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# Powder Skis And Skier Size

### The science of ski floatation explained by our expert Physicsman

Photo by Bob Peters

## Contents

Skier Size and Optimal Ski Width

Ski Width, Snow Depth, and Floatation

What Qualifies As Powder?

## Skier Size and Optimal Ski Width

We should be careful about extrapolating from one's own experience using normal width skis in soft snow when making ski recommendations for people of substantially different weights. Here's why:

Let's assume that there is some validity to the oft-heard claim that mid-80's skis are the best thing since sliced bread for average weight guys (say, 175 lbs) in soft snow. Then, one can estimate the width of a ski that would give the same amount of float to a skier of a different weight. Here's a table that does this:

 Weight (lbs.) Width of ski (mm) 100 49 120 58 140 68 160 78 189 87 200 97 220 107 240 117 260 126

Thus, if you are a little slip of a 120 lb woman, you will have the exact same float on a 58 mm wide pair of skinny boards that Mr. Average Guy (at 175 lbs.) has on his 85 mm "lite-fat" skis.

Basically, on any sub-70 mm ski currently being sold (because they are all greater than 60 mm), Ms. 120 Pounder will sink in less than Mr. Average Guy on his Rex's, so its to be expected that a light weight person might not fully appreciate the need for fatties (at least from direct personal experience).

At the other end of the spectrum, a man weighing 210 lbs. will need to be on 100 - 105 mm boards to achieve the same float as Mr. Average Guy on his sticks.

Bottom line - guys, especially big guys, have a valid point in wanting to be on wide skis in soft snow. And, to head off any comments, yes, we have all skied powder in 207 cm long, 64 mm straight sticks from the past, so fatties are not absolutely required, but sure are fun and make marginal snow much easier.

## Ski Width, Snow Depth, and Floatation

Folks thinking about making their first purchase of a wider than normal ski repeatedly make statements such as, "I expect that this 82 mm wide ski should be 'good enough' for foot deep snow".

The problem with this expectation is that soft snow skiing is a lot like water skiing. Specifically, for a given speed, you and your skis won't start lifting you up unless the upward force that the snow exerts on your skis exceeds your weight. So, a 200 lb guy going 25 mph may get 150 lbs of upward force from 70 mm wide skis, and his skis won't lift off of the hardpack base.

Assuming the lift force is proportional to area of the skis, on a pair of 90 mm wide skis (same speed, same angles, etc.), his skis will be generating 192 lbs of upward force and hence, they will still be sitting on the hard base under the soft new snow. However, as soon as he gets on a pair of 95 mm or wider boards, they will generate 203 lbs (or more) of upward force, and his skis will be able to lift off of the base layer and rise through the soft layer.

Thus, this skier will hardly see any change in float from 70 mm to 90 mm wide, then, all of a sudden, at 95 mm, he will start to experience a change in sensation and mode of skiing. This is precisely why many folks (particularly, those over, say 180 lbs) feel that mid-fats are "Jack of all trades, master of none", and why I object to the statement that mid-width skis are "good enough" for a foot of snow. If they really are "good enough" (ie, wide enough at your weight) to float in a foot of snow, they will float in a meter of snow.

This is also why many folks advocate bypassing the mid-fats and going directly to fats. It is also why lighter weight folks get enough float out of mid-80's skis and like them. To them, mid-80's are "fat" skis (at least in their behavior, if not actual width).

Now, obviously, the above description is a simplification. Skiers don't all travel at precisely one speed, and snow compacts, so new snow just above the hardpacked base will be more dense than snow near the surface, particularly if it has aged for a bit. This means that for real skiers in such snow, the transition from not-floating to floating will not be as abrupt as I described above. It will be more gradual with respect to changes in width, speed, and other variables, so mid-fats will actually float a bit better than 70 mm wide skis, just not as much as most skiers seem to believe.

## What Qualifies as Powder?

Width really makes skiing possible when we enter the realm of wind buff and breakable crust. If you break through the surface in these conditions, disaster can quickly ensue. A heavy skier, or lighter skier moving fast making high angle turns, is at considerable disadvantage in breakable crust, but can get floatation with a wide enough ski. For me, the magic width in these conditions is over 100 mm at the waist. A frustration for me this past winter was learning my V-Mantras (94 mm) intermittently and unpredictibly broke through the crust; but taking out a pair of Gotamas (110) in the same conditions solved the problem (but left me looking for more stiffness). I can ski light powder on any width ski, but dust on crust, breakable crust, and variable crud really calls out for a tool that can produce a predictable amount of float and stability.

