What makes skis faster? ...Narrowness or Length?

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What makes skis faster? ...Narrowness or Length?

Postby JeffOYB » Mon Jan 09, 2017 12:53 pm

...And why?

It does seem like skis get faster as they get longer. ...Is this due to lower pressure?

It also seems like they get faster as they get narrower. ...Is this due to increased pressure?

Whew.
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Re: What makes skis faster? ...Narrowness or Length?

Postby JeffOYB » Thu Jan 26, 2017 2:37 pm

bump...

what affects ski speed more: length or width?
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Re: What makes skis faster? ...Narrowness or Length?

Postby MN Hoser » Thu Jan 26, 2017 3:06 pm

My feeling has been that a longer ski ends up being a more universal ski. So it can handle more snow types. No clue about width, but that would make more difference as the snow becomes softer.

I have also come to the conclusion, that when you heat up petex and let it cool (like when you make a ski), it's really hard to predict the shape that the petex will take. So it's hard to predict the final pressure distribution of the ski. I am always surprised at the results I get when I wax three or five pairs the same and go ski them. (I tend to do this in extreme conditions, but also the week before the Birkie if it looks like the temps will be the same a week later). There can be some major differences and some pairs feel exactly the same. It doesn't seem to depend on structure at all.

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Re: What makes skis faster? ...Narrowness or Length?

Postby dcpattie » Fri Jan 27, 2017 5:42 am

If they're anything like a bicycle tire then the results may surprise you. For years the conventional wisdom on bike tires was the narrower (and harder) the faster. Now everyone is racing on wide tires (23-24mm vs 19-20mm).

For races where folks are mostly DPing - I'd think whatever platform provides: (1) stable platform to transfer power and (2) the most "run" on the snow.
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Re: What makes skis faster? ...Narrowness or Length?

Postby Magnus Johansson » Fri Jan 27, 2017 6:48 am

dcpattie wrote:If they're anything like a bicycle tire then the results may surprise you. For years the conventional wisdom on bike tires was the narrower (and harder) the faster. Now everyone is racing on wide tires (23-24mm vs 19-20mm).

Interesting. Thanks, Dave.

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Re: What makes skis faster? ...Narrowness or Length?

Postby MN Hoser » Thu Feb 02, 2017 5:51 pm

The reason wider tires are being used in cycling is the larger air volume (more shock absorption on rough roads). You can also run lower tire pressure without pinch flatting.

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Re: What makes skis faster? ...Narrowness or Length?

Postby JeffOYB » Fri Feb 03, 2017 7:15 am

it used to be thought by bike racers, some of whom used science, that narrow hard tires were faster.

so what makes fastest skis?

sometimes it seems like length helps -- more surface area?

but width seems to hurt -- but what does width do besides add more surface area?

pressure seems to be key, flex -- but what about a longer ski for a given "proper" pressure curve? do we know the ideal pressure curve?

is there published research about this? seems like ideal dissertation bait...
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Re: What makes skis faster? ...Narrowness or Length?

Postby skiffrace » Fri Feb 03, 2017 10:26 am

We say that skis "glide", but in reality they usually waterplane on a thin film of water.
Water melts above 0 Celsius at normal atmospheric pressure, but the higher the pressure, the lower the melting temperature.
The weight of the skier creates the extra pressure so the snow pressed by ski melts when the air/snow temperature are below 0 Celsius.
When the air/snow temperatures are very low, the skis glide poorly because the pressure is not enough to create the microfilm of water, and the friction of the ski on snow is higher.

Are narrower skis faster? The "fastest" width may depend on factors such as the air and snow temperature, and the weight of the skier. For the same length, narrower skis may be faster on a very packed and very cold snow because a higher pressure is required to create the microfilm of water.
Think of ice as "super packed snow" - a condition where short and very thin skates (very high pressure) are needed to create the microfilm to glide on.
On softer and warmer snow, a wider ski may provide best speed, because the higher temps will allow the microfilm to form even at lower pressure, while narrow skis might "sink" into the soft snow too much.

Since skis are made only in few widths, they cannot be precisely customized based on conditions, and a reasonable versatile width is used.
Finally, it's not the speed of the ski that matters, but the speed of the ski+skier system.
What might be the fastest ski moved by a static weight in a straight line will not be the fastest ski moved by human power on a complex course.

PS. don't bet the farm on the above hypothesis, it's just my educated guess.


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