<decided that this now needs to be first and it has been edited for clarity>
EDIT P.S. - I have decided that this method does NOT work with funshape/5-point designs. I believe that it can work well for traditional, multi-radius sidecut, and early rise designs.
In the last few years it has become readily apparent to me (and others) that the current thinking revolving around BoF (Ball of Foot) over CRS (Center of Running Surface) mounting point determination was incredibly inaccurate for today's advanced geometry skis. With skis sporting dual/triple radius sidecuts, klothoid designs (Palmer), early rise, rocker, and full-on funshapes (S7, Wailer 112RP, Obsethed, JJ, etc.) trying to use the CRS in any determination of the mounting point is an exercise in futility.
So here I present my latest incarnation of determining a binding mount position based on placing the BoF in an ideal location on the ski - hopefully on the sweet spot for you. I hope that this thread does not devolve into an argument about the merits of BoF mounting positions versus the manufacturer marks. That has been done to death. What I would like to see is an intelligent discussion regarding the merits of this process (both pros and cons) from those who advocate or are at least interested in the concept that there is no one single mounting point on a ski that will work for every person's morphology.
As a refresher here is what I'm currently doing to determine the distance from the BoF to the midsole mark.
Determining the BoF to Boot Midsole Mark Adjustment Length:
- Stand on a hard surface floor in your bare feet.
- Go up on your tip toes (only your toes and BoF are in contact with the floor).
- Slide a thin business card along the floor up to your foot from the rear.
- The business card will stop where your BoF meets the floor.
- Lower your feet being careful not to shift the position of the card.
- Use a pen and mark the point on your foot where the business card edge stopped.
- Measure the length of your foot (this could be done on a Brannock or carefully by backing your feet up to a flat wall and marking where your toes end).
- Find the midsole of your foot (half the length) and mark this position on your foot.
- Measure the distance from your BoF mark to the foot's midsole mark.
- This value is your BoF to Midsole adjustment (for me this is 56mm).
Note that I use a digital caliper for the measurements and it can be helpful to have someone assist you in placing the business card and getting your foot measurements, as trying to do these measurements yourself can slightly alter the true values. Also, I should point out that I have a VERY tight shell fit now (dropped down another shell size). My foot is literally exactly the length of the bootboard and I have about 5mm shell fit. So my foot's midsole is very close to corresponding to my boot shell midsole mark. There have been plenty of other methods published on how to find your BoF and figure out where it hits in your shell (i.e. the shell tapping with a hammer method, etc.). Just note that your foot is never "seated" in the middle of your boot when you're buckled down - it's always pushed to the rear, so any "free" space in the shell length fit is mostly in front of your toes and would need to be accounted for in determining your own BoF to Midsole adjustment length.
Now we move on to the significant change to the previous method of determining the binding mount position. There is a summary of the steps below for those who wish to ignore the detail of the method and how I arrived at devising it. Instead of using CRS I am now using the Center of Effective Edge (CEE). My reasoning is basically this - what amount of the ski surface that rides on the snow when it is flat is of little consequence. I started wondering why we would even care about a flat ski. What we're really after is how the ski acts and reacts when we have it on edge. Considering the ski when it's on edge has the effect of "equalizing" some of the more complex designs available. I'm certainly not going to say that this is a cure-all and infallible for every crazy design out there. I haven't done nearly enough testing to hang my reputation on that shingle. What I am saying is that using the effective edge of the ski will result in a more realistic determination of a mount position based on how skis are actually designed to be used - on edge.
After deciding to go with Effective Edge, I researched exactly how the EE is determined. Unfortunately I ran into many opinions on what constitutes the Effective Edge and how to determine it and measure its length. True Effective Edge as I understand it is the length of the edge that can come into contact with snow in a turn and be utilized - generally hardpack is assumed. However, most manufacturers that do list EE (including many snowboard makers) use the absolute extreme value for EE found when the ski/board is 90* on edge. I don't know about you, but I never get my skis to 90* on edge . So that left me in a position of having to decide just how much edge angle to assume when developing the new method. I settled on 45*. You may argue that it really should be 60* (for very aggressive racers who regularly achieve high edge angles) or some might say 30* is more the norm for the recreational skier. I don't know. I decided to go with 45* and see how well it played out on my own skis.
Then I had to figure out a method to determine and measure the Effective Edge at 45*. I decided to go with two 45* wedge wood blocks. My blocks are about 3" thick and about 5" tall. They are positioned on a fairly level flat section of the floor and the ski is positioned on them so that the ski bases rest on the 45* angle of the blocks. This simulates a ski on edge at 45* that has NOT yet been decambered. This is key. I decided not to mess around with decambering skis as that would lead to inconsistent results due to that variance in being able to decamber a ski consistently to the same amount. I also reasoned that the edges are beginning to engage while the ski is still cambered and as pressure is initially being applied. So why not just go with the ski in its "natural" form?
So with the ski resting against the wood blocks I once again use that thin business card and slide it between the floor and the ski coming in from the tip and from the tail. Where the card stops is then marked on the edges of the ski at the tip and tail. Note that the resulting marks are very different from what you would arrive at in determining CRS. To measure the Effective Edge length I use a flexible metric tape measure. I chose to go with flexible tape since it can closely follow the actual edge to determine its length. A standard metal tape measure would result in measuring the chord length between the marks would introduce some additional error.
With the length of the Effective Edge in hand, the midpoint is easily determined and then marked on the ski. This is the new spot where we want to position our BoF. So from this position we measure rearward by the amount of our BoF to Midsole adjustment value. This position is the new calculated midsole mark to be used when mounting the binding.
Calculating the Ski's Custom Midsole Mark for Binding Mounting:
- Position the 45* wedge blocks on a fairly flat smooth floor.
- Strap the ski brake and place the ski against the blocks so that the base is resting against them with the ski sitting at a 45* angle.
- Make sure that the ski base is consistently in contact with the wedge blocks across the entire face of the blocks (no gaps).
- Slide a thin business card in from the tip and then mark that position on the ski edge. Do the same for the tail.
- Using a flexible tape, measure the length between the tip and tail marks DIRECTLY along the edge. Do not stretch the tape between the marks (aka chord length).
- The value obtained in step 5 is the Effective Edge length taken at 45*. Divide that value in half to find the midpoint and mark it on the ski (this is the CEE)
- From the CEE mark measure rearward by the amount of your BoF to Midsole Mark adjustment. Mark this point on the ski.
- This final mark is your new calculated custom midsole mark that will be used for the binding mount.
Interestingly enough, on "standard" skis, traditional sidecut and camber, the position determined by the new CEE method almost exactly corresponds to the mount position determined using the older BoF over CRS method.
Please note that I strongly believe that this method results in a STARTING POINT for coming up with your ideal mount position. It is not an absolute. Only further experimentation will confirm/deny that the BoF over CEE method has provided the best mounting position. So you may ask yourself why bother at all with all this insanity? I would say because you have to start somewhere and personally I do not trust the manufacturer's mark as a starting point due to my long history with testing binding mount positions and almost never ending up using the manufacturer's mark.
I will provide additional posts regarding my own skis, where the marks ended up, and how the testing went. I need to re-energize my batteries before continuing...
Edited by Noodler - 12/19/10 at 6:00pm