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Where is the "real" BOF?

post #1 of 26
Thread Starter 
I'm interested in the BOF method of binding location, but after sorting through dozens of posts here and on Realskiers, I cannot define what is signified by the "Ball of Foot." Since I used to teach anatomy, stay with me through the jargon, try my experiment, and you'll see the practical problems:

1) There is no precise definition in the books. Laymen tend to mean the point where most weight is concentrated when you stand on your toes. This corresponds loosely to the distal ("big toe") end of the First Cuneiform. Many folks have a little bone called the Medial Sesamoid that sits under that cuneiform, so that's about as close to a "ball" as the foot gets. In either case, this is where a majority of the weight finishes when you take a stride and are ready to toe off again; go walk in wet sand to see my point.

2) On the other hand, if you tap the outside of your medial boot shell with a hammer, or otherwise try to locate the bump that projects out medially from apparently the same place, you'll actually be about 2 cm foward of the First Cuneiform, at the proximal joint of the First Metatarsal ("big toe"). When people get bunions, that's usually what's enlarged, for instance.

3) Experiment: From a biomechanical perspective, the weight of your body during a static forward lean - rather than a push off while walking - is distributed along the diagonal line running from the distal ends of the First Cuneiform to the Fifth Cuneiform. Take a marker pen and draw a line on your sole from the "ball" along the comparable joints of all the toes and you'll see what I mean. Now I assume that if you're balanced laterally over your skis, the midpoint of that diagonal, not the "ball" over the First Cuneiform, is where your weight should be. (Obviously, your weight shifts along this diagonal as you tip your skis, but it should average midpoint.) Am I wrong in this assumption?

4) So if you're up for more self-decoration, take a ruler and draw another line that bisects your sole along its long axis into left/right. Where the two lines cross is the biomechanical midpoint. I also assume it's where the BOF balance shown on Realskiers locates the point, since it's semi-dynamic (pivots fore/aft, but not medial/lateral).

5) Notice that this new point is another one to two cm's behind the "ball."

6) Conclusion: These three points vary a lot from foot to foot, and your own may be nearer or further than mine. But the bottom line is that the various ways suggested here to locate the BOF should produce quite different results from the BOF mechanism shown on Realskiers, which already puts the BOF well ahead of the ski midline in some brands. Basically, I think the boot tapping or visual approaches will tend to produce points that are an INCH ahead of the true biomechanical point and two or more INCHES ahead of the boot midline mark. Based on these threads and my own experience, that's a lot.

7) Don't have a clue what this will mean in terms of skiing, but maybe it's worth thinking about. I have RX8's this season, and I'll play around with the locations up to 4 cm each way, see if I can check back with more info. Meanwhile, I'd welcome feedback from the instructors and experts who routinely use this method.
post #2 of 26

A quick trip to Gray's Anatomy and



That about right?
post #3 of 26
Thread Starter 
Yep, thanks for the visual aid. Looks about right. Notice the difference between the maximum bulge of the first metatarsal base (between 1 and 2, if I can read your pic) and the actual BOF (3). So my question stands: What are we locating when we find that bulge?
post #4 of 26

WOW, too complicated.

No technical jargon here (and no confusion).

When I played basketball and they talked about balancing on the ball of your foot in a defensive posture no one pulled out Gray's Anatomy, we all just naturally stood on the pad under the big lump behind our big toe.

When I got drafted into the Army and they taught us how to do an "about face", everyone just used that same part of the foot (this was, after all, the Army so no intelligence was allowed).

When I read Peter's description, I used the same part of my foot. Interestingly, this approach on the boot and the "center of running surface" for the ski EXACTLY matched the +15 setting on my Head skis with Railflex.

