Headshake, Tankslappers?

[MSTRS:Me]

I had a sealed, nonserviceable damper on the 1100 that shit itself. Straight away, I noticed the headshakes under heavy acceleration out of corners. Replaced the damper - voila, no more headshake. Guess it all depends on how hard you wanna push your bike as to whether you need a damper?

[bugjuice]

I had a sealed, nonserviceable damper on the 1100 that shit itself. Straight away, I noticed the headshakes under heavy acceleration out of corners. Replaced the damper - voila, no more headshake. Guess it all depends on how hard you wanna push your bike as to whether you need a damper?

and the kind of bike you have.. But yeah. If you seldom ride hard, then you'll probably never ever need one. But if you have a sports bike that's a bit twitchy and accelerates well (with sticky tyres), then you'd be better off with one. Lets face it, you have a sports bike, you wanna spank it now and again

If I had a dollar every time I needed one, I'd have about 30 bucks at the moment.. but still, I'm saving..

[2_SL0]

So here is the question, I was busy saving my dollers to buy some leathers. (I already have a Dririder jacket and pants etc.) but should I buy a damper first. Plus being winter the Dririder gear is going to be warner and more waterproof. So wait for summer and then buy leathers etc.

[bugjuice]

So here is the question, I was busy saving my dollers to buy some leathers. (I already have a Dririder jacket and pants etc.) but should I buy a damper first. Plus being winter the Dririder gear is going to be warner and more waterproof. So wait for summer and then buy leathers etc.

well depends on how you intend to ride over the winter. And how you have been riding. If you haven't got one yet, then do you need one right away? By buying leathers, this will increase your mentality on the track and road, so you will be riding that bit harder, which may give you more slaps.. Or just back off a smidge and play it safe until you get the damper. Coming into winter (despite what I just said), leathers could be a bit cold, and in the wet, a damper might come in handy..
You'll eventually have both, so I guess just buy one or the other and save again..

[Ixion]

..

As for what causes it, playing with the suspension set up and tyres can help, but the main reason for the cause is too much acceleration and the front wheel starts to skip the road surface. Then it catches the road at an angle and rebounds back, but that's too much, so it bounds the other way and so forth, then you're a slapperin a way. A damper helps to slow down the side-to-side motion and regain control quicker.

Dunno- I'm sure that causes them, but they can also (on older bikes anyway) just "grow". The bars start shaking to and fro , and the shake gets worse and worse until it's slapping side to side. Braking or deceleration makes it worse. Acceleration is supposed to be the cure, but it takes cast iron balls to turn up the wick when the front ends gone insane ! We didn't use to have hydraulic dampers, just the friction ones , winding them up tight helped. My old A10 was a beast for it until I rebuilt the steering damper, it had had a sidecar on it though, don't know if that had some effect.

I always blamed frame flexing , but that was probably just me parroting something I'd heard (from someone else who didn't know either )

I imagine the underlying physics is probably the same though.

[TwoSeven]

I have always had a weird view on steering dampers - I dont use them, so probably talking bollox

To calibrate a damper you need to know how a head shake (it’s different from a tank slapper) occurs. Following is my theory.

Basically when the load of the bike is transferred from the rear of the bike (acceleration or in extreme conditions constant speed) to the front of the bike (de-acceleration), extra weight will be put on the front tire, especially if the front shock is not set up properly to slow this transfer down. What happens next is that the tire will attempt to deform in order to cope with the load - the lower the tire pressure the more it will deform and squirm about. When this happens your rake/trail is changing which causes the tire to try to turn around (and face the other way) or at least to start doing that – that causes the bars to oscillate. There are ways to induce this to make it happen, but I wouldn’t recommend it.

Anyhow, the role of the steering damper is to cope with this oscillation and slow or retard it. On the track there are two main causes – first one is under-inflated or cold tires (remember basic rule – 1psi expansion per 5deg in temp – depending on brand of tire – you’d know your rate based on your log book records). So many racers will drop a couple of PSI at the start of the race knowing that their tires will expand after a couple of laps when they get warm. Problem is, it increases the amount of deforming that tire will do when you promptly accelerate blindingly hard then wail on the front brake. Even if you do have the correct tire pressure, its possible to still hit the front brake hard enough and feel the front end moving around - that’s the second cause - just as well you hopefully haven’t got the biked leaned over or it will bin you rather quickly.

