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Ball of Foot Center of Running Length

post #1 of 22
Thread Starter 
Is there any reason why you would not want to mount a binding to match the center running length of the ski to the ball of the foot?
post #2 of 22
Powder skiing. Generally you'd want to be back from that point a bit.
post #3 of 22
Yes. If you don't LIKE being mounted way forward on a ski then it would be inappropriate. Some skis feel good forward some don't. It's personal preference. In my opinion, manufacturer's do a pretty good job finding a point that works for a wide range of people... and there really isn't a huge range of foot sizes that normal adults have. You can say most adult males boot lengths will fall between 285mm and 335mm, thats 5cm. A wide range, right? Wait. The mid point divides the difference in 1/2 so, 25mm. But the 'BoF' isn't the end of the foot, it's about 1/4 of the way back... so 1.25cm. That's 12.5mm for 95% of the males that ski, that's not really that much variation. Manufacturer's get pretty darn close for most people.
post #4 of 22
WR, that is a very good generalization worth keeping in mind -- I agree 100% that once you settle on the proper midsole mark, there's only 1-2cm of variance in that for the range of boot sizes. It may not pay to fiddle around in many cases. I think you added some good reality to the debate.

Ultimately though, I think it depends on where the manufacturer puts the midsole mark relative to the center of running surface -- the mark itself might not be where I'd want it. Some brands tend to go way forward (Elan) others tend to go way back (Atomic). When using the midsole mark, I have been as far forward as +2 from BOF and as far back as -6cm from BOF; both cases felt wrong to me and ultimately a re-mount was in order. So I always check this before mounting skis and take it into account, along with the desired purpose of the ski. I want to be 0 to 1.5cm back of BOF/CRS in most cases, and if the manufacturer's midsole mark puts me there, perfect.
post #5 of 22
Why would the ball of the foot mean anything anyway? That is NOT the point on the foot which matters. Nor is the actual running surface.

The ski is designed to have the tibial axis mounted almost directly over the narrowest point on the ski. Do you suppose this is coincidence?

The more time you spend on the ball of the foot, the more time you will spend beating yourself up, trying to make the ski work the way it's designers intended.
post #6 of 22
Thread Starter 
There seems to be as many different schools of thought. From the research I have done and upon the advice of Pierre, mounting BOF/CRL is usually a desired method.

I did it on my RX8 and the mounting point was 2.5 cm in front of the standard mounting point. I found the ski performed best mounted forward. I just got a pair of Cool Heats and the mounting point ended up only being 1 cm forward(at the most).
Quote:
Originally Posted by vail snopro View Post
Why would the ball of the foot mean anything anyway? That is NOT the point on the foot which matters. Nor is the actual running surface.

The ski is designed to have the tibial axis mounted almost directly over the narrowest point on the ski. Do you suppose this is coincidence?

The more time you spend on the ball of the foot, the more time you will spend beating yourself up, trying to make the ski work the way it's designers intended.
post #7 of 22
Quote:
Originally Posted by vail snopro View Post
Why would the ball of the foot mean anything anyway? That is NOT the point on the foot which matters. Nor is the actual running surface.

The ski is designed to have the tibial axis mounted almost directly over the narrowest point on the ski. Do you suppose this is coincidence?

The more time you spend on the ball of the foot, the more time you will spend beating yourself up, trying to make the ski work the way it's designers intended.
vsp, I haven't heard of the tibial reference before -- can you elaborate?

The BOF method focuses on putting equal amount of ski running surface fore and aft of the point at which you would rotate a ski. We tend to do the rotation about the BOF, not about the heels, not about the toes, not about the midsole. So the BOF is a logical point to line up with the center of the running surface. I doubt it's perfect, but it comes close to the way we rotate a ski down through the foot.

As far as I know, the BOF method has nothing to do with the way we should put weight on the ski (ie, forward, ball of foot, backseat, etc). It's not about the vertical loads. BOF mounting is about putting a yawing/turning input into the ski. It makes the assumption that the skier has the proper fore/aft balance independently.
post #8 of 22
Quote:
Originally Posted by vail snopro View Post
Why would the ball of the foot mean anything anyway? That is NOT the point on the foot which matters. Nor is the actual running surface.

The ski is designed to have the tibial axis mounted almost directly over the narrowest point on the ski....
Yeah, please elaborate. Links would be nice too.
post #9 of 22
I'm curious about how boot length effects the mounting point. Ie. if you have big feet it seems you may want to be mounted back a bit? All the structures of your foot will be larger so it would seem that that center mounting could push the ball to far forward (despite boot center being in the right place).

