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High-speed skiing - Page 2

post #31 of 67
A few years ago at the Prater Cup (J4 JO’s) in Crested Butte, they had a speed trial for the final day. These 13 and 14 year olds were clocking from 55-65+ mph. Measurement was with a speed gun.<FONT size="1">

[This message has been edited by edgreen (edited August 27, 2001).]</FONT>
post #32 of 67
My favorite event in the world, the Prater! I loved taking a group...best part, the terrain race!
post #33 of 67
How did we get from skiing a "blue burner" by an intermediate who makes a turn every five second, I'd guess, to speed skiing at 105 mph?

If you are an intermediate skier, do this test: grab a pole, preferable an old one, but do not put the strap around your wrist.
Sit in the passenger seat of a car and put your arm with the pole out the window. Have a driver go various speed 15-35 mph and touch your pole to the pavement and see if it feels anywhere as it does in skiing.

While making turns, even if the fall line phase (or just after) clocks at, say, 25mph, at the finish of the turns when the pole plant takes place, 15mph is more likely.

Now someone going 35 mph on a steeper blue run is not turning much out of the fall line and thus plants his pole at high speed.

Try it, you'll be surprised

post #34 of 67
Mr. Gonzostrike (I am assuming you are a man),

You do a fair bit of cycling. On a 4% grade you could easily do 35 on your bike. Why is it a wonder that a good skier can do the same on a something far steeper?

What price freedom
dirt is my rug
well I sleep like a baby
with the snakes and the bugs
post #35 of 67
>>> Why is it a wonder that a good skier can do the same on a something far steeper? <<<

Though I'm not Gonzo, I'll state the obvious: skis are sliding (dragging) and bikes are rolling. There is umpteen times the drag on skis than on the ball bearings of a bike.

post #36 of 67
i also haven't been able to find the pedals on my skis yet.
post #37 of 67
You haven't been looking hard enough.
Most skis come with clipless pedals
:} and are activated by pressing the second letter in the skis name.

Yes I agree the drag on skis is greater than drag on a bike but few roads hit a 10% grade which is about a 6 degree slope. An intermediate slope is ??? say 15 degrees. I'd say that the increase in slope more than overcomes the increased friction on the skis (on a hard packed run).

Furthermore since aerodynamic drag is a function of the velocity squared, as your speed increases the relative drag from the friction of the skis becomes small compared to the aerodynamic drag (on a hard packed run).

The velocity squared term is also why it takes some effort (tuck, speed suit, steeper run etc) to reduce your drag coeficient to get over 40mph.

I have to make the distinction of hard packed because out here in Utah we often have to find a 30 degree slope just to get moving to overcome the drag from 20+ inches of new snow :]

What price freedom
dirt is my rug
well I sleep like a baby
with the snakes and the bugs
post #38 of 67
quote: "Though I'm not Gonzo, I'll state the obvious: skis are sliding (dragging) and bikes are rolling. There is umpteen times the drag on skis than on the ball bearings of a bike."

you obviously haven't been skiing on any slabs of ice lately. My mountain is one big slab - hence the reason I don't bother with wax.
post #39 of 67
I know I've hit about 70 at one point, and done a run at an average of 60mph, but it's a different world at over 50mph. I doubt that more than a very few recreational skiers hit more than 30, ever. In a nastar course, I can't imagine people going more than about 20, certainly not 40-50. WC GS racers don't hit those speeds in competition, and rarely in Super G (one or two points during a race).

Here's a more realistic experiment, based on Ott's recommendation. Drive down a road at whatever speed, and just hold your pole out the window. Check the wind resistance. At 50-60 mph, it becomes very difficult to even get the pole tip facing straight down. When was the last time you were skiing and couldn't get your pole tip in front of you? Admittedly, when I was living out west, I experienced that a lot, but I was 155lbs on 210cm SuperG boards, and hauling arse at Keystone every night with noone else on the hill.

I find the experience of speed between a bike and skis, exactly opposite of J Shefftz's experience. But then, I'm not a racer. For the first time, last week, I went riding and had a speedo avaialble (Gill has one on his road bike). I was suprised how easily 25mph came on a paved surface. I would have guessed I was doing about 15-18. At 25mph on skis, you feel like you are going fast, not scary fast, but fast. On a bike, it doesn't feel very fast. Mountain biking would be a bit different, though.
post #40 of 67
WC men will often go over 80 mph in DH, and on the flat at Kitzbuhel they've almost hit 100 mph (I know one year they thought it would happen, but speeds topped out at about 95).
I still think that feeling a pressing sensation from the wind all over your body is the best indication that you're going pretty fast. If you don't get that sensation when you stand up then you can't be going over 40.
Supposedly even with bindings set at 22+ speed skiers would be ripped out of their bindings from the force of the wind if they were to stand up mid-run.
post #41 of 67
looks like i will have to rig something to hold a gps unit on my helmet. The results of the study will be posted sometime in December.

