VERY generally speaking, the bindings should be mounted so that the ball of your foot (BOF) is directly over the midpoint of the ski's running surface (the part of the ski that contacts the snow when it is flat with weight applied to it).
With apologies to Peter Keelty for cutting and pasting this from his excellent website, I'll give you the following exerpt. I do this to encourage you to go to his site Tech Support for Skiers
and sign up as a member. There is a plethora of information there about ski gear, and a very extensive article on binding placement. the cost is minimal, and well worth every penny if you're any kind of gear geek (and YOU are).
I hope it's OK for me to do this. If not, one of the moderators should delete it.
This is a snippet from Peter Keelty's site:
5 - Binding Placement III (conclusion)
This is the final installment in our binding placement series.
Rather than blather on about results of the binding study to which we refer in parts I & II, we herewith post summary results of the actual study. (click here for printable version)* Warning; some parts of this are heavy going, but the conclusions are of special interest.
* requires Adobe Acrobat reader. Download for free here.
Our own conclusion is rooted in the real world, recognizing that manufacturers are delivering skis with predetermined mid-sole marks and increasingly with plates that accept only that brand's bindings, or with built-in tracks?skis like Atomic's Device models?or with bindings that are built into the ski, like Volkl Motion and Piston Motion Models, Salomon Pilot and Elan Fusion models. Your choices are becoming increasingly limited, but there are some choices left:
1. On skis with no plate, track or built in binding, skiers may prefer the binding position determined by using the BOF method (which, alas, is technically demanding, requiring that a top-notch technician who serves the race community determine mounting position, as well as time consuming and expensive.) Better yet, and harder to find, work with a shop that has the Campbell Balancer.
2. There may not be an issue to begin with. French ski companies, along with K2, Stockli and Volant, place mid sole marks relatively farther forward than do most Austrian and German manufacturers and so drastic fore/aft adjustment is likely not needed by most skiers.
3. Atomic and Tyrolia make bindings, the Variozone and Super Railflex models, respectively, that can be skier-adjusted fore and aft to find the most comfortable position. The most comfortable position is the one in which the ski seems easiest to control in the widest variety of conditions. Hard-core powder hounds may prefer mounting positions relatively farther back than short radius, fall line fans.
Our conclusion remains unchanged from previous articles, to wit, that in the end it is up to the individual skier to determine his or her sweet spot. Remember, too, that there are hundreds of thousands of skiers having fun off-the-shelf recommended binding positions.
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BTW, there is also a good explanation there on how to accurately find the BOF on your boots. Peter's site is the best site that I know of (other than EPIC of course) to find unbiased information on ski equipment, and invaluable if you're an eBay ski buying junkie like me. [ September 16, 2003, 10:08 PM: Message edited by: Carvemeister ]