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Do conventional (i.e., non "integrated") bindings interfere with ski f

post #1 of 20
Thread Starter 
The conventional claim is that clicking into a normal (i.e., non-"integrated") binding will interfere substantially with the flex of the ski underfoot. I feel that this is extremely unlikely, and think that the beneficial effects of these systems arise from other effects. For example, in an earlier thread, AarHead pointed out that simply removing the normal stiff binding mounting plate from a ski will increase the flex of the ski in the underfoot region.

To see if the conventional claim has even the remotest possibility of having some validity, I calculated the increase in stiffness of the underbinding area of the ski due to a stiff spring (i.e., the forward pressure spring of the binding) placed on infinitely rigid posts (i.e., the conventional binding) above the ski. Fig. 1 shows the geometry I assumed:

[img]http://groups.msn.com/_Secure/0WgCMOOYd!6CgVU0yXpBC9BDWWyrxmqz3V*F4ehDr66tWljtxR mvizMZ8cVT!EN*PS6QERVzZqn0ViosJ81Kf7lelK1b7kiR*Wrg dewrYR!ZsCTg*SA4!YwBJZB6rQ2*cSalz8KMXRx8/cent erofskiwithbindingabove01.jpg?dc=46754361221339461 18[/img]

This is a simple modification of the analysis geometry used in Lind and Sanders, “The Physics of Skiing” (Fig. 2):



A simple force & moment analysis shows that the extra bending stiffness introduced by the external spring is:

Bextra = k * h^2 * L

Where k is the spring constant, h is the height of the boot-sole above the top-bottom center of the ski, and L is the length of the boot sole.

Even in the case of the stiffest binding forward pressure spring measured by Arnold in the earlier thread, 34000 Newton-m^2, and assuming an “h” of 1.5 inches, and a length of 1 foot, I calculate that Bextra is approximately 15 Newton-m^2. Actually, this number is an upper bound on the actual value as any flex in the binding or its attachment to the ski will reduce this value.

Fig. 3 shows a plot of the local bending stiffness, B, for several skis as a function of fore-aft position along the ski. This figure was also taken from Lind and Sanders, “The Physics of Skiing”.



Note that even the softest skis have stiffness in excess of 300 N-m^2, whereas the extra contribution of the binding is at most 15 N-m^2, i.e., a negligible 5% of the ski’s intrinsic underfoot stiffness.

Many other effects can contribute to the change in performance of skis when going from conventional to integrated binding systems. As mentioned above, simply removing or modifying a conventional in-ski attachment plate will reduce the stiffness of this section of the ski, no matter what is attached to it.

Other likely effects of “integrated” bindings include damping of the ski, isolation of the boot from various high frequency motions of the ski including the usual up-down motion, but also including pitching, etc. These effects can easily lead to a different feel for skis with integrated bindings.

As a final, somewhat exaggerated example, look at Fig. 4d. This cartoon of a rail-like mounting system exaggerates what might happen if load is applied at widely separated fore-aft points on a soft ski on soft snow – the mid section could even go into reverse camber.

[img]http://groups.msn.com/_Secure/0VgDPAnIcnB4xs6zRQk1uIcoWhKU3Ra51rjTMAqwc8yJLV!1w8 xdRTUsBK3X1W03Hvh*RujnW6vn!5memJmeryQTiR3yj4!iHKl4 4X2B0iTKjUWhCnBC*miH*sw2EyJ0p/skiswithvarious bindings01.jpg?dc=4675436133868083102[/img]

If the mounting points for the rail are far enough fore and aft on the ski, even a slight fore-aft weight change by the skier will dramatically change the pressure distribution of the ski on the snow, making the ski seem very sensitive. On the other hand, if the rails themselves flex, much of this effect will be removed, but vibration isolation will be increased.

In conclusion, I feel that integrated binding systems give ski designers more options while simultaneously reducing the uncertainties associated with after-manufacture mounting. However, I also feel that the oft heard claim about boots in a conventional binding interfering with the ski flex is pretty much nonsense (except in unusual cases – ie, extremely soft skis, long boots, very high mounting of conventional bindings, etc.).

Comments?

Tom / PM

PS (in edit) - Blankety-blank long URL's seem to confound Epic's text editor even though I am using an "img src" command instead of the usual UBB image command (a work-around suggested by Mark XS, and which previously worked). Anybody know how to fix this? If not, just cut and past the URL's into your browser manually. Sorry.