check your math.
post #42 of 67

thanks jocanadian I cut and pasted without checking the math at all. that's what I get for trusting someone else to do the math.
80MPH=128.648 KPH
post #43 of 67
As far as ski vs. bike speed, skis (properly tuned and waxed) will be faster than a bike. The plastic used on ski bases has an incredibly low coefficient of friction. The ski based actually melts the snow, so you are always skiing on a thin layer of water (lubricant). The ball bearings in a bikes wheel have a low coefficient of friction, but the rubber bike tire has a much higher coefficent of friction than a ski base sliding over the snow. Want proof: How many bike riders have hit 154mph like speed skiers do?

The police speed gun in question was a certified unit, so I don't doubt the results.

One clairification: The fastest racers in the course were not the general public. The were masters racers (most were ex-college racers) using the course for timed training runs. Also our mountain's NASTAR course tends to be steeper and longer than most.

Pole Plants: In a high speed carving situation, traditional pole plants are not neccessary, and as some have pointed out, almost impossible to do at speeds over 30mph. How many GS or SuperG racers have you seen do traditional pole plants lately?

Gonzostrike: Obviously you don't have a backround in science or engineering, for your knowledge of Skiing Physics is pitiful. Why don't you go back to school and learn some facts before making your childish statements.
post #44 of 67
TJ, I think the rolling resistance is a lot lower than the friction created by hundreds of square inches of surface contact that skis make. Wheels with bearings have almost no surface friction, whereas skis have tremendous amounts. If you put a skier on good hard smooth snow, and a biker on pavement, both at a 15 degree pitch, I would bet that the bike accelerates faster and maintains a higher speed, assuming aerodynamics are similar between the two.

I could be wrong.

Maybe PhysicsMan can settle this with facts? Come on PM, break out the slide rule!
post #45 of 67
speed skiing has been called the fastest non-motorized sport on earth.
speed skiers go faster than the same people on the same slopes with the same outfits on bikes.
my physics is rusty but the numbers of both record holders dont lie.
post #46 of 67
I would think the aerodynamics have more to do with the top speed than the friction on the snow. I would venture a guess that if you could get a sled to not bounce around and put it on skis and let it go on the same course as the skier it would go a lot faster than the skier.
On a bicycle you have a lot more surface area in the wind and without the advantage of wind tunnel tested suits, helmets, leg spoilers, farings and other products the skier has the advantage.

I can't remember the formula (Physics man?) but I seem to remember that the wind resistance goes up exponentially with speed depending on surface area.
post #47 of 67
Someone else posted this here before. Interesting web page. Usual Disclaimers apply...
dchan is taking us down the right path, you've got friction and wind drag to deal with. Wind drag is proportional to the object's area and its velocity squared.

spending WAAAAY too much time on this.


-DS-<FONT size="1">
<FONT size="1">

<FONT size="1">

[This message has been edited by dirtsqueezer (edited August 28, 2001).]</FONT>
post #48 of 67
back to the original spirit of the thread.
The 30+ I might hit is more than enough for me. It hurts enough when I fall going my mortal 20+MPH
post #49 of 67
> John H.: Maybe PhysicsMan can settle this
> with facts? Come on PM, break out the
> slide rule!

> dchan: I can't remember the formula
> (Physics man?) but I seem to remember that
> the wind resistance goes up exponentially
> with speed depending on surface area.

Hey Guys - In the past week or two, I've been busy and not as active on the skiing forums as I would like to have been.

Anyway, I looked over the previous posts in this thread, and if I think the question is essentially whether a bicyclist going down the same grade as a skier would go faster or slower.

Its kind of a vague question because to make it specific you got to specify all sorts of things that you can't really specify but what the heck - here goes.

First, I'm going to assume that the bicyclist is on a nice paved, smooth surface of whatever grade is necessary for the test. I realize that it might be a tad difficult to locate a nice smooth road with a 35 degree slope (and get somebody on a bicycle to go down it and reach terminal velocity).

There are two classes of forces which impact both the hypothetical skier and cyclist: aerodynamic drag and "everything else".

Aerodynamic drag is proportional to Cd (drag corfficient) TIMES the velocity squared. The coefficient of drag depends fairly weakly on velocity and a bunch of other things.

The "everything else" category includes rolling resistance, bearing friction, Coulombic snow friction, (snow) plowing and compaction drag, etc. The net effect of all of these forces can be approximated by a constant plus a second constant times velocity (to the first power, not squared). As usual, see, "The Physics of Skiing" for a more complete discussion of these forces.

