|Originally posted by suebrown:
... In other words, is it ever the case that ski choice could affect the amount of chattering? ...
After I had a chattering problem with my 9.16's last season, this question has been on my mind, so I did a test one night when the mountain was a sheet of ice.
I brought 5 pr of skis out to the mountain. Some of these were oldies, but all are considered "shaped" and all have served me well in icy conditions. Here are their specs (all actual measurements):
Head xp100 - 123/68/107 mm x 184 cm ( 14 m sidecut radius) - medium stiff - bevel: 1 deg base - 2 deg side
Atomic 9.16 - 105/62/94 mm x 170 cm ( 15 m sidecut radius) - medium flex - bevel: 1 & 3
Volkl p40 - 101/64/87 mm x 188 cm ( 23 m sidecut radius) - stiff - bevel: 1 & 1
Elan SCX monoblock - 115/60/104 mm x 193 ( 14 m sidecut radius) - extraordinarily stiff - bevel: 1 & 3
K2 Enemy - 110/74/97 mm x 173 cm ( 19 m sidecut radius) - medium-soft flex - bevel: 1 & 1
The stiffness is my own estimate. The bevels are not all factory specs.
I tested all of the skis on the same patch of ice at Ski Liberty (PA) - a short black trail, maybe 25 feet wide. There had been light skier traffic all day. It had rained and then frozen into a sheet of some of the smoothest, highly reflective ice I have seen in a while. I tested all the skis within about an hour, and because of the conditions, there was no one on this trail but me all night, so the surface did not change between runs.
All skis were hand tuned (by me). I'm not a big believer in de-tuning the tips and tails, so all were sharp from front to back. All could be made to hold at a dead stop on this pitch. The Enemies required a bit more angulation to keep them from sliding out, but also held.
I then did slow controlled sideslips (no forward motion whatsoever). All of them did so smoothly with the exception of the 9.16's, which caught and released (ie, chattered) no matter what I did in terms of stiffness of my legs, stance width, etc. If I decreased my edge angle further and did a fast sideslip, then the chattering on the 9.16 decreased more, but always seemed to be on the verge of doing it.
I then did short radius turns on all the skis. For some of them, their sidecut radius and/or stiffness prevented pure carves, but they all could be made to ski without chatter, including the 9.16's. The 9.16's were short and soft enought so that I actually could carve most of each turn with them, and once moving forward at a decent velocity and locked in on an edge, the chattering disappeared. If I skarved more of the turn with the 9.16's, the chattering reappeared.
My take on this test is that:
1) Skis can chatter even when there is minimal technique involved (ie, a zero forward velocity pure sideslip).
2) Yes, equipment does make a (big) difference in chattering, particularly when there is any sideways component to your velocity.
3) In pure carves chattering can be eliminated, even on chattering prone equipment, but it often is hard to execute pure carves, so often you are dealing with situation #2, above.
4) The 1 (base) - 3 (edge) bevel on the Atomics and Elans was unique within this group of skis. Their edges clearly felt sharper than all the other skis. When doing zero forward velocity sideslips on the 9.16's, the grabbing was definitely in the tip and tail, not underfoot. My feeling is that when the tips and tails grabbed, they *really* grabbed (as compared to the other skis). As the waist continued to move downhill but the tips and tails held, the decambering got too large that the tip and tail couldn't hold anymore compared to the underfoot area, then the tip and tail would release, the decamber would decrease, and this would start the catch and release cycle again.
Even though the much stiffer SCX's had the same bevel and similar sidecut radius to the 9.16's, they did not chatter at all in the pure sideslip test - the tips and tails released and caught at the same time as the underfoot area. The good side of the stiffness of the SCX's is their lack of chatter. The bad side is that because of the stiffness, you can't carve as tight a turn on them as you may think based only on their sidecut radius.
Even the relatively fat Enemies were surprisingly maneagable on this ice, but because of their radius and torsional softness were limited to skidded turns.
My favorite skis for this pitch was actually the 9.16's in spite of their propensity to chatter. The were the only ones I could fully carve on, and felt the most secure. If the pitch was just a bit wider or I wanted to risk a more straight line path, then the xp-100's would have been my choice as I could have carved on them without any worry about chatter.
If I was going to handle ice using purely skidded old-school technique, the p40's would be my favorite. The SCX's would be a close second (again, only for pure skidding technique), but are a bit too sensitive to little irregularities in the ice compared to the p40's.
I know this was a very long answer to your simple question of whether or not equipment makes a difference, but I hadn't posted the results of this test before and thought that people might be interested in some of the details.
Tom / PM
PS (in edit) - I just saw Josseph's post after I finished composing this one. It looks like we agree almost totally. That's awfully reassuring.
PS#2 - Although my tests above didn't speak directly to this, I agree with the other contributors who said that chattering can be minimized (and sometimes eliminated) by appropriate technique even when skidding is involved. Conversely, however, there also are situations (ie, my pure sideslip test) where technique hardly is a factor and you just can't stop chatter on some equipment.[ March 02, 2004, 11:52 AM: Message edited by: PhysicsMan ]