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A flawed experiment v=f(Long and short skis)

post #1 of 20
Thread Starter 
I went skiing today.

I had a late night last night and only had time to wax one pair of skis. I chose to wax my SCs (165 cm 13-m radius). I still brought my old SGs (208 cm about 60 to 70: m turn radius) along with my GPS, just to try and see once again if longer skis go faster. Of course I realized after the first run when my max speed was only 93 kph that I had to get them waxed, so I dropped them off at the shop and skied the SCs. The SCs got up to 97 kph today. Later with freshly waxed SGs, try as hard as I might, I could not beat that 97 kph. Did I have better wax at home than they used in the shop? It does look like I did a better job scraping and brushing BTW.

When I got home I looked at the track logs. In fact it was a tie. Several runs maxed out at 60 mph (Lets ignore the one point that said 64). It seems that aerodynamics is so important even on a mild slope that it overpowers the other variables.

I will have to try this again on a bigger hill some day when I get out west.
post #2 of 20
Good Report,
I am also one who enjoys getting out the long boards. People may look at you funny, but I have found over and over, when you let them run, they tend to be a smother ride w/ no wobble.

Dont let the long boards die!!!!
post #3 of 20
When you get up into the range of 60 mph drag increases with speed cubed so yes aerodynamics is HUGELY important.
post #4 of 20
great experiment could you post your data?
post #5 of 20
Two better tests would involve tracking the acceleration to speed from the start and timing the whole run(assuming all other things are equal.) You would find the better wax will get you up to speed a lot faster than the cheaper wax. Once you start reaching the speeds you are claiming, aerodynamic drag will dominate. I wouldnt use max speed as an indication of anything other than how well you are dealing with the drag on the particular run you are timing. Trying to use max speed on a run as a means of comparing wax is a lesson in futility - there are too many other variables involved. The goal of racing is not to decide who reached the highest speed, it's who got down the run the fastest. The questions you should be asking are how fast did you get down the entire run and how quickly did you get up to speed from a full stop?
post #6 of 20
Sorry, but I refuse to believe that Ghost can reach 60mph on 165cm SCs. This reminds me of another thread where a rather poor skier claimed to have reached over 63 mph. Sadly he looked like this.
post #7 of 20
I guess it is possible to hit 60mph on 165 SC's if the run was perfectly groomed,very hard, and you straight-lined it. Personally, I wouldn't try it unless I knew I had a really good health insurance policy.

Outside of speed skiers, I don't any competition where the competitors appraoch the gate saying to themselves, "my goal is to reach X miles per hour." The goal is to get through the course with the best time. The resulting time involves much more than the max speed reached.
post #8 of 20
Thread Starter 
My goal in the experiment was to investigate the myth that long skis go faster, like an episode from the show "Mythbusters". I was not looking at racing applications.

It seems that they may influence the skier to feel more comfortable and choose to ski faster, but if you try to go as fast as you can, you still reach the same aerodynamically and slope limited top speed.
post #9 of 20
Quote:
Originally Posted by Ghost View Post
My goal in the experiment was to investigate the myth that long skis go faster, like an episode from the show "Mythbusters". I was not looking at racing applications.

It seems that they may influence the skier to feel more comfortable and choose to ski faster, but if you try to go as fast as you can, you still reach the same aerodynamically and slope limited top speed.
'Long skis goes faster' may or may not be true, depending on how the ski is being used. In a straight run, a longer ski will actually go slower than a short ski due to the fact that there is more surface area in contact with the snow to offer more friction and resistance.

The statement that 'Long skis are faster' really means: when riding the sidecut as opposed to skidding, long skis spend more time in the fallline due to their longer turn radius and therefore average a higher speed down a slope. Likewise, when riding the sidecut, short skis spend more time cutting accross the fallline due to their shorter turn radius and will have the lower average speed down the slope.

If someone is skidding their turns, the above is a moot point and the longer ski will probably be slower simply because more surface area offers more resistance when skidding and bleeds off more speed.
post #10 of 20
Quote:
Originally Posted by TomB View Post
Sorry, but I refuse to believe that Ghost can reach 60mph on 165cm SCs. This reminds me of another thread where a rather poor skier claimed to have reached over 63 mph. Sadly he looked like this.
I don't. Not at all. It wouldn't surprise me a bit.
post #11 of 20
Where we ski in Ontario one would have to tuck and straightline like crazy to reach 60 mph. Is anyone crazy enough to straightline 13m radius skis at 60 mph. Common guys!