I just got a new pair of skis (mounted on the line) and they seems to feel a bit like I'm having to turn them with the arch of my foot rather than driving with the ball. I wear a size 12 (mondo 30). The shop's going to let me take out the demos pair of these skis and move the bindings around on the demo track before I do a remount, so hopefully that will clear things up a bit.
post #10 of 22
This is a no brainer, guys (gals)!

It is simple biomechanics and equipment design. But it will also take an opening of ones mind and the willingness to challenge ones previously held belief system!

Lets start with a short Equipment 101...

Why does everybody now refer to whatever ski they are on by its dimensions? I mean- "my ski is a (64, 85, 110) underfoot" always referring to the narrowest point. Well, sportsfans, the narrowest part of the ski is NOT mounted under the ball of the foot! So, question- if its not under the BoF, then where is it and why would I want to stand on a part of the ski which is wider? Once again, if your skis are mounted correctly, the narrowest part will fall under the back half of the arch/ front half of the heel. (pretty darned close to being right under the tibial axis!) Again I ask if you think this to be coincidence?

Go ahead! Take your favorite pair of skis and measure them! Unless you have disregarded the Manufacturers Mounting Specs, I can tell you right now that the narrowest point will fall nearly under the point I have referred to! In fact, it could be that for those of you who have modified the MMS, and have found you really like it, maybe you have put yourself even closer to my expectations!

To really make the ski work the way its designers intended, you need to be balanced over that narrowest part of the ski. This leads us to.....

Biomechanics 101-

Since I specifically mentioned the tibial axis, lets find out why!

Lets NOT turn this into a 'we do/we do not' turn our legs thing, ala the paralysis by analysis forum. At least for the moment, lets just accept that something happens and the femurs DO pivot to some degree in the hip sockets.
As all movements transmitted from the body to the skis are via the legs, lets take a closer look at these incredible devices! Geez.... where to start? There is so much bad info being circulated by hearsay and 'common knowledge'. Well, this is where I'm going to challenge your belief system.

The neutral stance is NOT on the BoF! The center of any rotation is NOT the BoF! At least not if you expect the ski to carve or hold on the hardest of conditions! The neutral stance is under the tibial axis!... Here's why!

Lets start with something very simple and obvious. Stand with your feet in your normal skiing stance width. Balance on one foot, so that you may manipulate the other while it is on the ground. Twist the light foot, with it's pivot point being the BoF as some of you have suggested. What happens to the heel? Hmmm...., ya...., you are right! It displaces laterally! Yes, if extrapolated out as if you had a ski on, that is a heel push or a skid. And for the leg to twist with the BoF as its center of rotation, also makes the leg displace, not being a pure pivot at the hip socket. It becomes a circumduction movement.
Now, lets try this again, only using the tibial axis as the pivot point. Yup, no leg displacement! What you are now enacting is more of a slicing action of the ski on the snow. With 2/3 of the ski in front of this point, that leaves much less ski to displace and skid. But now you will say, "but the tail of the ski will still displace laterally, just less of it"... If it displaces, you are right.... LESS of it will! Hmmm... less displaced= less skidding= more carving= better edge hold! Sounds like a winner to me!

But I'm not done!

"What else do we have for these nice people, Johnny?"

"Well, Ric, we are going to blow up one of the greatest fallacies in skiing!"

COOL!

How many of you are aware that if you are levered forward to the point where you are balanced on the BoF, you have reduced the range of movement which edges the skis by about 50%? Can you still tip them somewhat? SURE! But anything more than this limitation is done by tipping your entire body into that movement, something which may not really be so great, especially in really hard or difficult conditions!

Try this instead. Once again, identify your tibial axis. Now go ahead and put all your weight on that spot. Flex your leg (ankle, knee AND hip), and tip the leg as if you were engaging the edges. The range of movement, and the freedom of that movement should be quite noticeable, as compared to what you feel while balancing on the BoF. The feeling of control and power while balancing over the tibial axis should be incredible compared to the wishy washy feeling of balancing on the BoF.

What it comes down to is this. So many skiers are trying desperately to create edge angles or to carve their skis, but are in a completely inappropriate stance to achieve this. The harder they try, the less effective they become! But this comes from too many "skilled" skiers advocating something which they have no real understanding of, but rather, are merely perpetuating the fallacies which have become accepted gospel over the years. (Look at how long it took to get past the idea of "sitting back in powder")

If it doesn't feel strange, you aren't making a change!

