Grip physics?

Hi All,

I have been thinking about grip, and kick and how my technique and size
play into my performance in low-grip conditions.

I am heavy (100kg, 225lbs) and do not have great technique (yet!). My
skis are on the stiff, cold side. In good cold conditions I have great
grip, the skis feel nailed down and I can get all my power to the
ground, even on steep inclines.

In low-grip icy conditions it is a different story. I know softer skis
would help, and most of all better technique, but I wonder what my
weight means on steep slippery inclines. I can't get any power down. It
seems like I have it worse than others I've seen. Is my weight a
factor, or is it just the other variables?

Traction is a function of how much down-force is available (from weight
and rythmn), but what are the limiting factors? To get my weight up a
steep incline as fast as my fitness allows I need to get more power to
the ground in slippery conditions. Does my need for power due to weight
go up faster than my weight's ability generate friction as the incline
get steeper?

Thanks!

Joseph

I can't answer this on-topic, but I wonder, with which technique are you
getting into trouble?

I know that in MTB, with a heavish and super-tall body, I DO can get the
traction I need, from the same tires as racer types. My weight indeed seems
to add the required friction. I also have sufficient grip in corner, even
though more weight is further away from the ground.
The way I put my power down on tires makes all the difference on steep
climbs, I need to be smooth, non-agressive, or I'll slip, same with short
people. I've learned his over the years, and can now use it in my advantage
even in the most slippery conditions.
I wonder how ski length affects all this. Do longer ones provide more
directional (classic) and sideways (skating) grip on snow? It does work that
way with tires, wider ones, or those with a larger radius, grip better and
more predictably.

schreef in bericht
oups.com...
Hi All,

I have been thinking about grip, and kick and how my technique and size
play into my performance in low-grip conditions.

I am heavy (100kg, 225lbs) and do not have great technique (yet!). My
skis are on the stiff, cold side. In good cold conditions I have great
grip, the skis feel nailed down and I can get all my power to the
ground, even on steep inclines.

In low-grip icy conditions it is a different story. I know softer skis
would help, and most of all better technique, but I wonder what my
weight means on steep slippery inclines. I can't get any power down. It
seems like I have it worse than others I've seen. Is my weight a
factor, or is it just the other variables?

Traction is a function of how much down-force is available (from weight
and rythmn), but what are the limiting factors? To get my weight up a
steep incline as fast as my fitness allows I need to get more power to
the ground in slippery conditions. Does my need for power due to weight
go up faster than my weight's ability generate friction as the incline
get steeper?

Thanks!

Joseph

Jan Gerrit Klok wrote:
I can't answer this on-topic, but I wonder, with which technique are you
getting into trouble?

Diagonal stride in icy-tracks. I feel like I can only push with a
fraction of my available energy. This is of course the same for
everyone, but I suspect weight makes this a problem on climbs before it
is a problem for lighter people.


I know that in MTB, with a heavish and super-tall body, I DO can get the
traction I need, from the same tires as racer types. My weight indeed seems
to add the required friction. I also have sufficient grip in corner, even
though more weight is further away from the ground.
The way I put my power down on tires makes all the difference on steep
climbs, I need to be smooth, non-agressive, or I'll slip, same with short
people. I've learned his over the years, and can now use it in my advantage
even in the most slippery conditions.

On steep climbs, it was usually wheelies that were my problem, not
grip. Now I have a 2-wheel drive bike so I can stand up on really steep
climbs and move the center of gravity forward to even the load. So no
wheelies, and no slipping.

I wonder how ski length affects all this. Do longer ones provide more
directional (classic) and sideways (skating) grip on snow? It does work that
way with tires, wider ones, or those with a larger radius, grip better and
more predictably.

The grip-zone on my classic skis isn't that much bigger area-wise than
my wife's skis, though I weigh at least 40kg more than she does.

As for tires on cars, whenever I see a car that is having problems
getting up a icy hill, it is usually a larger car, a truck, or heavily
loaded small car. I used to have a BMW 318 and a 520. Both with the
same size winter tires. The 520 weighed about 400kg more. It didn't
slip as much when I gassed in in the turns despite more power, but it
also had more difficulty starting on icy surfaces and getting up hills.
Ice is funny stuff.