[ August 29, 2003, 10:15 AM: Message edited by: PhysicsMan ]
post #2 of 20
Tom,

try this site:

http://tinyurl.com

the UBB image tag command works with the URLs that site generates for you

[ August 29, 2003, 10:10 AM: Message edited by: Ugli Pupferknick ]
post #3 of 20
Thread Starter 
Thanks Ugli. I have always hesitated using Tiny URL and the other similar service, because I was never sure how long they would keep the new URL's active. In this case, I'll deal with archival issues when they arise.

Thanks again,

Tom / PM
post #4 of 20
Tom:

Thank you for all of the technical analysis. While I follow the gist of it I certainly do not follow the detailed physics of the analysis. I completely agree with your conclusion about integrated ski-binding systems in that the one general benefit all ski binding systems have over non-integrated systems is that the designers have a complete understanding of the flex characteristics of the binding that will be on the ski (I may be over generalizing here). While I have alot of thoughts about expansion on that theme I'd like to throw out a few questions instead. I don't intend them as counterpoints but more as food for further discussion / analysis. They are as follows:

1) How can the average dumb shopguy (note: I'm one of them) convey the above concept to the average customer quickly and easily enough to keep their attention and still promote it as a significant benefit?

2) If a rigid structure (typical of most heelpieces and some toepieces) is bolted to a ski using four hard mounting points about four inches apart what effect would that structure have on the flexibility of the ski in the area to which it is bolted to the ski?

3) Measured on a bench does a non-integrated ski with a typical step-in heelpiece have a measurable difference in flexibility when compared to the identical ski with a turntable heelpiece?

4) I know Dynastar and Rossignol use keyhole-slot style soft mounting points on the aft (and some fore) mounting screws in the plates that are part of their integrated binding systems. Do Atomic, Head, K2/Nordica/Marker, etc use soft or hard mounting point on all of the screws that are part of their systems?

I've always thought the argument about bootsole rigidity affecting the flexibility of a ski to be bogus due to the spring in forward pressure adjustments of heelpieces. On the other hand I've always noticed a performance difference between step-in and turntable heelpieces. I noticed that difference to be exaggerated beyond the feel of a turntable in Dynastar's AutoDrive. I noticed a further exaggeration of that difference in Salomon's Pilot. In Marker's Motion system I didn't get a similar change in feel until the aluminum rail system found in the 6 Star and the P60 GC and SC Racings. I just wonder what causes the change in feel.

Thank you,
Aar
post #5 of 20
Scientific calculations and computer testing will never offset personal feel. Different bindings will create different results. A true free flexing design will allow a ski to flex through its natural arc better than the same one without free flex. We tested this with ESS years ago where we welded the heel/toe connecting band to the rear tracks and mounted them on some downhill skis. Another pair of skis with the same flex and same length were mounted with an unwelded binding. The skis were supported on the ends by 2 chairs. One of World Cup athletes weighing about 100kg stepped into the welded pair and the amount of flex was recorded. The unwelded pair were then stepped into and they flexed way more. The visual difference was huge.
post #6 of 20
Thread Starter 
BetaRacer - I really like what you did because I agree totally with you that the best way to answer any question is by an experiment, not by a calculation.

In fact, a couple of years ago, I did a very similar experiment to the one you did, and first reported it in post dated October 09, 2001 12:42 AM in a thread on powdermag.com: Fat skis for a light guy

To summarize my experiments:

a) When the test ski was supported by points one foot apart, upon insertion of a boot in the binding, I saw a 25% change in flex when one ski was loaded with 150 lbs;

b) When the ski was supported by points one foot apart, I saw unmeasurably small changes in flex upon insertion of the boot when one ski was loaded with under 100 lbs;

c) When the ski was supported by points three feet apart, I saw a 5% change in flex upon insertion of the boot when one ski was loaded with 150 lbs;

d) When the ski was supported at its ends (ie, approx 6 feet apart), I couldn't observe any change in flex upon insertion of the boot when one ski was loaded with 150 lbs.

My experiments (a) and (b) support the calculation I reported in the first post in this thread. When the binding is working normally (ie, light to moderate loadings where there is still motion available in the forward pressure spring), the change in flex of the underfoot part of the ski is negligible. However, when the forward pressure spring is max'ed out, then the incompressible boot is being "pinched" by the binding and one does see a significant (25%) change in flex in the part of the ski directly under the binding.

My experiment (d) is most like yours - we both supported the test ski all the way out at its tip and tail. Unfortunately, our results differ dramatically: I saw no change in flex, whereas you saw a large change.

