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HOWTO: Mount Alpine Skis Using The "Ball Of Foot at Center of Running Surface" Method
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December 17, 2010
1:43 am
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You might think that ski manufacturers would have some standard for determining where your feet will stand on your skis relative to their length. As far as I can tell, you would be wrong, because they vary dramatically...and manufacturers will even vary the recommended mounting point from year to year!

  • Mounting bindings too far forward on a ski makes it feel "short" and unstable for its length, makes skating awkward, and possibly increases the risk of ACL injury.
  • Mounting bindings too far back on a ski makes it feel "long" and sluggish for its length, decreases rebound, and when taken to…
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February 12, 2011
6:28 am
Colin Stone
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Hi,

I've had a look at Sal Lord 177 and Sal Amber Origins 158.

From the ski specs the Lord mid sole mark is 791mm from the tail. The white line across the ski is only 770mm from the tail when measured with a straight tape, 772mm if the tail curvature is followed on the top sheet and 777mm when measured along the base. I have also attempted to measure the centre of the running surface (CoRS) along the ski. This comes out at 89mm ahead of the white line, or at 859mm from the tail. It is probably incorrect as the skis have rocker.

I have also checked the boots which have a nominal BSL of 297mm, actual measurement is 295mm. The position of the ball of my foot (BoF) is approx 40mm ahead of the mid sole mark at 147.5mm.

On the ski, the BoF is approx 810mm from the tail and 49mm behind the CoRS, possibly incorrect.

On the Amber origins, there is no mid sole mark. Using boot MSM, the mark is 635mm from the tails. The CoRS is 45mm ahead of the MSM, and just about ties in with the BoF. The BoF is then 680mm from the tails and Sal quote 686 for the MSM.

Perhaps Sal MSM quoted measurement is actually the BoF??

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February 9, 2014
4:59 pm
Barry N Thom
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Thank you very much for clarifying the ball of foot and centere of running surface, this is how i have imagined the correct boot positioning to be, now all i need is a mechanic to put my boot where i want it!

ATB Barry

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February 10, 2014
8:34 pm
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Barry:

It's always worked for me.  Given that a correct stance should position your weight directly over the ball of the foot, BOF/CORS makes sense.

If you want your skis mounted forward or back, it's best to clearly mark, on the ski, where you want the midsole BEFORE giving your skis to the shop!  In my experience, directions like "I want these skis 3cm forward" often get lost in the shuffle.

Of course, I now mount all my own skis in order to avoid such problems.  If you're comfortable with a drill -- and ready to assume liability for your own mistakes -- go here for paper templates that will make the process much easier.  (Hint: it's best to practice on a pair of dumpster skis before mis-drilling something brand new that you just spend $600 for.)

JS

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April 8, 2014
2:15 pm
Peter Summers
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I own two pair of skis: The Völkl Mantras and the Völkl Ones. The bindings on both skis are mounted on the Völkl reference line. The Ones ski great, but on the Mantras I often find myself leaning back in the boot to make the them go faster. Would moving the bindings a bit backwards help me get a more neutral to forward stance? Any help appreciated.

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April 10, 2014
2:56 am
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Peter:

I'm not sure about "going faster": it mostly has to do with balance in a turn.  Try sideslipping straight down a flat, steepish groomer: if your tips tend to hang up more, you might be too far back, and if your tails tend to hang up, you might be too far forward.

JS

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December 28, 2014
8:54 am
apingaut
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This is a nice, thank you.

Question. Have you ever tried to sort this out for a ski that has rocker?

I am measuring a ski that has a combination camber and a good amount of tip rocker. I measured CORS and Center Of Side Cut (measured the same as CORS, not center of radius). There is 12cm between these two points on the ski with CORS closer to the trail and COSC

It turns out the factory mark is 1 cm behind center of the two (+5cm CORS -7cm COSC). Not sure if this was intentional or not, I haven't measured rocker skis before.

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January 2, 2015
11:42 pm
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apingaut:

Rockered skis can be tricky, which is why I add the "Caveats" section in the article.

Briefly, the problem with rockered skis is that they can have two radically different measurements for running surface, depending if the snow is hardpack or soft.
* On hardpack, the measurement is made as above.
* In soft snow, the running surface extends forward and backward into the rockered area, by an amount that depends on the depth of the snow and the contour of the rocker!

Let's take an example of a ski with a 30cm rockered tip -- i.e. it's 30cm from the tip of the ski to the forward contact point on hard snow. A typical non-rockered ski will have perhaps a 15cm tip -- so this means the front contact point in hard snow is 15cm behind the contact point in soft snow! And, effectively, the mounting point of the ski, relative to CORS, will be approximately 7.5cm forward on hard snow vs. soft snow! This means the behavior of the ski should change dramatically in hard vs. soft snow...

...and I have found this to be the case. In the real world, I dislike skis with lots more tip rocker than tail rocker...they feel too far forward on groomers and too far back on hardpack, and if I mount for one condition they feel either sluggish or skittish in the other. I prefer skis with nearly symmetrical rocker -- no more than ~7cm of tip rocker in excess of the tail rocker.

Back to your point: "center of sidecut" is usually close to "CORS on soft snow", so mounting midway between "center of sidecut" and "CORS on hard snow" is probably a good starting point. Thank you for suggesting it!

JS

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