, you are loading up the front end, and making the suspension stiffer, thereby causing more damping. that may be why it helps.

I hit a block of wood in teh road the other day, the bike flew up into teh air and the front wheel landed skew, making the head shake similar to a tankslapper. I loosened my arms, and let them flap with the bars, instead of fighting the bars. It shook itself out rather quickly, and damped itself of its own accord, and I was able to stay in control (but my rims were muntered).

Remember seeing how many riders come off the bike in races, and the bike carries on riding down the road, perfectly balanced, after the rider is chucked off? This is because it is deisgned to stay upright and damp itself.

[ShAdOwDrAgOnS]

Not many bikes seem to have a rep for doing it nowadays. ZX10R without damper and CBR600RR are the only ones I've heard about that will if provoked.

I haven't experienced a tank slapper yet. At most a slight tail wiggle when coming out of an uneven corner while accelerating hard and slightly losing traction and a few times where the front lifts up completely and you end up completing the corner on the rear wheel only until you can set the front down gently.

So far I’ve found the CBR 600RR to be a very forgiving bike.

Anyone else had tank slappers on a CBR 600RR?

[eldog]

tankslappers explained ok

There seems to be lots of ways to get one, all basically from the same problem, front wheel, bike travel direction misalignment

In my case, I was a beginner, had only ridden the bike maybe 100ks, as going slow 70 in the wet.
Yes the bike did have bar end weights.
It had PR3 tyres which were nicely scrubbed in.
I had the bike going through a slight corner/bend in the road, It was vertical as I travelled 1/2way through the corner, hit big patch of wet tar bleed, rear slid out along way, I twisted on the bars (like in a car-silly me) and it was on, never thought my arms could move so fast.

Since I was a beginner when I had mine and I hadnt read this thread. Since reading it, i am still a little confused
Instinctively I tried the stiff arm solution, seemed to get worse, I did think this would be similar to the steering damper idea.(At least that's what wet through my mind at the time). Seeing this didn't help, while I kept the throttle as constant as I could, I relaxed my arms, the bike did seem to be settling, the frequency was decreasing. Until the rear regained grip - I am guessing then a high side, just completely threw me, I wasn't expecting the highside.

From the posts in the thread I am a little confused about how to attack this type of situation.
I my mind loosening my arms seemed to be working any one else agree/disagree?

NO I am not overthinking this or overanalysing it either, just interested in others thought more experienced than me

[Katman]

Since reading it, i am still a little confused

No kidding.

[eldog]

No kidding?

Enlighten a simple soul, who seeks wisdom from others.

Are you referring to the thread or to my post or both - now I am confused

[haydes55]

So you had a tank slapper, at the same time your rear wheel was sliding? Tbh that sounds like a fucking difficult situation to correct. In a tank slapper it's hard to moderate the throttle. But ideally you would want relaxed arms, lean back (although that might depend on what riding position your bike is) and slightly accelerate. Lifting your elbows allows you better control of the throttle, as does holding the throttle like a screw driver. But again, it's sometimes impossible to adjust your grip in a slapper.

High siding is caused by your bike pointing a direction that is different to your current direction of momentum (I.e. Where you would be going if it wasn't for the slide), when the bike regains grip. Ideally you will maintain the broken traction until your bike is pointing in your direction of travel. This is very difficult. Don't shut off the throttle (unless your rear end stepped out whilst breaking with no throttle, don't suddenly apply throttle). Get your weight into the inside of the bike, relax the steering (front wheel should stay pointing in the right direction if you relax your arms). You could take your outside foot off the footpeg to drop your body further into the inside of the bike (but that's debatable, just what I learnt from speedway when a highside was brewing, I've only had 2 or 3 rear wheel slides and haven't been thrown off yet, and all those times I lifted my outside leg off the peg and squatted onto my inside leg).

You can see the cure for both is fairly similar, keep the load as even as smooth as possible and relax the arms.

The best cure is prevention, maybe look at what lines you take into and through corners, how you apply throttle through the corner and how you read the road and identify hazards.

Again, just to reiterate, this is just what I have learnt from speedway and road riding. This info is what I do in these situations, I have thought about it and analyzed it in my head, so when it occurs I react instantly. I am not in anyway a riding instructor or 65 year old guru.

[DamianW]

In addition to keeping the throttle open and moving your weight forward I'm told that lifting your bum off the seat also helps.

[eldog]

In addition to keeping the throttle open and moving your weight forward I'm told that lifting your bum off the seat also helps.

I know I was already in this position - of the seat leaning in with head and body, keeping the bike vertical as I went into the corner speed 70 (corner is an easy 90k most of the time)when the rear slid out, this most likely reduced the amount of weight on the rear, when I hit the tar bleed (couldn't see it in the wet and dark, but he weight forward may have helped stop the front from sliding). The tankslapper happened after I wrenched the bars back. As the tanskslapper was reducing- almost ended- suddenly the rear got traction - highside - getting a big boost, then looking down and seeing the bike about 1+ metre beneath me, just going about is business driving along, not a care in the world. The air time I got was great. Oh yeah! I thought, this is what those motocross riders do - now where are the handlebars

[BlackSheepLogic]

I think this would shift weight onto the front which is not what you want to do in this situation.

In addition to keeping the throttle open and moving your weight forward I'm told that lifting your bum off the seat also helps.

[DamianW]

I think this would shift weight onto the front which is not what you want to do in this situation.

I've read in a few places that moving your weight forward and onto the pegs will lower the bikes cog and reduce whip effects of the rear regaining traction. I saw this in last seasons BSB series when I think it was Chris Walker was coming around the final bend at Brands and for all money was high sided. He got his arse off the seat and body forward and saved himself. Under slo-mo replay it was extraordinary to see just how quick his reflexes were working. The feel those guys have for their bikes is beyond mere mortal me.

[James Deuce]

The only way to fix a tank slapper is to get the front wheel OFF the ground. Most people who say they saved a tank slapper, including top level racers, are bullshitting. It was luck.

[eldog]

I had the combo, rear slide, tank slapper, highside.
Its something I have learnt from. Just didn't expect them one straight after the other. It as like OMG what next. Ah yes, I am lying on a 100k road and a car is coming fast. Get up and off the road you idiot.

I was lucky I could ride the bike home. Even though I couldn't move my right arm at all, just twist the throttle and apply the brake was all that side could do. Used left arm to lift the right hand into place. Ten feet tall and bullet proof I was. Till I got home....

Worse was telling those who love me that I had had an accident. That was way worse.


Reducing the weight on the front seems like a good idea to minimise the bounce.