Info for smart ski buyers: Bearing surface discussion
Posted 1 year, 5 months ago by Seth Masia
Here’s an issue you rarely hear the big factories talk about: Bearing surface. That’s the area of base plastic in contact with the snow, and it has a direct effect on the way a ski feels in powder.
A typical narrow straight ski (take for example the 1995 Rossignol 4SV, 203cm, 64mm waist) had a bearing surface of about 1150 square centimeters. If a 165 lb. skier stood on one ski, the pressure underneath would be about .14 lb per square centimeter.
Doesn’t sound like a lot. But the 1990 Atomic Powder Plus — the first of the superfat powder skis — had a bearing surface of about 2000 cm2. A 165 lb. skier put about .08 lb./cm2 on that ski.
Neither of these skis is very versatile. They lie at either end of the soft-snow performance spectrum: the Rossi slalom ski was designed for hard snow and in deep snow liked to go to the bottom and stay there. The Atomic was famous for bobbing around on top, denying the skier one of the great pleasures of powder skiing, the face shot.
If you live to porpoise in and out of deep snow, you want something midway between these extremes. For resort skiing, with a firm surface under the new snow, you may be comfortable with a pressure pattern of about .11 or .12 lb/cm2; for backcountry and bottomless powder, .9 or .10 lb/cm2. For that 165 lb skier, this would imply a bearing surface around 1400 or 1500 cm2 for the resort ski, or 1600 to 1700 cm2 for bottomless snow.
There’s a set of simple formulas for figuring out bearing surface based on length and sidecut dimensions, but as a rule of thumb, with today’s sidecuts, at a length of 165cm, a 70mm waist will give you about 1200 cm2, 74mm is about 1300cm2, 80mm is about 1400cm2, and 90mm is about 1500cm2. If you need more surface, you’ll need to go longer, Big Guy.
Seth Masia
Vail Ski School
Permalink · Posted by Seth Masia · October 16th, 2008 · · Read 9 Comments
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October 16th, 2008 at 9:38 pm Pete Wagner
Will skis with a similar flex pattern and similar bearing surface feel the same even if they have very different dimensions?
For example, will a 165cm with a 80mm waist (and roughly 1400cm^2 bearing surface) have the same stability as a much longer and skinnier 180cm ski with a 65mm waist (that has a similar 1400cm^2 bearing surface)?
October 16th, 2008 at 9:59 pm Seth Masia
Great question, and the answer is no, they won’t feel the same. To get the same bearing surface, the ski with the narrower sidecut is still going to need a wider tip and tail (in spite of the additional length). When you calculate it all out, the longer ski with the narrower waist winds up with a deeper sidecut and slightly shorter turn radius.
Because it has a more radical sidecut, in powder the longer ski with the 65mm waist will sink deeper at the middle and the tip and tail will float more. You’ll have more trouble bringing the middle of the ski back to the surface, and a lot more trouble pivoting the ski because there’s more resistance at the ends of the lever (the longer ski). It’s going to require better edging and balance skills, in both soft snow and on firm surfaces. In fact, with an appropriate flex pattern, the longer ski is not a powder ski at all, but a radical carver — something midway between a modern World Cup slalom or GS ski. I wouldn’t take it anywhere near powder.
October 17th, 2008 at 10:18 am Ryan
Seth…………. what was the 1st short fat ski that you, Tommy Lippert and I skied down Poulsen’s Gully at Squaw???? Short, fat, no shape lots of ‘rocker’? I called it the ‘Looney Tune’ ski because I felt like a cartoon character on it.
WE all agreed that it was a ski-like experience…. on the mashed potatoe snow, the skied stayed under us ………. but/and it was a ’slappy’, bouyant experience ………. rock-a-belly, rodeo.
How did bearing surface relate to that ski? Hmmmmmmmm… was it an Atomic?? same era as the Kastle ‘Big Foot’.
October 17th, 2008 at 8:53 pm Seth Masia
Kathy, that day we had a couple of pairs of the very first superfats — I think we had the Atomic Powder Magic (later the name was changed to Powder Plus because Kneissl had a trademark on the Magic name), and probably the Lacroix of about the same shape — they were cafeteria trays. They didn’t really have rocker — it’s just they were so wide you never really got them on edge. The had the “standard” sidecut of the era’s straight skis. Also, they were mounted assymetrically, with the bindings closer to the medial edge. This forced you to ski a kind of one-footed schmeared intermediate technique instead of weighting the feet evenly.
The Bigfoot, BTW, was a Kneissl. The next year we got the first Kneissl Ergo and the original 203cm Elan SCX GS ski, and the 90mm Atomic Guide and Volkl Explosiv. The shorter toon skis arrived a year later.
Seth
October 18th, 2008 at 9:28 am Ryan
Thanks Seth………… so there really wasn’t a flex pattern to those skiis, and floatation…. was what it was about? Did those skiis have a huge bearing surface? and as you mentioned no sidecut……….. yes they were cafeteria trays.
Going full circle………. technique was extension / retraction (up and down)……… and we only sunk about 5 inches in the crud.
Assymetrical mounting……….. didn’t several manufacturers try that with their boutique skiis? Kept tuners active.
That was the same year we put modern bindings on old skiis. Am I recalling the results of our research correctly??? …. Equipment does affect skiing style…… or how we look skiing under the chair, and how much energy it takes to make a turn.
;>) Ryan
October 19th, 2008 at 8:07 pm Pete Wagner
Seth – How does assymetric mounting affect things?
October 19th, 2008 at 8:45 pm Seth Masia
Asymmetric mounting is when you put the binding closer to the medial (or inside) edge than to the outside edge. When a ski is wide enough, putting the binding in the middle won’t merely disable the ski brakes — it will also force you into an exaggerated bowlegged stance.
The first generation of superfat powder skis, based on the original Atomic Powder Magic, had a 115mm waist. The binding was mounted closer to the inside edge. This meant it was practically impossible to load the lateral (outside) edge of either ski. If you edged the right ski to start a turn to the left, you could unweight the left ski but it was pretty tough to load the left edge of the left ski. This forced you to do all the work with the outside ski, unless you were skiing a more-or-less skidded intermediate technique with the skis fairly flat on the surface of the snow — which is how most people skied these.
It was quite different from the polished evenly-weight, simultaneously edged technique developed by expert skiers using GS skis in powder. But it opened deep powder to intermediate skiers and saved the heliski business from bankruptcy.
Seth
November 10th, 2008 at 8:40 am Jon
quote: 1600 to 1700 cm2 for bottomless snow
I guess most of the skis designated for really deep powder like the fat LINEs, Lotus 138, Völkl Kumo etc. have way more bearing surface than your suggestions. How come you see a 165cm/90mm ski suited for deep pow, whereas some people think 185cm/120mm skis are alright for pow.
One of the Wagner skis referrals (Sven B.) also got a pretty wide ride designed for him…
November 12th, 2008 at 7:05 pm Pete Wagner
Jon – When designing Wagner Custom skis we pay a lot of attention to people’s favorite skis and/or skis that they’ve been riding recently. We also pay a lot of attention to terrain preferences and where the person skis. This information generally drives where we go regarding width.
So, a person who’s been enjoying a DPS with a 138mm waist and skis in the Utah backcountry will get a dramatically different design than someone who been skiing on a 75mm waist on-piste at Vail.