I don't know what is the cause of the difference between our results, but I will point out that even though I advocated a jury-rigged setup with two chairs and 5 gal cans of water in an earlier post in that PowderMag.com thread, I eventually was forced to go to a real lab setup (as I described) where variables were better controlled because small movements and deformations of the chairs made for objectionably large changes in the observed flex. In addition, I would be very suspicious of using a person to load the skis instead of a dead weight. The very first time I tried this experiment I also tried it with a person, and the jiggling and unequal L-R weighting were too much to give any precision to the measurement.

In addition, because of the vastly greater flex of skis as you go towards the tip and tail (see my Fig. 3 above for quantitative data on this), I would expect that one could make the center of a ski rock solid and barely perturb the overall flex.

Anyway, thank you for reporting your results. It would be great if we could combine forces and do a joint repeat experiment together.

Tom / PM

PS: Aar - You raised some very interesting points, but there's so many of them, let me respond to them later this weekend.

In edit:

PS#2 - When doing a search for one of my own posts, I just was reminded that I also posted these experimental results in Epic about a year after their original post: “Markers blow, Salomons suck, Looks rule...”

PS#3 - The reason I did the calculation after having done the experiment is that I have continued to hear people claim that the boot significantly stiffens skis. Since I couldn't find anyone that had done a similar experiment to confirm or refute my results, I wanted to double check my results with an order-of-magnitude calculation.

PS#4 - BetaRacer: If you did your measurements on a very short (ie, 150-160 cm), very soft ski, and a very long boot, this might partially explain the differences between our results. My measurements were of a 193, very stiff ski (old red SCX).

[ August 30, 2003, 02:51 AM: Message edited by: PhysicsMan ]
post #7 of 20
PM,
While I understand what you're doing, I don't think using point supports at the ends of the skis is an accurate reflection on the loading when on the piste.
In your fig 3, you showed the stiffness of the skis along their length. How would this graph compare with the actual reaction forces the ski is experiencing from the ground?
(OK, for the sake of this, we'll say the skier is centred and is either stationary, or travelling at a uniform velocity, i.e. no lateral or fore/aft forces)
What I mean is, as the skier is on his skis creating a downward force through his bindings, the snow is creating an upward force on the ski, so he doesn't sink. I would expect to see a graph of the forces acing on the ski to show the greatest forces are around the bindings, and then reduces as you get closer to the tips & tails.
(Does this make sense, or is my knowledge of beams letting me down again? [img]smile.gif[/img] )
So, now we have a case where very little reaction force is acting up at the tips & tails. Most of it is acting through the the area around the bindings. now, by having two bindings, you're creating forces around and inbetween the heel and toe which are counter-productive to efficient bending of the ski

And here comes my crazy idea...
The ultimate binding should therefore be one which only has one interface with the ski, creating a single load point. Create a single mounting point binding and you rule out the issues of inter-binding forces and flexing.

So, there's my concept (and reasoning) for what would, theoretically, be a perfect binding, now you go off and work out the forces involved in it and see if it is practically possible!

S
post #8 of 20
Thread Starter 
Quote:
Originally posted by Wear the fox hat:
While I understand what you're doing, I don't think using point supports at the ends of the skis is an accurate reflection on the loading when on the piste. ...
Thats correct. It doesn't. The only reason I did experiment (d) is that that's the way most people think about measuring flex, and in fact, there even is a ASTM (or is it DIN) standard to measure and report flex that way. The reason I reported it here was that support at the ends was the way BetaRacer did his experiment and I wanted to report comparable results.
---------

> ...In your fig 3, you showed the stiffness of the skis along their length. How would this graph
> compare with the actual reaction forces the ski is experiencing from the ground? ...
> ...I would expect to see a graph of the forces acing on the ski to show the greatest forces
> are around the bindings, and then reduces as you get closer to the tips & tails. (Does this
> make sense, or is my knowledge of beams letting me down again? [img]smile.gif[/img] )...

You are right on the mark, my man. Once again, from LInd & Sanders:



(I'm not going copy the text which explains which diagram goes along with which ski, because I don't think that would be covered by the "Fair Use of Technical Articles" copyright exclusion, but if you are interested, you really should pick up a copy of the book. Its THE BIBLE for this field.)

--------------

> ...The ultimate binding should therefore be one which only has one interface with the ski, creating
> a single load point. Create a single mounting point binding and you rule out the
> issues of inter-binding forces and flexing...

This is an excellent approach and is attempted by some binding companies who try to put their mounting holes as close as possible to each other.