Joseph

schreef in bericht
oups.com...
Hi All,

I have been thinking about grip, and kick and how my technique and size
play into my performance in low-grip conditions.

I am heavy (100kg, 225lbs) and do not have great technique (yet!). My
skis are on the stiff, cold side. In good cold conditions I have great
grip, the skis feel nailed down and I can get all my power to the
ground, even on steep inclines.

In low-grip icy conditions it is a different story. I know softer skis
would help, and most of all better technique, but I wonder what my
weight means on steep slippery inclines. I can't get any power down. It
seems like I have it worse than others I've seen. Is my weight a
factor, or is it just the other variables?

Traction is a function of how much down-force is available (from weight
and rythmn), but what are the limiting factors? To get my weight up a
steep incline as fast as my fitness allows I need to get more power to
the ground in slippery conditions. Does my need for power due to weight
go up faster than my weight's ability generate friction as the incline
get steeper?

Thanks!

Joseph

On steep climbs, it was usually wheelies that were my problem, not
grip. Now I have a 2-wheel drive bike so I can stand up on really steep
climbs and move the center of gravity forward to even the load. So no
wheelies, and no slipping.
For some reason bike manufacturers give everyone from 1m30 to 2m30 the exact
same chainstay (horizontal rear fork) length. So, taller riders tip back
over more easily. Bike manufacturers care more about cheap production and
large easy sales than designing stuff that actually works well for the rider
that's buying it. I suppose if a ski maker put the same length grip area on
both kids' and your ski's, a very similar situation. I am a passionate
believer that everything in sports goods should be proportionate to the
athlete's body.
I won't get too much into bikes here, I have another place for those rants
of mine (www.mtbr.com , I post as Cloxxki).

I wonder how that works out with ski width. Does that stay the same for 30kg
kids and 100kg men? would we biggies suffer if ski's were made wide, and if
so, why?
To my newbie popular-science-fan eye, not affected by 100 years of ski
evolution, it seems like Joseph would like ski's to match his leg length,
with a width to match his weight. If someone knows links to any studies on
that subject, I'd appreaciate those a lot.

Jan Gerrit Klok wrote:
On steep climbs, it was usually wheelies that were my problem, not
grip. Now I have a 2-wheel drive bike so I can stand up on really steep
climbs and move the center of gravity forward to even the load. So no
wheelies, and no slipping.
For some reason bike manufacturers give everyone from 1m30 to 2m30 the exact
same chainstay (horizontal rear fork) length. So, taller riders tip back
over more easily. Bike manufacturers care more about cheap production and
large easy sales than designing stuff that actually works well for the rider
that's buying it. I suppose if a ski maker put the same length grip area on
both kids' and your ski's, a very similar situation. I am a passionate
believer that everything in sports goods should be proportionate to the
athlete's body.
I won't get too much into bikes here, I have another place for those rants
of mine (www.mtbr.com , I post as Cloxxki).

I'm a big fan of proportionality too. That's why I use 195mm cranks on
my bike!

I wonder how that works out with ski width. Does that stay the same for 30kg
kids and 100kg men? would we biggies suffer if ski's were made wide, and if
so, why?

I think the issue is surface area to skier weight, and certain ratios
for certain usage. Ie racing skis go on packed trails so they don't
need as much float, while back-country need lots of float. And then the
area is limited by practical issues like track width, and controllable
length, and predictable flex.

I use 210cm classic, and 195cm skate. I would have no problems using
even longer classic, but the 195 skate gets crowded on narrow climbs.
It may be that way for everyone, I don't know, but with a 96cm inseam,
and 195cm skis going 90deg to each other, that gets pretty wide.

To my newbie popular-science-fan eye, not affected by 100 years of ski
evolution, it seems like Joseph would like ski's to match his leg length,
with a width to match his weight. If someone knows links to any studies on
that subject, I'd appreaciate those a lot.

I suppose narrow glides better, otherwise why would racing skis be
narrow? Give me length!

Joseph

I'm a big fan of proportionality too. That's why I use 195mm cranks on
my bike!
I envy you, longest I have is 185mm, and I've got a 99.5cm inseam!