The trade off with a damper is that while it reduces front end head shake, it also reduces the amount of steering input and feedback you get. The other trade off that a bike that is not tracking properly in the front end, will not be able to go as fast around a corner as one that’s working nicely - you wont know this, because its masked with the damper.

The reason why I said I like freedom of movement on the road is because the road has way more bumps and potholes – if the front end cant move about and be deflected to some degree the force will go thru to the rider or somewhere else – sooner or later something will break - and sometimes will cause the next problem.

Out of interest, as far as I know a tank slapper is caused by the front end not being able to move about. Too hard a rider grasp on the bars or over tightened steering head, solid steering damper yada yada. What happens is the oscillation travels down to the back wheel (because there is nothing to absorb it), then comes back up the bike – sine waves are additive in this case so the amplitude doubles each time it goes up and down the bike. Eventually it ‘will’ force the bars to move but with sufficient force for you not to be able to do anything about it. It [the cause and effect] also happens blindingly fast although often you will notice that the oscillations are quite slow – sometimes you just get a nice little wallow or weave.

Anyway, once you know the point at where the headshake occurs, you need to increase the steering damper to limit that – but not too much that it causes high speed weave or a tank slapper.

Also, don’t confuse this with a light front end which is just the rider wiggling the bars or some minor muck causing interference under acceleration – that will go as soon as the front loads up again and damps it all out. Note, you’ll also get this kind of wiggle from too high a tire pressure and/or too steep a steering angle (high speed wobbles) which again if amplified can cause a tank slapper.

I’ve never really looked at the math for it (and I don’t want to ) – but that’s my theory of head shakes vs. tank slappers. It may be all woffle as far as I know.

[MSTRS:Me]

It may be all woffle as far as I know.

Damn good read tho.
I've been led to believe that a steering damper shouldn't be able to be 'felt' in restricting movement - it's job is to slow the violent back/forward movement of the steering. Restricted ease of movement (by hand) is only necessary at track racing speeds.

[Toast]

Don't tank slappers also occur when the back wheel steps out and the front reacts to keep itself going in the same direction as the rear? I think I read that somewhere.

It all got put in to more understandable terms one night when I was coming back from Uni on the old CBRtwofiddy. I flicked it in to a roundabout (by the manly shops on the Whangaparoa penninsula) in the pouring rain at about 50 or 60km/h (feeling right brave that night I was), got the gas on, felt the back step out, and then nearly had my wrists broken by a massive $%^&'n slap from the bars...bike stayed upright, I probably looked like a legend (though no one was watching at 9pm), nearly dirtied my 'L' plates. Point of the story: seems like solid theory to me.

[Two Smoker]

Don't tank slappers also occur when the back wheel steps out and the front reacts to keep itself going in the same direction as the rear? I think I read that somewhere.

It all got put in to more understandable terms one night when I was coming back from Uni on the old CBRtwofiddy. I flicked it in to a roundabout (by the manly shops on the Whangaparoa penninsula) in the pouring rain at about 50 or 60km/h (feeling right brave that night I was), got the gas on, felt the back step out, and then nearly had my wrists broken by a massive $%^&'n slap from the bars...bike stayed upright, I probably looked like a legend (though no one was watching at 9pm), nearly dirtied my 'L' plates. Point of the story: seems like solid theory to me.

Ive never had a tank slapper from sliding it (whether it was a similar account of yours, or on the track at speed...) Tank slappers happen when the front wheel lands slightly a-scew (wheelie or front skips because of speed) and then progresses its servareness...

[Matt Bleck]

Me Gixxer has a tendency to head shake with the right ingrediants: hard acceleration, the front wheel getting lite, or hitting one of the many potholes on our roads. And each time I've kept the gas on and she's come right.

[Toast]

Ive never had a tank slapper from sliding it (whether it was a similar account of yours, or on the track at speed...) Tank slappers happen when the front wheel lands slightly a-scew (wheelie or front skips because of speed) and then progresses its servareness...