For many of you who have never experienced this position may feel that you are too far back, or that you are sticking your butt out. While these may be the feelings, that is only because its new to you. In fact, you have now found a true neutral position! This should become your new benchmark! Other movements are acceptable, so long as you always return to this neutral point.

I wish I was some sort of video/computer geek who could diagram or somehow show exactly what I'm talking about in this medium. But I'm not, so I hope my descriptions have at least piqued your curiousity and given you some insight into how elite skiers do ski.

I don't normally get involved in the gear discussions because the crap is usually so deep! I prefer to wear my waders when fishing, not when sitting at a keyboard. If you are wondering if I know what I'm talking about, go ahead and ask. I'll fill you in on my background which, though I haven't written a book or created a teaching system, is substantial.
post #11 of 22
I like my skis mounted aft boot center.. Loved my Atomic gs12 which was about 1,5cm back and don't love my fischers as much at factory boot center.. Way too forward for me, I think..
post #12 of 22
VSP, that's pretty clear.

I see that circumduction in everyday walking.
Obvious in sandal wearers whose heels slip off to the inside of the sandal.
post #13 of 22
I've had a lot of Atomic bindings which allowed for and aft movement, and generally like them centered, but really don't notice a huge difference.

I picked up some Salomon Scrambler customs cheap, thinking they would be a good AT ski....light, fairly wide for me, good amount of sidecut, which I like, pre-notched tail for skins.

I hated the skis, They turned effortlessly in powder, but hooked if you had any decent amount of speed. I ski powder in an old school turny style, but these things were ridiculous.

I figured before I tossed them I'd try moving the bindings back. The Naxo holes would allow redrilling at either a half inch or an inch an a half. I went big----they are so far back the tips drop on the lift. Guess what? they ski much better, on powder and groomed. I actually like the ski, and can haul ass and drive them now, something Salomons aren't known for.
post #14 of 22
vsp, I think I am following you and am in agreement, but a cartoon would help. Never mind fancy graphics, you could draw something on paper and take a picture of it if it got the point across.

I am with you on the notion of pure rotation through the tibial axis, versus rotation and displacement through the BOF point. For all I know, lining up BOF with CRS may in fact be putting my tibial axis over the narrow part of the ski, but that needs to be checked out. Anyhow, why the focus on the narrow part of the ski lining up with the tibial rotation? You wrote:

"To really make the ski work the way its designers intended, you need to be balanced over that narrowest part of the ski."

Why do you think this the case? What is it about the geometric waist that becomes important in your argument?

And to skip another iteration I'll ask my followup -- generally it's the sidecut that determines the turn shape/size of the ski, more specifically, the combination of tip, waist, and tail dimensions and the length of the running surface. Why the focus on rotating about the waist when a solid carve turn engages the whole edge, and the combined sidecut specs (as a unit) govern the shape? Why would you not be focusing on driving/rotating the sidecut as a whole? (which sort of brings us to center of running surface as a possible/logical point of symmetry for rotation).

Thanks.
post #15 of 22
Hey VSP,

As you know, I don't dispute your tibial axis theory. I do have some questions though...

Would the flex pattern and torsional rigidity come into play to effect how a skier might perceive these different mounting points? Or, might a ski be designed such that applying load a bit ahead, or a bit behind, of the narrowest point would result in uniform contact along the length of the edge due to the characteristics build into the ski?

Could adjusting the mounting point provide a means of compensating for mismatch of skier and ski, for a skier with inappropriate technique, or for particular stance/balance bias, etc? ...might a light skier prefer a more forward mounting on a stiff ski etc.

You spoke of Equipment and Bio-mechanics, and never mentioned the ski boots that connect skier to ski! How can you ignore ski boots in this equation? You acknowledge that it is common understanding that neutral balance is BoF. If that is the case, wouldn't it be common that a skiers boots are balanced so they find neutral fore/aft over the BoF? ...and if so, wouldn't they have to have their boots re-balanced or make compensatory movements in order to move their balance point back to the tibial axis you suggest? If making movements to compensate, then wouldn't this compromise their stance and ability to create edge angles as well?

