what causes chatter in skis?

A snowHead

Occasionally when going in a straight line on my skis, I get some mild chatter on the front, i.e. the ski moves a tiny bit from side to side.
I can't work out whether this is me not pushing down on my toes enough (my stance is usually okay and I can feel pressure on my shins in the boot so my weight is over the skis) or whether it is something in the skis...or just slight variations in the snow pattern on the ground.
Any ideas?
I've heard that Head Monsters (iM 72s) don't go well in a straight line but can't think why. I have had this effect with other skis but never ever have a problem when they're on their edge so must be me somehow...
Any thoughts on what to check or stop this from happening?

A snowHead

I'd put the skis on a very slight edge even when supposedly straight-lining so you get those tips to engage.

Well, the person's real but it's just a made up name, see?

Don't you start turning then?
Also, why do you want to engage the tips? To prevent from catching an edge?

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Well you've already checked the first possible cause - are you 'driving your boots'? If you're sure that you stance is centred & that you're ankles are flexed then your binding position could be a tad too far back for your individual balance.

Lack of ski stiffness for your weight/too fast for the ski stiffness usually causes chatter, ie vertical vibration of the tips.

If the sksi are just moving a bit from side to side it's probably to do with the ski shape. Many skis with wide tips'n'tails & tightish sidecut don't straight line too well. The manufacturer's often put a tad of concavity in the tips'n'tails to help straight line tracking (like my old Atomic B5's). Try keeping them ever so slightly on edge rather than flat. It can be a bit disconcerting at first but you'll get use to it.

Boot set-up/alignment could also be an issue, ie ski bases aren't truly flat when you think they are. I had this problem until my boots were planed but it meant I was always on edge so I didn't get any movement on my B5's when schussing. Once my boots were sorted the skis became twitchy when schussing rolling eyes

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GordonFreeman,

You are letting the edge do the work rather than let the tips flap around. The edge set is so slight you'd not notice a devaition off line. Only racers need to glide anyway

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spyderjon,

GordonFreeman, This chattering phenomenon never seemed to happen with the old straight ski's so me thinks its something to do with trying to ski in a straight line on shaped ski's designed for turning. I don't know whether this is the correct solution, but I tend to tilt both ski's very slightly onto their inside edges when travelling in a straight line at speed, and ensure my shins are firmly in the front of my boots with my weight centred over the ski's.... result.... no chattering. Alternatively forget straight lines and do what the ski's want to do.... big carved turns at high speed.... great fun Very Happy

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GordonFreeman,

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I have a pair of the old style B2s (fairly soft) and when going flat out with the bases level they really do start to chatter with sideways movement of about an inch each way. As said above - the best remedy I found (even in a full crouch) is to engage the edges just a touch and do very shallow turns. Stable as anything then Cool

spyderjon, It's difficult not to hit rocks when you ski Salzburgerland in a season such as we're having Very Happy

Thanks for repairing the Atomics... I'll pick them up later in the week !!!

You know it makes sense.

T Bar,

Obviously, not many peeps got that.... Laughing

Otherwise you'll just go on seeing the one name:

JT, I got it, but found it soo distatefully non-PC that instead of commenting I reported it to the forum police Laughing

A snowHead

A snowHead

For what it's worth I find my IM72s rock stable at high speed. But I've only used them in excellent snow conditions. I always think of "Chattering" as a rapid under-damped vibration of the ski tips at high speed, which I’ve never suffered with Head Monsters. From your description it sounds more like the skis are wandering and not tracking perfectly straight. I find all shaped skis do this to some extent and much prefer being on edge to running dead flat. The relatively small base angle (0.5 deg) might be a factor, since it makes the edge bite with very little roll angle. You could perhaps try increasing it a little.

Well, the person's real but it's just a made up name, see?

GordonFreeman, I don't think that's chatter myself. IMHO, Chatter is when your tips and tails are vibrating up and off the snow because you're going so fast they can't properly absorb all the energy. More of an issue with old straight skis for some reason...)

What I think you're describing is indeed due to the skis being almost flat and having so much side cut that the tips and tails are "catching" ever so slightly. Stick them on a very slight edge and this should stop.

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I thought that for max speed (not something I often want, but on the flat I do) the ski should be on a slight edge, not flat. The slight turn that results is more than compensated for by the increase in speed (so the theory goes). It seems to work for me; is it in fact balls?

Anyway, snowHeads is much more fun if you do.

richmond, Don't know about "balls" but my understanding is that a ski will glide best when perfectly flat and not on an edge - more of an issue in a downhill or a flying K than a problem for most of us. This may illustrate why flying K skis aren't shaped ( wink

).