Tom / PM
post #9 of 20
I could be wrong..and I'll admit it/stand corrected..if I am wrong..BUT I have GRAVE doubts whether an average ski could be bent/flexed..under similar weighted skiing conditions...that would lead to coil bind(complete compressing of the forward pressure spring)..forcing the heelpiece against the boot..and stopping/controlling the flex..
The only real fair test is to have the ski pressurized in the binding area by a ski boot..and then observe the travel of the forward pressure spring, and heelpiece.
Let's not forget that the ski..in the boot area ALONE..has to be effectively shortened by 1/2 an inch!..in order for the forward pressure spring to be compressed(backwards) into coil bind..thus jamming the heelpiece against the boot..and ending the on going flex.

I can get access to a few pairs of skiis destined for junk ..these can be sacrificed.

I'll have to figger out some way of pressurizing the skiis..with boots.Supporting the skiis at various points.And some way of observing..or marking/a tell tale or something.

I'll do this..I don't know when(NO time now)..and I'll of course post it.
post #10 of 20
Wow! I did not even read one word in this post. I just saw the diagrams and my brain started hurting. Ouch. Is it really this complicated. I go with the K.I.S.S. principle when I think about skiing. (Keep It Simple, Stupid) Hill + Snow + Lift - Gravity + Good Tune on Skis = Fun

Ty [img]graemlins/thumbsup.gif[/img]
post #11 of 20
Thread Starter 
Arnold said:

> ...I have GRAVE doubts whether an average ski could be bent/flexed..under similar
> weighted skiing conditions...that would lead to coil bind...

As I mentioned (on a different forum), I was also surprised that it only took 150 lbs of static wt on one ski to do this. I would have expected that it would take more like a 200 lb skier with all his wt on one ski, bouncing up and down to do this.

Perhaps it was just a bad mount job / boot length adjustment.

In any case, I can't wait to see your results. Any chance we can get together to do some of these tests? Where are you located? Feel free to send me a private msg.

Tom / PM

[ August 31, 2003, 11:39 PM: Message edited by: PhysicsMan ]
post #12 of 20
Thread Starter 
Quote:
Originally posted by Ty Webb:
...Ouch. Is it really this complicated...
It certainly isn't that complicated to ski on them, but if you want to understand and design skis, it is. Fortunately, I can assure you that I don't think of any of this nonsense when I'm actually skiing [img]smile.gif[/img] (...well, at least not too often ) .

Tom / PM

[ August 31, 2003, 11:38 PM: Message edited by: PhysicsMan ]
post #13 of 20
[quote]Originally posted by PhysicsMan:
----------
Quote:
Originally posted by Wear the fox hat:
> ...The ultimate binding should therefore be one which only has one interface with the ski, creating
> a single load point. Create a single mounting point binding and you rule out the
> issues of inter-binding forces and flexing...
----------
This is an excellent approach and is attempted by some binding companies who try to put their mounting holes as close as possible to each other.

Tom / PM
One of the things about current plate / integrated binding designs that I consider when trying to understand the effectiveness of these systems is the difference between hard mounting points and soft mounting points. I believe the first soft mounting points were engineered by Marker and/or Geze for mounting of toe pieces back in the late 70's or early 80's. The next evolution of the concept was with the forward mounting screws of Deflex plates. It is, however, the mounting system of the old EPBS plates and Hangl carve plates that strikes my curiosity in terms of this discussion. It is from those platforms that I believe many integrated ski/binding systems have evolved.

The EPBS plate is hard mounted in the middle of the plate at boot center mounting point of the ski but the fore and aft mounting points are keyhole slots that allow the ski some independence of flex from the binding. Many plates that followed - Rossi's race plates, Elan's early carving lifters, Dynastar's PowerFlex lifters, some Volkl lifters, etc either mimiced or evolved from this design in some way. Evidence of that influence still exists in systems like Dynastar's AutoDrive and Volkl's motion. Rossi's race lifter is still of a nearly identical design. Elan has moved the lifter under the Monoblock. Thus, my though is that some of these EPBS style plates may come close to achieveing Fox's ultimate binding as described above. I'm speaking particularly of the versions of these systems in which the "visco elastic" component of the lifter is not adhered to the surface of the ski.