Ghost's conclusion that "if you try to go as fast as you can, you still reach the same aerodynamically and slope limited top speed." is a joke. Perhaps we can also reach 60 mph on skiboards based on this conclusion?
post #12 of 20
In another thread where we were debating top speeds and doing some analysis, it was determined that aerodynamic drag is indeed the biggest factor. The ski-snow friction effect is much smaller in comparison, assuming you're not on velcro skis. You can almost neglect the friction effect in most cases.

Re: long skis versus short skis and the friction effect -- in reality, there is probably an optimum to be calculated between friction and surface loading. But since the friction effect is so small, it doesn't matter much.

SureValla, drag is proportional to velocity squared, not cubed.
post #13 of 20
++ what skier 219 says. You probably won't notice much of a difference in speeds of different ski legnths with all other things equal using a GPS. That would only buy you a second or two on a GS course. Shorter skis do definately get you through the slalom gates quicker of course due to the manuverability factor.
post #14 of 20
Quote:
Originally Posted by TomB View Post
Is anyone crazy enough to straightline 13m radius skis at 60 mph. Common guys!
Is your complaint that it is not possible to go that speed or that you believe only crazy people would do it?
post #15 of 20
Thread Starter 
Quote:
Originally Posted by TomB View Post
Sorry, but I refuse to believe that Ghost can reach 60mph on 165cm SCs. This reminds me of another thread where a rather poor skier claimed to have reached over 63 mph. Sadly he looked like this.
Sorry Tom, you have this thread confused with another thread where we were debating how fast you could ski. By all means carry the argument over to that thread. This thread is about if you can go faster on 208s than on 165s (on an easy hard snow groomer). I used to think so. Now I don't think it matters all that much if at all.
http://forums.epicski.com/showthread...ght=gps&page=9
post #16 of 20
My expectation would be that it's more comfortable to go 60mph on the GS or DH skis than the SG skis. But I feel like air resistance gets important around 20mph and turns into a huge factor by 40, so I'm with the people saying that it shouldn't have a lot of effect on a skier's ability to do 60.
post #17 of 20
Harry Morgan: Is your complaint that it is not possible to go that speed or that you believe only crazy people would do it?

I simply question Ghost's claim that he can hit 60 mph on 13m radius skis. Where he skis he would have to straightline it. I don't believe many people could keep such short shaped skis flat in a straightline at that speed.
post #18 of 20
Also the claim that long skis "are" (not "go") faster comes from a racing context: in that case its true in the sense that a long ski can hold a line and stay carving while going much faster than a short ski. If you tried to run a downhill on a slalom ski it would try to turn too hard, and you'd lose your edge and start slipping (or crash into the netting).
post #19 of 20
Thread Starter 
Quote:
Originally Posted by TomB View Post
Harry Morgan: Is your complaint that it is not possible to go that speed or that you believe only crazy people would do it?

I simply question Ghost's claim that he can hit 60 mph on 13m radius skis. Where he skis he would have to straightline it. I don't believe many people could keep such short shaped skis flat in a straightline at that speed.
It is difficult to be sure. Up to a certain point you can alternate between edges in a sort of carved wheedle, but faster than that you just have to go with it. Probably not many people could, maybe only about 3 percent.

I totally agree that the longer skis will do a better job of holding a line at speed.
post #20 of 20
Quote:
Originally Posted by MojoMan View Post
In a straight run, a longer ski will actually go slower than a short ski due to the fact that there is more surface area in contact with the snow to offer more friction and resistance.
Well I think that depends on several factors but mainly snow temperature. Friction between our skis and the snow has 3 components, dry friction, meltwater lubrication and capillary drag.

Dry friction is not dependent on surface area because a change in surface area implies a change in the normal force per unit area acting on the surface. The total resistance therefore does not change.

At warmer temperatures where we get a thick layer of water over the snow, viscous friction will be dominant and that should be dependent on surface area.
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