Funnily enough, someone was skiing around in Champoluc at the weekend on a pair of 238s...I assume the local world speed record or his little brother. No sidecut to those puppies.

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I had proper chatter once on some hired straightish skis in Canada. It was our 4th day skiing and myself and my mate decided to go flat out down from a top as it had a massive run out at the bottom. In a crouch it felt like I was skiing over loose Lego bricks with the vibration hehehe

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I agree with David Murdoch and uktrailmonster, chatter is a vibration in a vertical direction of the tips and tails of the skis, at high frequency, causing it to vibrate. It's something to do with the resonant frequency of the ski.

I think that the characteristic that Gordon Freeman is describing is wandering of the ski when not on an edge, ie yaw movements. As mentioned before you can either choose an edge and stay on it slightly, or just relax your leg a bit and let the ski wander.

After all it is free

I agree with David Murdoch, chatter is a high speed vibration damping issue. Modern high end skis have pretty much eliminated chatter, at least at real world speeds. Sometimes get it on knackered hire skis or from pushing lower end skis to their limit.

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yaw is exacty the word I was looking for.
I'll just shove it on edge next time.
The problem I have with yaw, going at speed, and my 0.5 base edge is why I don't like it much ! Shocked

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I did a great one recently - flat out in a straight line down an easy blue, looking around in a nonchalant manner at the surrounding mountains... when an outward yaw in the left ski coincided with a bump of soft snow. The aforementioned ski shot off my foot as I did a rather more rapid impresion of a teenage mutent ninja turtle and span on my shell. Always pay attention folk rolling eyes

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Isnt chatter caused from going too fast... as in you dont have the strength to keep the skiis straight at such a velocity? I know when i hit 80km/h the skis begin to chatter a tad bit for me... on carving skiis, i dont ever remember the skiis chattering on my downhill ones but that was yeeeeeaaars ago...

Timmaah, no, thats the 'yawing' movements described above. I find it a little interesting that Kramer doesn't speak of damping the yawing motion using the femur rotation muscles. Sometimes it is referred to as 'squirrely' or 'unstable'.

'chatter', as DM and others describe above, is the term I use to describe rapid engagement and disengagement of the ski edge from the ice when it doesn't have enough edging force applied by the skier (or torsional stiffness to transmit that force from binding to edge) to hold against the required lateral forces.

The required lateral forces are dependent on skier speed, weight, and the requested turn radius as specified by how much the ski is tipped and how much the ski is redirected away (in the yaw sense) from the direction of skier motion (quite often the fall line). Perhaps it is the latter point that causes confusion?

One could quite easily have 'chatter' on old-style straight skis, particularly when the skis are significantly redirected by the skier from the direction of motion such as in 'windshield wiper turns' (which aren't really turns at all) or hockey stops.

You know it makes sense.

comprex, I must admit I was thinking of the chatter one got on older style skis when travelling (probably on hard pack/ice) v. quickly.

Your description sounds more like what happens when you "brutalise" the snow if I may use an Americanism?

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A snowHead

David Murdoch, Kramer, it is certainly possible for the ski to lose contact with the surface in sections along the length when it is run flat, but I see that as merely a subset of the entire set of chattering conditions. In all sets of chattering conditions, there is a failure to distribute applied pressure from the underbinding area to the surface. In the case you both cite, the pressure is merely body weight, with no edging pressure component, and I would consider that a bad ski for the conditions indeed.

'Brutalising the snow', again one subset, unless we consider the skier ultimately responsible for everything that happens with the ski. It might also happen with terrain undulations when edged, or surface changes when edged (say going from a snowy bump to the scraped ice beneath or to the side of it) to name more instances that are harder to blame directly on the skier.

Kramer, you pointed out the resonance problems along the length, where a first shock excites an oscillation at a resonance mode of the ski. Rightly so, but I see no reason to limit that to longitudinal modes. The ski can oscillate across its width also, and also within only a part of its structure. It is perhaps difficult to see this at first as we are so used to seeing extremely well-tuned systems like bells and guitar strings, rather than broad, shaped, diving boards that can also twist. Anyhow, if those oscillations cause contact failure with the snow/ice, I call that "chatter".

Yawing: well, Kramer, you're fortunate in that you have skis well-suited to your style and speed, and possibly a quite clean turn release also. It is nice to be able to go where one wishes to without argument from the gear, yet I do not speak only of conscious damping, mind. The unconscious damping could quite well be a part of 'dynamic balance and good posture over the skis', so that one succeeds in ones conscious wishes? I find this topic highly relevant both to the redirection at the top of the turn FastMan mentions in some of the carving threads (an instance of conscious-mind yaw control), and to the recent boottop fracture discussions elsewhere (an instance of unconscious-mind yaw control failure, perhaps).

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what causes chatter in skis?

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