I suppose narrow glides better, otherwise why would racing skis be
narrow? Give me length!
Too narrow and it would appoximate speedskating ski's (knifes), that would
go no-where. There must be an optimum somewhere, but I can't believe it's
40-45mm for every skiier of any height or weight.

More speculation....how about strength to wt ratio. It feels to me that
arm strength is a big factor in classic, and if you're more of a
clydesdale, your ratio may be low.

I have a hard time getting grip with my Cold classic skis in difficult
conditions. I have a much easier time with my Plus and Wet base skis.
(My colds have a longer pocket, and my Plus and wet have short pockets,
if that help with a mental picture.) So there's definitely a ski effect
also. I think there may be something to how easily the ski compresses
past flat, so when the track is a bit uneven, you can still get the wax
down.

Jay Wenner

In the (simple) version of the physics theory of static friction, the
difference in the weights of two skiers should not make any difference for
grip versus leg-push: If they're using proportionally similar skis and wax
and technique to climb up a hill of the same steepness grade and same snow
quality.

I like Jay's idea that arm-strength might tend to be disproportional, for
heavier skiers. Presumably leg-strength is roughly proportional from the
need carry and more body-weight in general living and off-snow exercise
activities. But not many land-based aerobic activities put as much emphasis
on arms as Classic cross-country skiing.

Since the topic is "physics", I mention that there's lots of detailed ideas
about the physics of grip (also Classic glide and pushing and Classic
hill-climbing) linked from this page:
http://roberts-1.com/xcski/classic/secrets

Ken

Ken Roberts wrote:
In the (simple) version of the physics theory of static friction, the
difference in the weights of two skiers should not make any difference for
grip versus leg-push: If they're using proportionally similar skis and wax
and technique to climb up a hill of the same steepness grade and same snow
quality.

So in other words, a heavier skier up a given climb will need to
transmit more force to maintain a given speed, but the friction
afforded by the skier's weight goes up proportionaly to this need for
greater force transmission. Right?

Is the friction related to the weight per area of contact, or just the
area? Is the only thing that needs to be proportional the grip-zone
area to skier weight ratio, or does that not matter and just more area
is better no matter what?

I like Jay's idea that arm-strength might tend to be disproportional, for
heavier skiers. Presumably leg-strength is roughly proportional from the
need carry and more body-weight in general living and off-snow exercise
activities. But not many land-based aerobic activities put as much emphasis
on arms as Classic cross-country skiing.

Disproportional in what way? That heavy skiers have weaker or stonger
arms? I wouldn't be surpised if the tendency went either way. But I
suspect that it is so individual that it is hard to think about in in
general terms. No doubt that people in general get more oppurtunity to
exercise their legs than arms, but heavier people probably have more
muscle mass, that even untrained would be stonger than an untrained
person with less mass.

Since the topic is "physics", I mention that there's lots of detailed ideas
about the physics of grip (also Classic glide and pushing and Classic
hill-climbing) linked from this page:
http://roberts-1.com/xcski/classic/secrets

I'll check it out!

Joseph

Disproportional in what way? That heavy skiers have weaker or stonger
arms? I wouldn't be surpised if the tendency went either way. But I
suspect that it is so individual that it is hard to think about in in
general terms. No doubt that people in general get more oppurtunity to
exercise their legs than arms, but heavier people probably have more
muscle mass, that even untrained would be stonger than an untrained
person with less mass.
Not being disrespectful at all, but for a "heavier" person, the change of
the arms being relatively weak seems greater than the opposite. If the big
guy has some friendly soft spots, already the skinny lightweight with the
matchstick arms will end up stronger.
Even a body builder with phenomenal arm strength, would still just have a
similar strength/weight ration as the match stick, due to weighing twice as
much. Perhaps more explosive yes, but worth less in a 15km race I'm sure.

I'd be interested to know why XC Ski's are so narrow, and how that would
relate to weight.
It seems a really flexible narrow ski under a heavy and strong skier would
approximate a pole tip more closely, thus maximum grip. But does it really
work that way in practice, or is he better off with a longer-than-standard
grip zone, perhaps even wider?