KIS-Skier
post #5 of 26
Do the sesamoids not sit under the distal end of the first metatarsal as opposed to the first cuneiform? This would be where I would consider the ball of the foot to be as used in layman's terms.
post #6 of 26
Lateral, intermediate and medial cuneiform bones all articulate with the proximal ends of the metatarsals to form the mid tarsal joint. The ball of foot is located where the first metatarsal head (distal) articulates with the proximal first phalanx bone. Under that joint, the sesamoid bones are located just proximal to the joint spacing.
post #7 of 26
That was my thinking although I have read/heard of experimentation with mounting centre point on speed skis to be lined up a little in front of the calcaneous which would put it pretty close to the line comprex has marked. The thinking there being that in a ski boot this is where the weight tends to be centred most of the time. Don't know what the realskiers site is referring to though.
post #8 of 26
The "rub" here is that this point will migrate when skiers use boots with different forward lean angles and "delta's" will also affect this. Oh I wish this could be easier.... I'm making a device that will determine a skiers
center of weight distribution when all the forward lean and delta angles are present. It should be done by Friday 01/20/06. Oh Yay....more data to pore over!
post #9 of 26
You've pointed out that there are obvious opportunities for interpretation of "ball of foot", but I agree that this is taking things to the extreme. The BoF is not a precise point on your foot, but an "area" that most sports depend on for quick moves and balance. That's the whole point of the BoF mounting method - to get the best balance point of your body directly lined up with the center of the running surface of the skis. I hope that someone develops a new version of the Campbell Dynamic Balancer that will bring this service to the masses, but for now most of us must deal with approximations and crossed-fingers (which is why the Railflex systems and binding plates are good things that allow for adjustment).

If you haven't seen my thread on a new method of doing a BoF mount position setup then please review it. I have found it to be much more accurate - and the magnets are the best part (http://forums.epicski.com/showthread.php?t=33666).
post #10 of 26
Quote:
Originally Posted by cantman
I'm making a device that will determine a skiers
center of weight distribution when all the forward lean and delta angles are present. It should be done by Friday 01/20/06. Oh Yay....more data to pore over!
Interesting. Single footed?
post #11 of 26
Thread Starter 
Thanks for the informed feedback, guys. L7 and Cantman: I misspoke. Sure nuff, my Grants Atlas shows the sesamoid at the distal border of the 1st metatarsal. And your def sounds more reasonable in terms of some radiographs I'm looking at, where the point of soft tissue contact is roughly below the distal end. Call that the BOF. So the difference between that BOF and boot midline mark is even greater than I thought - about 7 cm for my Salomons!

On the other hand, still unclear about how this BOF relates to the actual balance point of CM. It must vary. When we're quietly standing flat-footed, it's shown by the intersection of diagonal and sagittal planes in the Gray's illustration, roughly over the arch. When we're standing on our toes, depending on how much plantarflexion we have (how high on our toes), our real CM will move between the diagonal in the Gray's illustration, and the diagonal started by the BOF. As known by any woman wearing heels. I'd also guess my boot midline assumes a resting flat foot. Wrong.

Or not; off to play around with settings on my newish Fischers. Thanks again.
post #12 of 26
Beyond - If you haven't looked into the Campbell Dynamic Balancer you should really check it out and understand what it brings to the ski/binding/boot balancing of the complex variables involved. Once you're familiar with that then you should check out the special Nordica report on the tests they conducted on fore/aft binding mount positions (available via Realskiers.com). The end conclusion is that the Campbell Balancer is best, but the BoF method is so darn close it probably isn't necessary in most cases. With all that understood you should be less concerned over the dynamic nature of a body's CM and how it relates to the BoF.
post #13 of 26

Wouldn't

A teeter board will take in all the variables and just "feel right" ? I tried the teeter board method in my boots while being fitted for foot beds. At first I was perpexed, but with closed eyes and a sense for my own feet, It didn't take long to get the correct location for the BOF. If the BOF is considered the ahtletic balance point.

In the same way, I felt the middle of the foot was easily located when standing relaxed and erect with the weight distributed "in the middle" of the foot. (Use the 1 through ten method, ten for toes/ 1 for heels, you get the idea!

CalG
post #14 of 26
Quote:
Originally Posted by comprex
Interesting. Single footed?
The measurements will be taken with the skier standing in a semi-neutral
stance, skis on. (I just got in the rest of my test equipment, now onto building!)
post #15 of 26
what i am curious about, since I have a few pairs of skis awaiting being mounted (with bindings for those with dirty minds!) is has anybody skied the same ski/boot/binding combo with the standard factory line mount and then skied the same rig with their BOF adjusted mounting?