## Powder Skis and Eastern Skiers

Previously, the discussion centered around the observation that for a skier to rise upwards in a layer of deep soft snow, the skis must produce an upward force (i.e., “lift”) greater than the skier’s weight. Thus, to realize the full benefits of purchasing fatter skis, heavier skiers (say, heavier than 180 lbs) shouldn’t stop in the traditional mid-fat range (mid 70’s – low 80’s), but go all the way to 90+ mm skis.

It recently occurred to me that there is yet another fallacy embodied in the oft-heard statements about not considering any ski wider than a mid-fat, e.g., “82 mm should be good enough for an east coast skier.”

Skiers thinking about buying a pair of fatter skis will often say that since they only see a couple of deep snow days per season, there is no reason for them to go beyond mid-fats. The real problem is that most of these folks make this statement even though they already own a quiver of groomer skis that are perfectly adequate for several inches of new snow, i.e., the usual snowy day in the east. Thus, they really only need a new pair for those rare days when it dumps a foot or more, or for soft, deep spring slop. It almost like these folks think that there is some sort of algorithm that says that for every soft 12” snow day per season you encounter, you are allowed to add a mm to the width of your new skis, but you shouldn’t go beyond this width--or else!

It just doesn’t work like this. If you are in deep soft snow, it doesn’t matter whether this is the only time you will see such conditions this season, or it’s the 40th time. It’s still deep soft snow. Thus, skiers who follow such reasoning and who don’t even bother looking above mid-fat widths when thinking about purchasing a new pair of skis will likely see limited benefits from their new skis in exactly the conditions they bought them for, particularly if the skier is of above average weight. Yes, an 82 mm pair will be somewhat better in soft snow than the 68 mm pair they already own, but the overlap in performance envelopes is greater than it needs to be. In other words, they could do MUCH better than this.

In defense of those skiers who don’t consider skis wider than mid-fats, I do see one valid reason that a 180+ lb guy might use a mid-80’s ski: Namely, that they just never intend to use more than that one pair of skis, at least on any one day.

I would argue that if a skier can bring two or more pairs of skis to the mountain, and has the possibility of selecting the appropriate pair in the morning, or switching skis during the day, their second pair should be 90+ mm skis (at least for skiers > 180 lbs) and forget about the mid-fats. This way, they will get the benefit of fat skis when they need them instead of skiing on a pair of mid-fats that are not particularly good either on the groomers or in the deep.

By the way, when I refer to a fat ski, I don’t mean a specific number of mm. Rather, I mean a width that allows the skier to float given their weight and typical skiing speed. This might be an 75 mm ski for a 120 lb average speed skier or a 150 lb hot-shot, or a 95+ mm ski for a big guy that likes to ski at moderate speeds. This is why I always paired mm with weight in the above post.

Read the forum discussion for more background.