On really low angle slopes, you never are going all that fast (on either a bicycle or skis), so you can neglect aerodynamic drag for both the biker and the skier. Since the various non-aero drag forces acting on the bicycle are less than those acting on a ski, the bicyclist would clearly win. In fact, if its a low enough angle hill, the skier might not even be able to overcome static friction and hence might never even get going - grin.

OTOH, consider what happens when you are going fast on really steep slopes. Since the worst of the non-aero drag forces increases only linearly with velocity, whereas the aero forces increase as the square of the velocity, the aero drag forces will always dominate the non-aero drag forces, and the answer pretty much comes down to the single issue of which is larger, the Cd for skier or the Cd for the bicyclist.

My guess is that unless you are allowing something like a low recumbant bicycle with full aero fairings, the skier will almost certainly win. The Cd of normal cyclists is almost certainly much larger than the Cd of a skier in a full tuck.

Just my $0.02,

Tom / PM
post #50 of 67
For thoes in the associations, I just got a mailer from sportstarprosales they have a Bushnell speedster for sale, it will clock most anything, even skiers. has a msrp of $304 tho.
post #51 of 67
I thought I saw that for $189.
post #52 of 67
I wasn't going to say what the price in the mag was, might piss off anyone looking for it. msrp of $304
post #53 of 67
As an alternative to GPS for speed measurement, I carry a handheld combo thermometer/anemometer that was designed for sailing (a Kestrel 2000). It registers instant,average, and maximum temp, and wind speed (plus windchill). Just have to remember to compensate for the wind.
I've clocked myself at 57 MPH airspeed and yes, anything over 30 feels fast. Over 45 seems to be when things start to get aerodynamicly interesting. I just hold it in one hand while tucking those rare empty steep runs after a few warmups.
post #54 of 67
How effective are GPS recievers for measuring speed on a ski hill? Don't you need a 3 satellite "fix" for accuracy, which is not always available in mountainous terrain? And wouldn't the slope also affect the reading, as it is measuring your speed across the circumferance of the Earth and not your actual ground speed?
post #55 of 67

Prior to attacking anyone else on their lack of knowledge on the "physics" of skiing, please do a bit of research.

That thin film of water..... it is not caused by the materials in the ski base. It is simply caused by the weight of the person placing the materials (snow) under compression.

That thin film of water does NOT act as a lubricant. Conversly, it acts to slow the skiier much the same way a flat pane of glass would be difficult to move on a flat surface ("suction") when wet. Racers spend time in order to "structure" the base of the ski. Basically, they rough up the base with a brush in order to break that flat smooth surface of a freshly waxed ski.

BA not an MS
post #56 of 67
If you wanted to take it one step further, you are on skis, on an oil slick (yep fluro or hydrocarbons), on water, on snow.

The sliding ability of the ski come from a combination of base structure and the oil water interface. Friction between the ski and the snow causes the water layer not just the weight of the person on the ski. If the ski wasn't moving I don't think it would form.

The colder the temps the less important wax and structure become. The skis don't generate enough friction to form the water layer. From 10 below on down things don't change much.
post #57 of 67
Yuki: That layer of water that is formed by the ski certainly does act like a lubricant! As a ski passes over the snow, the friction generated transforms the relatively abrasive snow crystals into a liquid state. The film of water, along with the chemical make up of the plastic base material and wax, allows the ski to achieve a very low coefficient of friction (approaching 0 at 32-33 degrees F). As Grizz stated, the effect decreases with decreasing temperature. All ski bases are structured to prevent the suction you described. As far as researching this subject, I have undergrad degrees in both Chemistry and Physics and a M.S. in Chemistry. I spent 4 years racing in college, and currently Masters race, so I guess I know a little about ski base prep too.
post #58 of 67
Just to show that going very fast on a bicycle (mountain bike with slick tyres, and me with 4 years racing experience) is certainly possible i have been 94km/h (94 kilometers/hour = 58.40878 miles/hour) and i was in control and never had doubts about that. Whether this helps to prove anything on what you guys are talking about i dont know but i thought i'd say that anyway. I believe the speed recodring was very accurate as i was using a $180 cycle computer which i have also compared to car speedos in the past.
Cheerio, Tim.
post #59 of 67

"and they call him the Streak"
Ray Stevens
post #60 of 67
The Angular momentum (of the rotating wheel) will only slow your acceleration. It has no effect on your terminal velocity.

Angular momentum stores energy in the system, unlike drag, friction etc which dissipate energy. IE the same angular momentum which slowed your acceleration will slow your deceleration.

What price freedom
dirt is my rug
well I sleep like a baby
with the snakes and the bugs
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