If so, was the difference in performance that noticeable?

every time i get ready to buy a new binding or get all revved up to have a pair of skis mounted I start second guessing based on all this overload information I soak up on these forums.

am i really gonna notice much difference between the performance of the factory line and my BOF?

for example, i have a pair of AR5's mounted 0.5 back of the factory line. They are noodly and tend to pull me into the back seat. not having ever ridden them with the bindings mounted on the factory line (or forward of the factory line) i have no idea if that's how this ski skis or if it's a result of my mounting them back of the recommended line.

i guess what i'm saying is, if I go through all the trouble of the BOF measurments, as per Noodler's link, how will i know if it's really worked to my benefit or not (and vice/verse)?
post #16 of 26
Just a suggestion as to how this may playout in reality, assuming that the fundamental issue here is where to locate the binding on the ski. If you can, get skis with demo bindings that allow for fore and aft adjustment and go play with the settings starting with "center of ski/center of boot".

I've long noted that I am most comfortable with the bindings set for "one click" forward of center, additionally when I've let people use my skis I've set them up the same way and they are pretty happy with the setting. To bring this home .... when shops mounted up the identical ski with the center of boot/center of binding; all I heard was "they don't ski as well as the ones you set up" .....

There are many issues of balance and technique or individual ski, but the fore/aft test may just help you to get past the question of how it will generally apply to you.

This week I am taking in my new skis to have them "hard mounted" (not with a demo) and .... I am taking my old skis for them to exactly match the fore mounting position that I favor.
post #17 of 26
Thread Starter 
FWIW, I did the BOF on a pair of Stockli Spirits I'm mounting, found it was 2.5 cm in front of the factory mount line. Which seems in line with what Noodler and others have reported for Stockli's.

In my experience on adjustable Tyrolias, even 1.5 cm makes a noticable difference in performance, and feels distinct from the fore-aft adjustments we make with our bodies. Think about it vis-a-vis racing plates.

My technique was as described here and at RealSkiers: Take the liner out, position the foot equidistant fore-aft in the shell, but touching the medial (inside leg) shell. Tap on the shell until you find your BOF. Mark the boot. Then position the mark at the measured mid-point of the ski's running surface.

Which in this case was a full 7.0 cm ahead of the factory line. (Most of that is made up for by a boot midpoint being 4-6 cm behind a BOF.) Difference in this case, +2.5 cm.

Incidentally, the new transparent shells make this a snap. You can see your BOF, instead of having to tap for it!
post #18 of 26
Is the optimal mounting point at the center of the ski for every ski, or does it vary depending on flex distribution, construction, and intended use? And how does this affect a BOF mounting point?
post #19 of 26
Quote:
Originally Posted by dookey67 View Post
what i am curious about, since I have a few pairs of skis awaiting being mounted (with bindings for those with dirty minds!) is has anybody skied the same ski/boot/binding combo with the standard factory line mount and then skied the same rig with their BOF adjusted mounting?

If so, was the difference in performance that noticeable?

every time i get ready to buy a new binding or get all revved up to have a pair of skis mounted I start second guessing based on all this overload information I soak up on these forums.

am i really gonna notice much difference between the performance of the factory line and my BOF?

for example, i have a pair of AR5's mounted 0.5 back of the factory line. They are noodly and tend to pull me into the back seat. not having ever ridden them with the bindings mounted on the factory line (or forward of the factory line) i have no idea if that's how this ski skis or if it's a result of my mounting them back of the recommended line.

i guess what i'm saying is, if I go through all the trouble of the BOF measurments, as per Noodler's link, how will i know if it's really worked to my benefit or not (and vice/verse)?
I've had 2 pairs of skis where I have been able to compare skiing with mounting based on manufacturer's mounting mark and "BOF" on center of running surface (or my estimation of it). The first was a 175 Pocket Rocket with original bindings mounted per manufacturer. When I remounted them with Freerides I moved the bindings about 2-3 cm form ward. The second was my Metron B5's. With these I've had the binding at the standard and "forward" position. I didn't go farther than the forward position as I didn't feel like there would be enough "tip" left.