As long as you have been in the industry I am sure you have heard of the Campbell Balancer, yes? See this study:
Is the Campbell Balancer an Effective Tool for Determining Ski Binding Position

If I gather correctly (from the "discussion" section), their results indicate a corrected mean difference of 3.2cm preferred forward mounting determined by the Campbell vs that of the factory. I follow your bio-mechanical explanation, however, it suggests loading the ski aft of where many commonly advised. Yet this study seems to indicate a preference of moving a binding mount forward and this is consistent with my recollection of anyone I have talked to that has done the Campbell Balancer. (However, unless I'm missing it, the boot lengths of the testers is not revealed to determine where they balanced underfoot.) Nonetheless, do you have any thoughts as to why skiers would prefer a more forward mount of their bindings if the ski is designed to be loaded aft of where most skiers typically attempt to balance, before moving further away from that ideal point?

If there is in fact a correct location under foot that our balance should be centered over. Pick one, BoF or tibial axis. Why is the Campbell balancer used to determine movement of the binding? Why wouldn't you balance the skiers boots, so that they are balanced over this ideal point? Wouldn't they then be able to click into any bindings set at the factory mounting point (or with the BoF over CoRS if that's your poison) and be good to go?

Thanks,

Chris
post #16 of 22
VSP, I’m pretty sure that, skiing, like walking, skidding on a slippery surface, skating, or running, involves a dynamic change in the COM from behind the support structure (trochlea of the talus) to in front of it. In a normal resting stance, in fact, the COM is slightly in front of the tibial seat of the talus. This reflects the reality that our feet evolved to walk, not stand (or ski). At both heel strike and toe off, the plane of the tibia is much closer to the BOF than it is at rest. Put another way, our bodies are designed to want to fall forward.

Even if you assume the older model of an inverted pendulum, the COM is constantly moving forward past the tibia during any forward movement of the whole body. Yet you seem to assume either a static location of the COM exactly over the tibial shaft during all phases of the turn, or that COM has no relevancy. In reality, I’d suspect that the position of the BOF reflects an average of where the COM is during rapid forward body movement, and I’d question whether the tibial axis of rotation is the entire story here.
post #17 of 22
I would expect to find that most of us who have experimented with binding placement have estabilished a general tendency one way or another for most skis in most situations (exceptions aside), each will find what works for them. This preference would not only be a product of one's taste or skiing style but would be governed by each ones weight distribution.

I'm big all over... wide shoulders, barrel chested, wide waist, big glutes and oversized thighs. Undoubtedly my Center of Gravity is going to fall aft of someone with a narrow waist and smaller lower body so my anatomy dictates the forward position whereas another will require the center or rearward position. So the end result is getting the weight to the same place on the ski even though the final position of the binding may lead us believe otherwise.

Hey, maybe that's why the guy who invented the Cambell Balancer (I'll bet his name was Cambell ) invented the thing. Since I'm running short of Cambell Balancers lately if I don't like how the ski handles I just try a different position, and go try it, so far I always wind up spot on the BoF.

Steve
post #18 of 22

Just wanted to say, finding where is the balance point improve my skiing a lot thanks vail snopro.

post #19 of 22

BOF is what you BALANCE on as a skier.  Its about CENTERING there - so you want make sure you are on the optimum spot.  Thar happens to be the center of the running surface.  Keep it simple folks.  Get CENTERED and stay there in ALL skiing conditions.  You will find your technique wont have to vary much at all to adapt to the changes

post #20 of 22
Quote:
Originally Posted by cgeib View Post


As long as you have been in the industry I am sure you have heard of the Campbell Balancer, yes? See this study:
Is the Campbell Balancer an Effective Tool for Determining Ski Binding Position

That link appears to be broken, try http://lous.ca/newsite/wp-content/uploads/2013/09/nordicareport.pdf
post #21 of 22

What are we to make of the fact that with rockered tips the center of the running length changes depending on how much on edge the ski is and on whether one is skiing packed or powder snow?

post #22 of 22

Intersting stuff mr brain cheat.  I have noticed that Nordica recommends a position farther back than ball of foot (BOF)@centre of running surface (CORS).  The reasoning I heard was that recreational skiers cant stay on edge all day long like the shaped carving skisi demand so they allow for some skidding in the turn by positioning  bindings farther back.  Its a marketing thing.  I mounted some Nordica GS race skis to BOF@CORS as I thought the recommended spot was too far aft, and they ski great.  Just mounted some Elan SG 211cm race skis for my son and the Elan manufacturers midpoint for the boot (measured from the tail of the ski) put his BOF very close to the CORS.  Its been my experience that it varies between manufacturers quite a bit.  Rossi/Dynastar have been close to BOF@CORS by my calculations.  I think you need to measure it out and do the math before you just accept the manufacturers point for mounting to avoid disappointment.  This is where a pre-drilled plate comes in handy to save the remounting, as would a rental binding, allowing for easy experimentation

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