Good stuff. I was skiing heavy wet snow recently on older carvers 68mm at the waist. When slow they were extremely hard work and whenever I was brave enough to go faster they did reward me with a surfy feel. I reckon there was a mid speed range where they felt great, turny and surfy at the same time
This is so cool. I took your method and became an increadable powder skiier up in the north west. Im 220 6ft level 2-3 skier. I always had trouble in the trees in 2-3ft of fresh powder. The only way I could get a float with 82mm was mach snell and thats no fun in the trees. I went out with this info and picked up a pair of EP pros at 128mm waist. WOW what a differance. I can ski slow moderate or fast in any depth powder and turn like im on a groomer with race skis with these!! i went over kill on the float because i wanted to be safe in the trees. I can just gently float and do what ever I want now. Thanks for this info!! I also went 115mm JJ,s for my 16 year old and he skis powder effortlessly also now at 200 lbs 6.1. My doughter is 5.3ft 130 and a racer. Im getting her some 90mm Line Celeberatys this winter for powder days and she can use her race skis for other conditions. This really works!! If you want to float at any speed even standing still go just over these recomendations. More best versatility in one ski stick to the chart. My eps with slight camber accually carve not bad on soft groomers at 127mm under foot. Not like the Jetfuels at 82 but pretty good if the snow is soft.
I went from a 82 waist 193 stiff as iron powder ski, to a 100 waist 186 (twin tip, almost center mount) decently stiff powder ski this year. I ski fast and dont ski trees much, and these skis made a MASSIVE difference, before when I was kicking my way through the snow to try to get on top, im now floating and can turn with ease. Im a bigger guy at 6' 215 and your science works. I stay on top of the crust now, and I dont have to straightline the entire mountain to get the skis off the hardpack.
Quick question, does rocker help float, or just assist turning in the fluff? Could we get an explination of the effects of rocker in soft snow? I don't ski rockered skis as I see the rise as lost edge in hardpack, but maybe you can change my mind, or agree with me. Excellent article.
I am 165lbs and typically ski pretty fast but I like to make a lot of powder turns when I have the chance. I don't really understand the new school make 3 turns per run on powder days mentality. I grew up skiing heavy PNW powder on GS skis. I find that skis much over 100mm to lack any kind of 3rd dimension in power, they stay on top and I loose a portion of "powder experience". I have 66, 68, 98 and 112 waist skis in my quiver. I actually have a lot of fun with the 68's in the powder (until my legs give out) but the turn radius is a bit short at 15 so they occasionally get hooky but most days I opt for the 98's.. The 112's are great in tight trees and drops but don't sink as much as I like. I've been using 100'ish skis for several years now on most powder days but should I add a pair between 68-98mm waist an a longish radius? I tend to look at them as do everything ok but nothing well compromises but maybe I am missing out...
My last experiences with so called "mid-fats" were 2007 Volkl AC4's (82mm) and 2002 Stockli Stormriders (73mm) that were fair at best in these conditions. I have fond memories of some 200cm RD's (the red ones with no graphics) on deep powder days in the early 90's.
This is interesting. Question: On your chart, are you factoring in ski length? If so, how? I'm sure you can see the question behind the question: Heavier people tend to be taller, and in any case tend to ski longer skis, which therefore would have more surface area for a given width.
This article is making me nervous I am 5-10 230 pound X football player just purchased 98 waist skies for powder days in Utah. The shop said that the 98 would be the best for knee deep powder as well as the groomers

You lost me with "...upward force that the snow exerts on your skis..."
The physics of that is lost on me.
Wolfpack. At your weight 98 mm should handle the groomers as well as the powder you'll experience at a ski resort just fine - although they may be a bit of a beast in the moguls. With a one ski quiver there's always a trade off. A 98 mm underfoot skis will be the jack of all trades but master of none. That said, I'm your weight and I'll often use my 78 mm underfoot skis on powder days at ski resorts. They work well when it comes to skiing the powder snow that's on top of groomed runs. However when I'm catskiing off piste, I'm always on much fatter (123 mm underfoot) skis.
Those who claim to prefer skiing "in" the pow versus "on" the pow are looking at it all wrong. Even the fattest floaters sink, just less. Sinking less leaves more energy for vision and enjoyment of the day.
Dick Dorworth had that revelation in his story, Ski Good or Eat Wood.
skiingaround, Google "Newton's 3rd Law of Motion." "For every action there is an equal and opposite reaction." PM is talking about the reaction force of the snow surface.
Wolfpack,
I'm 6' 5", 220 lbs & I think you'll have a much easier time in deep and/or heavy snow with a fatter set of boards. How often do you ski 8+ inches of powder or crud?
I recently went from a 108-waisted 181 cm ski (I know, a bit short for my size) to a 120-waisted 191. I like to ski fast off piste & I really prefer the extra float & stability of a wider, longer ski. If you don't ski at high speeds in deep and/or heavy snow, you'll be just fine with those.
If you do happen to be at the mountain on an epic pow day, demo some fatter skis & see how thay stack up against your present ones. I still remember the day I demoed Icelantic Shamans at Wolf Creek after struggling though a couple feet of heavy powder with my old sub-80-waisted skis. It was an epiphany for me - I discovered how effortless, fun and fast powder skiing could be on the right boards.
Thanks, makes me feel better I do plan on moving into a wider ski next year to add to my quiver but would like to stay married this year so I better hold off. Do you live in the Ogden area? I skied Wolf creek (if the same Mt. last year when the little one wanted to get one more extra day in of skiing during our trip last year. We have season passes to Snowbasin this year. any new snow in the area? I see it in the forecast but the webcams have not looked very good.