In both cases I could easily distinguish between the 2 positions and preferred the forward position. The skis were easier to control and I felt that I didn't struggle with my stance in the forward position like I did in the rear.
post #20 of 26
The best way to figure out what's right for you is to use bindings that permit fore/aft adjustments without re-mounting. You can also consider plates/lifters that are drilled to the ski once and then the bindings are moved on the plates without need for re-drilling (that's the method I currently use for most of my skis).

It's a major pain to have to re-drill skis to figure all this out, but it's not unheard of. I unfortunately had to re-drill my Stockli XLs 3 times - luckily it's a ski that can take it.

We've discussed whether or not you'll notice it many times. I believe you will in at least 10mm increments.
post #21 of 26
volklgirl - your thoughts have been discussed here a few times and we've discussed this issue on-slope many times. There is no escaping that changing the mounting position will also change your relationship to the flex pattern. We're also definitely making some assumptions about the "position" of the sidecut in relation to the running surface length. Skis with radically different sidecut designs (multiple sidecuts designed into the same ski) may actually have their midsole mark "designed" into the ski. In this case a BoF mount may work against the manufacturer's intentions. In general though, this is just not the case.

Overall I believe that most skis handle BoF mounts quite well, but the impact on the flex pattern should be considered. A ski with an overly stiff tail that is remounted 25mm forward may now have a more relaxed tail section. Whereas a ski that already has a softer tail may go a bit too soft even though the sidecut may now work better at the BoF position.

I wish there was more science to this, but dookey's post gets directly to the goal of all this - try a ski in multiple positions and decide what's best for you. That's what the top level racers are doing and I believe it will work for most recreational skiers too. The question is whether you have access to the resources to make it happen.
post #22 of 26
"The question is whether you have access to the resources to make it happen."

BINGO!

I posited this same question on another thread about boot fitting and tweaking. A number of the folks on that thread were professional boot fitters with free access to the equipment so they could tweak the fit, hit the slopes, tweak some more, etc.

A regular joe like me would end up spending buko dinero to do all the tweaking that was talked about on that thread.

this seems a little less money intensive, but more "labor" intensive. and again, relies somewhat on having the resources (and time/inclination) to undertake such an endeavor.

i haven't had much problems with the factory recommended lines yet, so I don't know. Maybe I'll notice something this season if I am able to eclipse 39 day on the slopes.

one thing I am a bit curious about. I have the Railflex system on a pair of No Ka Oi's. The shop told me that they can be moved +1.5 / -1.5 in either direction. I keep reading people talking about being able to move them 3cm either way. Now 1.5 + 1.5 does equal 3, but everything I've been told by the shop where I bought them is taht I can't move them +/- 3. Just curious how folks are moving their Railflexes back 3 or forward 3 (or are these folks using demo bindings).

That brings up another thing. In order to get a binding that is flexible in terms of moving it (other than the plating suggested) one would have to go with a demo binding, which we all know are heavy as hell. Is the ability to finagle your mounting point worth the extra weight?

Finally, what is the effect of a plate on a freeride or powder ski (say like a Mantra or a Spatula)?

Final finally, where does one obtain the information of recommended factory mounting points for various skis? For example my Karmas have an "I" on the sidewall, but also a "Freeride" denotation on the topsheet. Conversely, my Titan 8's have a barely visible mark on the topsheet, but it's tough to tell if it's the factory mark or part of the topsheet design.

Whew!
post #23 of 26
Karmas usually have a second "FS" mark on the topsheet, hidden under a sticker. I used the "FR" mark myself. I also put Tyrolia RailFlex bindings on them and my new Atomic Sweet Daddys in order to allow for some adjustment as needed, and to share bindings between the two skis. The Karmas feel fine on center; I haven't skied the SDs yet, but like knowing I can vary the position around if I need to.

The people speaking of +3 on the RF are probably locating the aft mount point on the ski center mark, and then going to +1.5 (center) or +3 (forward) with the other points. You can also adjust the position by stepping front and rear pieces along the center bridge, so many different adjustments can be made beyond the normal +/- 1.5. Just make sure the heel and toe pieces are still on the track!

