Skis and Gear Discussion > Gear Garage

Re: New Approach to Binding Mount position; split from Stockli Laser SX review.

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HighAngles:
I thought the binding mount position thoughts brought into the ski review worthy of it's own thread.
I usually find my eyes glazing over, but this I understood.
Would love to hear more thoughts  from the forum.

Lynn



Nice to hear that you found the sweet spot on the Laser SX.  Quite frankly, the Laser SX is about as kick-ass as skis come.  It's on my buy list and I'm actively looking for a good deal on a pair (170cm).

I had an interesting chat with HH at short turns camp regarding binding mount position.  I was already leaning in this "new" direction, but HH has absolutely confirmed my current thoughts on the correct mount position.  I started out using the BoF over center of running length and that evolved to the BoF over center of effective edge, but I started realizing that the point I was finding to work really well for me also corresponded to have the boot midsole aligned with narrowest point on the sidecut of a ski.  Without any real "prompting", HH said that this was also his experience and he explained that when you think about what happens when a ski is flexed into an arc, having the boot midsole at the narrowest point is the only mounting position that really makes the most sense.  So I have gone back through most of my skis to double-check where my boot midsole sits in relation to the narrowest point of the sidecut and amazingly they almost all are dead on. 

I'm going a bit further now, with the hypothesis that when your BoF lands on the center of effective edge AND the midsole mark on the boot also lands exactly on the narrowest point of the sidecut, magic happens.  The skis that I own that match this criteria are the ones that I feel are completely dialed in for me.  This clearly plays into the ski design arena and I wonder how many ski builders are aware of this relationship when designing the ski geometry.

Svend:
Great review - thanks John.  I have read a number of reviews in the European German-language media about the Laser SX, and they all rave about this ski.  Your comments re. binding mounting point seem to similar to my experience on the Stormriders that I tried last season.  I had to get waaay forward over the shovels to make that ski work, and the bindings were clearly mounted too far back.  Interestingly, the shop mounted them at the BoF/CRS mark.

HA - you make a distinction between BoF/CRS and BoF/effective edge.  What's the difference? I have never heard of a reference to effective edge.  Furthermore, how are you determining the narrowest point in the sidecut? Seems to me that there might be a significant portion (couple of centimeters at least) of the ski that would measure almost the same dimension using an ordinary ruler, at least with my middle-aged eyes squinting at the little marks.  Do you use a micrometer?

HighAngles:
Svend - thanks for the interest and here's more detail on the subject since Lynn has so nicely broken this out into its own topic. ;)

For years and years (long before we had factory mounting marks on skis and boots), skiers used the Ball of Foot (BoF) positioned on the Center of Running Surface (CRS, aka midpoint of the running length) when mounting their bindings.  Even after we got the factory mount mark on skis and the boot midsole mark, some skiers still preferred to go with BoF on CRS.  Of course this was before ski sidecut geometries and tip/tail profiles got, let's say, "interesting".  With dual sidecuts, early rise tips, and full-on rockered 5-point designs, BoF on CRS no longer produced the desired results (since determining CRS becomes quite problematic).  There has also been some confusion/controversy over how to properly determine where the BoF point really is on your foot and where that point is positioned inside the boot shell.  For the purpose of this post it's not necessary for me to get into the details of those issues.

So BoF over CRS evolved into BoF over CEE (Center of Effective Edge).  The Effective Edge length is the distance from the widest point of the tip to the widest point of the tail.  What makes CEE slightly tougher to determine is that it's the length "along" the edge, not the chord length between the two widest points.  IOW, you need to use a flexible tape measure to really do this right; to determine the midpoint between the widest points of the tip and tail.

Unfortunately even BoF over CEE fails with some of the more modern takes on ski design.  Some builders do some strange things with the positioning of the ski sidecut and also their new takes on ski rocker profiles.  That's where simplifying the whole process by just aligning the boot midsole mark over the narrowest point of the sidecut makes a lot of sense.  For this to really work well though, I would recommend that you have a fairly close fitting boot so that the midsole mark on the boot actually corresponds to the midsole point of your foot.