Great writeup. I've known why fatter skis float in powder but never really saw a chart for it and correlating sizes, though I know it's just a sensation. I still remember riding on my old Rossignol VAS stright 198CM skis. great on groomers but after a run or two in powder, both me and my dad hung up our gear and went in (not a lot of disposable income as I was in HS at the time and dad was supported the family so never had money for rentals and such, plus he always said carving skis would just be a fad haha). My dad busted his skis and we found a great deal at Sports Authority on the skis they have (living in the midwest but they were good for what we wanted).
Picked up a pair of Rossi Axium STX's that while still narrow with a 68mm waist were at least wider in the tip and tail. First time we went out and skied powder with them, we both came down with grins across our faces. They still sunk but were worlds better and easier to ski than before. Just picked up a pair of Rossi Sickle's this year and hoping to get at least one good powder day while we're on vacation. I've always had the idea that while one of anything (be it ski, car, computer, etc) can be fine across the board, it'll never meet your expectations during those few cases and I've always felt that spending the extra money and getting two or three things that excel at specific tasks and are usable across the board are much more worth it.
Good information. qcanoe raised a good question above that the article did not address. Where does ski length fit into the equation? A longer ski provides more surface area and thus would contribute significantly to the total upward force generated by the ski. I believe I have the perfect width ski for my weight {84} but the 168 cm length, after crunching the numbers, does generate sufficient upward force to keep me above the snow. I believe the 175 cm offering would provide a much improved experienced in 20 cm+ of new snow.. On the positive side the shorter ski is an excellent all mountain east coast ski {groomers, bumps...crud...chopped powder..}. Some of the mid fat skis out there today ski so well on groomed snow that one could easily get away with a mid fat all mountain and a fatter ski for heavier snow days...
Thanks for the analysis, which is one of the best I've read since "The Physics of Skiing." Inevitably folks get into the "My Volkls are better than your K2s because the tails are stiffer" and so on, but the underlying physics is the same.
I've had a long love affair with powder skis, beginning with the K2 Big Kahuna way back when. The recent evolution of powder boards has been amazing. I've loved my Gotamas, but the "insults of aging" (less muscle mass, less energy) pushed me to look for an even wider powder board. Why? To lessen fatigue and thus extend the play time in powder.
Obviously, there are many fine choices. I finally went with the 2012 K2 Pontoon (189mm @ 134mm underfoot). These skis basically ride on top, champagne powder or otherwise, and are adequate for return trips to the lifts. The ease factor: amazing. I personally would not recommend riding the Pontoon and similarly sized skis in new snow that's significantly less than a foot deep. I popped for Marker Schizo bindings, but see now see no reason to need adjustable bindings. Super-wide brakes are needed, btw. The primary "cons" are (a) heavy, heavy and (b), despite the manufacturer's claim that the ski is heaven for all, they are super fast and poorly suited to non-carvers.
Dminus and other posts hit the nail on the head with surface area. Because the skis are shaped with various widths messuring surface area is hard. But if some one had a simple area calculation that would be cool. Rocker also is not factored in the width chart. These numbers are general but do provide a good place to start Ive found. Ive since gone down to a 112 from 128 waist width and found they ski poder great and have less of a trade off on piste. At 220 Im really leaning to even less width with more rocker. the Wailer 99 for instance i tried floated me just fine in bounds off piste.The trade off for groomers was a nice feeling other than ice. ice requires 95 or less I feel to make proper edge contact with min effort. My 112 Faction 3Zeros thow can rail the efford tipping them on edge is a lot compared to my 84mm Nordicas that just rail thinking about it. What would the surface area be useing an average from the waist width along the whole ski. 100mm x 185cm? The tips and tail really are the widest part but are only that. At the very tip and tail. How much rocker would subtract from the surface area but aid in the floating by ramping the forces upward. Most ski shop guys dont take the mass your trying to float. They go by what worked for them. So if the guy is your weight then great. Other wise try before ya buy on a powder day if possable.
I am 5'7"  155 lbs I have some rossignol   B4 s    94 MM  waste They do not float at crystal mountain in heavy snow , Matter of fact , I tried to gain speed and they submarined  . It was a flap on my face , I was leaning back .Trying to stay on top , They work well in less than 6 or 8 inches of powder , But wet powder doesn't work ,The skiiers at crystal that were moving along had some really fatso's on , And some had  what looked like reverse camber . However the article makes a very good point . Mid fats are not powder skis and they sort of overlap Groomer skis any way , My Atomic smoke Blackeye Ti  Does ok in mashed potatoes and aa few inches of powder or crud , , Which means I could just stay on the groomed hard pack where they perform ,I agree the Mid fat rosi really was a waste of my time , Except in the spring afternoon at crystal , Then I could hit a rock and not care , I definetly need a reall powder ski ,
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