The RFs do add some extra weight, but not enough that it's an issue to me (some of my other ski/binding combos weigh more). I do think there are potential downsides to a plate that offers flex and rise on a park or powder ski. For dedicated powder use, the flex is not real important and may alter the ski's response a bit. For park use, neither flex or rise is desirable because it can make the skis more clumsy underfoot. For my all-mountain usage, however, plates for flex and rise have been just fine on the Karmas -- no bad effects detected, and I appreciate the convenience in mounting and positioning the bindings.
post #24 of 26
Here's Peter Keelty's article on ski binding placement
http://www.techsupportforskiers.com/..._placement.htm

He says, "One manufacturer's spokesman (since moved on) actually came clean and corroborated our skidding theory.

His intriguing response: "Yes, we do place our athletes near the center of the running surface, and yes, our retail models place skiers farther back, but we don't want to give recreational skiers too much tail. They lean on the fronts of their boots to pressure the tips to enter the turn and can't handle increased tail length."

"In other words, the rearward position makes it easier to skid and all but impossible to develop more modern carving technique.

"Worse—since most skiers, goes industry thinking, skid turns, making it easier to skid will lead skidding skiers to conclude they are actually skiing better. It's called "Take the Easy Way Out Marketing" in our book.

"And, of course, there's a chicken-or-egg aspect to this. Are recreational skiers leaning on the fronts of their boots because they want to, or are they forced to do so to make skis with these rearward mounting marks work?"

This makes movable bindings from Atomic, Tyrolia (who else?) a very good idea.


Ken
post #25 of 26
All of last year I was batteling on the masters course way below my own level. I was using a pair of Head iSL RD 165 for SL and a pair of Head iRace 177 for GS. At the end of the season I borrowed a pair of FIS Blizzard GS skis and I was totally blown away. They were a little longer, 181, than my overcut GS skis but turned as easily and had way more edge hold and carved like a dream. I started to compare the skis at home in my garage and soon found out that the bindings were positioned much further in front than the bindings on my Heads. This fall I then stumbled onto the BoF discussion and did some new measurements on my skis and found out that the Blizzard (I had taken good notes) bindings were placed exactly at the BoF/CRS position. I now took the old plate off and swapped it for a VIST plate mounted the plate and bindings 40mm further in front to match the BoF/CRS mark. I know form looking at them that this is a 100% improvement. With the bindings in the old position I had a hard time carving all the way through the turn. At the end of the turn they were running wide. With the Blizzards this did not happen. Same thing with the SL skis. As soon as I get my knee in shape Im going to test the skis and see if my theories are correct or not.
post #26 of 26
Quote:
Originally Posted by dookey67 View Post
one thing I am a bit curious about. I have the Railflex system on a pair of No Ka Oi's. The shop told me that they can be moved +1.5 / -1.5 in either direction. I keep reading people talking about being able to move them 3cm either way. Now 1.5 + 1.5 does equal 3, but everything I've been told by the shop where I bought them is taht I can't move them +/- 3. Just curious how folks are moving their Railflexes back 3 or forward 3 (or are these folks using demo bindings).

That brings up another thing. In order to get a binding that is flexible in terms of moving it (other than the plating suggested) one would have to go with a demo binding, which we all know are heavy as hell. Is the ability to finagle your mounting point worth the extra weight?

Finally, what is the effect of a plate on a freeride or powder ski (say like a Mantra or a Spatula)?
First of all the Railflex has a 3.0cm range comprised of 3 positions over +1.5cm, 0, and -1.5cm. Where you mount the rail will determine if you'll be able to pull off a +3.0cm from the manufacturer's midsole mark.

Many people assume that when "plates" are mentioned we're talking about the original plates that were developed for WC racers. Today there are many, many plate choices and many of those choices do not radically affect ski characteristics (no change in flex, ride feel, etc.). I almost prefer to call them "lifters" since the term plates has a negative connotation in some people's minds. I definitely don't recommend added lift in the park-n-pipe scene, but I don't feel there is anything negative about lift (when the amount is used with discretion) for all-mountain duties.

More and more demo bindings are getting better and better. I noticed that through the last round of demos this season. There are many that are not nearly as "clunky" as they used to be - so I wouldn't automatically dismiss all demo bindings.
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