The best method I've found so far to determine the narrowest "point" on a ski's sidecut is to use a digital caliper.  Use the caliper to find the approximate narrowest point along the sidecut and then lock the caliper's measurement adjustment (usually there's a thumb screw to lock the jaws in place).  The narrowest waist measurement will sometimes occur over a "range" in the middle of the ski; possibly for 2cm or more. This can be handled by taking the locked calipers and marking the forward and rearward points where the locked calipers "catch" on the ski (slide the calipers through the narrow range and mark the forward and rearward points).  With those points marked, measure and find the midway point between them and mark that point as the narrowest point of the sidecut (basically it's the middle of the narrowest range of the waist found).  The main problem with this method is keeping the calipers square to the center line of the ski while taking the measurements.  I'm still working on a type of jig that can make this process faster and more accurate.

Svend:
Hmmmm....very interesting subject.  For years I used to do the BoF/CRS thing on all of my family's skis, and then found that on some skis this just didn't create a sense of a balanced stance.  Either the tails were washing out, or one would have to get way forward to get the tips under control and to engage.  So I have almost abandoned this method due to too many instances where it simply didn't work -- my wife's im78's, her Progressor 8's, my Progressor 9's.... The final straw came when skiing the Stormriders last spring -- as mentioned, the shop set them up for my friend at the BoF/CRS mark (Knee binding, flat mounted), and it was simply a terrible spot to mount them - felt like it was about 2 cm back of where it should have been.**  The shop owner, who is one of the boot fitters on Epic, has long been a vocal proponent of this method, and was punting it to my friend as the magic spot on the ski and the only way to find a mount location.  So much for that theory.  ::)  They were almost unskiable.

This is no big deal for skis with adjustable bindings or plates, as I have simply moved the binding until the skier feels centered and balanced, and the tips or tails are well weighted and under control.  But for skis that are flat mounted this is a real dilemma.  I have been at a loss to find another method to find a balanced stance, as I am understandably reluctant to go back to the shop for repeated re-drilling.  Both of our daughters have twin tips that are flat mounted, as are my wife's Dynastar all mtn. skis, and I guess I have been lucky that the BoF/CRS seems to have worked well for them - the skis handle well, with no apparent issues - but they are all traditional camber and sidecut geometry.  However, our youngest is nearing the point when she will have outgrown her Fischer twins and will be ready for a longer ski.  Those that I have been checking out for her all have at least early rise, if not some tail rocker too, and I didn't know where to start trying to find a good mounting mark on those, so I had been planning on getting a plate or rail type binding.

Skier stance likely plays a role in this too, I would imagine.  My wife, for example, has as her natural stance a rather forward, low and aggressive position, brought about by years of power skating since childhood.  Our daughters, OTOH, are much more upright, albeit still driving the shovels with shin to boot tongue pressure.  But their fore-aft weight balance is clearly going to be different over the skis.  In your experience, does this have any influence on where your final mounting mark settles? Have you set up skis in this way for others, or just your own? In other words, have you mounted according to measurements, only to find that it didn't work for a particular person because of stance peculiarities?

Overall, though, your description of CEE and narrowest sidecut point are extremely interesting.  Encouraging, too, that I now have a real alternative to finding the correct mounting point on a rockered and/or multi-sidecut ski, leaving the option of a flat mounted binding still open.  You've piqued my curiosity, and I am going to do some measurements of our own skis to see how they line up.  My P-9's would be a good candidate, and my wife's iM78's.  I don't have a digital caliper, but I do have a micrometer that might serve for now.  Re. midsole mark on the boots, I'm not sure if your criteria for a tight fore-aft shell fit is the same as ours, but all our boots are 1/2" to 3/4" gap at heel, toes touching, on a footbed.  Hopefully that matches well to the mid-foot spot.

Thanks, H-A.  Great post.

**Correction: I just re-read my own review of the Stockli's, and found a note that, while the bindings were indeed set up at the BoF/CRS mark, there was also a riser plate of 8 to 10 millimeters thickness placed under the toe piece, but not under the heel.  This would doubtless have influenced my impression of the bindings being mounted too far back. 

jim-ratliff:
H-A:
Postulate a little bit along the lines of Svend's line of thought. The mount point for women skiers is generally accepted as being farther forward, and the distance between the BoF and the center of the boot is also generally less because of shorter boots.
Would you adjust your approach for women (or for taller than average guys with longer feet)?

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