I'm thinking maybe it was a similar case to the phenomenon of just gassing it hard and lightening up the front...and maybe I rolled off slightly and that made it all worse...I dunno aye, was a long time ago now...I tend to take it easy in the wet, and am not keen to get the new bike wild at the rear yet.

[sedge]

I've got a theory too What causes tankslappers

I reckon it really has to do with a combination of gyroscopic force and deformation. (patrially ripping off the previous deformation theory, I have thought about this before though)

We all know that turning a spinning wheel produces force at a 90 degree angle to the spin right ? That's what keeps us upright on a bike, the force needed to overcome the gyroscopic force is greater than the force generated by the spin (of course put enough force in and you'll fall over)

This is also what allows us to counter steer, turning the wheel away from the corner will apply force to the bike to tip it into the corner in the opposite direction.

I get a wiggle under hard acceleration, this is normal. The real tank-slappers occur when you alter the geometry of the bike, EG you come over a crest, wheel goes light, then you land it, wheel slightly off line, the tyre compresses and deforms. Force is still applied by the bike moving forward, but the wheel is off centre, this causes same effect as countersteering with the handle bars.
Each time the tyre deforms it presses in to the road, then rebounds and lifts up, damping load is then over applied to the opposite side due to the lightness of the front end, the counter steering effect is amplified in the opposite direction. Repeat.

Dampers work because they are perfect dampers, people aren't, they have a inconstant damping rate, IE people react to each movement and under/over amplify. Tankslapper.

What do ya reckon ?

Sedge

[sugilite:Me]

I've been buying steering dampeners for my bikes since the days of the dreaded 16 inch fronts.

I've had my fair share of tank slappers, even snapped a few steering stops along the way. I've never come off from one, but I've sure scared myself!
The last one was last year at manfield when my dampener broke of the frame (rivets broke) it started at the seal change just out of higgens and I did not gain control until 2 upwards gear changes and the 200 meter board for the sweeper, waaaaay to much time to think about it!

I use 2 techniques to get out of them and it depends on speed and circumstance as to which one I use.

Option one: slow speed - if you are on a reasonably powerful bike and you are in the lower gears, pop the front up and wheelie out of it. The last time I used this was on the 1st model TL i was test riding, it was before the recall done on that model to have steering dampeners fitted!
I was up mt vic in wellie, went to pass a bus load of jap tourists and it bloody tank slapped the length of the bus (I think they were quite excited with their birds eye view of it!), pulled said wheelie and re grounded the front wheel then pumped the brakes up again (more on this later)

Option 2 - high speed. Simultaneously lie on tank, clamp arms over knees (I'm tall, not sure how this works for shorter riders) to lower the CG forces and hold on tightish (hold on to loosely and you will snap your wrists like twigs) and accelerate as hard as you can, you may even need to change up to keep the acceleration going, never, never give up until it comes right (I was seriously looking at jumping ship for my last manfield one as I was not sure I was going to get it under control before the sweeper!), then pump the brakes.

What is this pump the brakes stuff?
Well, when you have a bad tank slapper, the front wheel twists against the brake calipers and opens up the brake pads within it, so after your 1st near heart attack moment, you get rewarded with a 2nd as you go for the brakes at the next corner! (yep, happened to me, and people thought the stain on the road was left by a sheep truck!)
For my worst slappers, I've had to pump the lever right to the bar 3 to 4 times to get them back!

My overall advice is, if you have a sports bike without one, and you like to ride fast....GET A DAMPENER NOW!
All it can take is a higher profile replacement tyre and that can be enough to alter your rear ride height changing your placid steering bike into a slapper!

[Teflon]

Use to get shit loads coming out of corners from the front wheel landing crossed up, but i ride to slow to get them now.

[Kornholio]

My 01 GSXR has one standard and I have had a few little wobbles but nothing like my 89 GSXR....that definitley needed one, had passed a car on a bridge once and when the front wheel hit the lip at the end of the bridge under full power the bars started shaking, I could hear the front wheel screeching on the road(I thought my arms were going to break) but I buttoned off a bit and all was calm until I came into the next corner and needed a bit of brake and there was nothing there.... Apparently the discs were warping and had rammed the pistons back into the caliper... a few pumps and all was good

This happened on several occasions but decelerating seemed to make it all better