The other evolutionary path I've noticed has been an evolution of the original Hangl carve plate. That plate was in a way an evolution of different features of the Deflex than the route taken by EPBS. Hangl grabbed onto Deflex's use of hard mounting the rear of the plate while using soft points on the front. As Hangl plates have evolved into Salomon's Pe2 binding integrated system, PowerAxe SL, PowerAxe GS lifters and the Pilot system this concept has remained as a constant (except in Pilot). Through the use of selected "visco-elastic" elements these plates/systems have been evolved to harness flex energy from the front of the ski to release it at completeion of the turn in varying degrees depending upon application. In the PowerAxe race plates the enery return is very aggressive with the GS allowing little flex in the system and the SL allowing more. Crossmax 10 Pilot and S914 Pe2 systems return significantly less energy than the race plates. Then we come to Scream 10 and Crossmax 8 Pilot and S710 Pe which are only slightly more energetic than two piece bindings. The interesting thing is that the only difference between the Crossmax 8 Pilot and Scream 8 Pilot (prior to 2004) was the viscoelastic pieces in the Crossmax but not in the Scream! The ski and binding construction were identical. At demo the feedback was always that some skiers liked one and really disliked the other.

Anyway, I digress. I guess the thought I had to further this thread is that soft mounting points (screws through keyhole slots) and their location on a lifter or binding can modify the flex of a binding system dramatically. Is this one of the keys to integrating bindings to a ski to create a ski product that works in concert with a particular binding product or to even accomplish the integrated product?

Aar
post #14 of 20
Quote:
Originally posted by Wear the fox hat:

And here comes my crazy idea...
The ultimate binding should therefore be one which only has one interface with the ski, creating a single load point. Create a single mounting point binding and you rule out the issues of inter-binding forces and flexing.

S
I have 2 words for you......Spademan bindings.

One more thought relating to that.... don't.
post #15 of 20
Wear The Fox Hat is right..AND I have a coupla words for you

"Bear Traps"

Now..here folks is a binding with a single mounting point.Those pesky little issues about..you know "pre-releases"..NEVER! ABSOLUTELY NEVER!ditto for phantom releases..

Not only is that little stuff about interference with the ski flex GONE..but with the "correct" boots..even the sole flexes so as not to have that annoying long flat ski boot sole that can cause pressuriziation issues..
post #16 of 20
Me thinks somebody is board, Need to ski more, think less. Has summer really been that long...

PM good lesson but for most of us average skiers, I don't think the intergrated system makes that much of a difference.

I will say that I can tell the difference between settings 1,2&3 on my Marker SC's. I have friends that say there is no difference. I have asked skiers with Atomic bindings if they feel the difference when the change the position of there binding on the ski. Most ask "the binding can move?" "what are you talking about?".

On my Atomic's, I move binding all the time as conditions change.

I've seen people who have new skis every season and still don't know how to ski well. They have all this money to spend on equipment but never take a lesson.

Some people are just there to have fun and watch the kids play or race.
post #17 of 20
PM/Arnold:

Any further experimental results on this thread?

Thanks.
post #18 of 20
PhysicsMan,
Want to take my quantum mechanics class for me??? [img]smile.gif[/img]

MelloBoy
post #19 of 20
Thread Starter 
Quote:
Originally posted by comprex:
PM/Arnold: Any further experimental results on this thread?
Sorry, but nothing on this end. I've been busier than the proverbial one armed paper-hanger.

Quote:
Originally posted by MelloBoy:
PhysicsMan, Want to take my quantum mechanics class for me???
Mello - From your profile, it sounds like you are a grad student in chemistry, so you'll appreciate why I'm going to turn down your kind offer: I had 6 semesters of general QM in grad school. One semester was taught by Ken Wilson (before he got his prize in '82), and 4 were taught by Hans Bethe, who was also my minor advisor in theoretical physics, and who hence took a personal interest in making sure I didn't fall asleep during his 8 AM Saturday morning lectures. Adding in several more semesters of applied QM in other grad school courses like solid state physics, scattering theory, group theory for chemical physics, etc, I've had enough QM to last me for several lifetimes. So, with respect to your offer, thanks, but no thanks.

Tom / PM
post #20 of 20
I think that this is one of those situations where removing the effect of "squeezing the fixed boot/binder assembly" is theoretically going to help the ski flex more naturally, and engineers will have more control etc. But I think the effect is probably negligible in most cases except certain situations like short soft skis with large boots. So I agree the naturally ski flex argument is a paper one.

Being able to adjust for-aft, increased dampening, and larger boot adjustment ranges are some concrete advantages of these systems. But the main advantage is marketing.

Personally I will always ride the look/rosi design cause it is the best binder out there (most elastic travel) and that is something that matters a great deal. I will deal with the fact that my ski's flex is effected like 0.5% by the rigid system that keeps me on the skis when I need to be.
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