Grip physics?

Learning to read on ability vs. flex, thanks! Getting closer already.

Alright, so assuming the exact right flex for his abilities and weight,
right lengths, etc.
2 sets of ski's, one as sold everywhere, one customized to be significantly
(20%?) wider, that still fits between tracks. How will grip and glide be
affected?

For glide we'll all agree that a 1cm narrow ski for someone ~60-100kg would
be like a knife cutting deep, so very slow gliding. Perhaps great grip,
though you'd destroy the trails all by yourself and possibly lose energy
pulling skis out of the snow after kicking off.

But now let's take a wider-than-regularly-available ski, but still the same
ballpark. The aforementioned +20%. Slow or fast, grippy or slippy?
Weight-to-surface Joseph is getting a much different figure (+66%) than the
60kg skier of similar height and ability now, as ski's seem to end up around
the same width. What if his weight-to-surface came down a bit?

Taking it to the extreme, a hypothetical skier, twice the regular height of
a human, 12 feet tall, 600kg. Even with proportionate width ski's (~9cms?),
his weight-to-surface is greater than with typical humans. This is because a
man twice as tall weighs eight times as much (if I'm getting this right),
but only gets twice the ski length for practical reasons. Even with 9cm wide
skis, weight-to-surface for our giant is twice that of the 6 feet tall
skier. I would wager the giant has a hard time gliding, at least on the
flat. Grip, well he might rip up the trails with his skinny skis. Snow
density doesn't work out for him, something like that.
Why not give our giant even wider skis? They won't get in the way for him,
and weight might not even end up significantly higher, as they could also be
made thinner. The trails will thank him, and my gut says it would glide
faster.
Now with a 12-foot dinosaur extreme measures seem required to get a good ski
fit, but our friendly friend Joseph might already enjoy slightly wider skis
that still fit in the trails, while crushing the snow a bit more similarly
to his 60kg buddy of identical height and technical ability.

As you'll notice, I have a deeply rooted love/hate thing for proportions,
probably due to being built XL myself. I'd love to learn and understand how
the physics works in case of a skier's weight and his ski's width, for glide
and grip, as in other sports and business, the rules of proportion as I
understand them, always apply for best performance.

I did Google the topic, but the only places where weight to width ratio
seems to come up regularly, is mountaineering and alpine, where obviously
snow is less dence.
A Bianthlon rulebook I came across stated a minimum width of 40mm under the
boot, but that doesn't mean narrower is better, does it?

Zach wrote :
As for a the possibilities of better grip from a wider ski - I would
suggest that the overwhelming factor determining grip is the amount of
dowforce the skier can apply through the wax.
Do you mean downforce per surface unit, or after deducting flex from his
boot-on-ski pressure?

And:
I don't think that a wider ski would help
grip in the least - at least not before it completely killed the
handling characteristics and running speed of the ski.
Specifically, also not for a guy with more weight for his ski length?
Does a narrower ski automatically equal faster, for skiers of any weight, or
any surface?
would theorical inch-wide skis make the best classic skiers even faster?

Thanks,

J

"rw" schreef in bericht
oups.com...
J
A skier of 60kg should never ski on a ski which is closed at 100kg and
visa versa.
The skier of 60kg: And here is the kicker::::::: if is a super athlete
and a excellent classic skier.( see now we have to factor in the
persons skiing ability!!!!!) Should buy a ski that closes at 100% of
his body weight. A skier like Joseph who admitted he is not an expert
in classic technique. Should buy a ski that closes at 50kg or even
less. So when Joseph climbs or when he gets tiered he will still be
able to close the ski and have excellent grip.

Now to answer your question (Which is not real world)
For Joseph of course at 100kg he will be faster on the downhills then
any body else because he has more weight behind him.
Yes he could get a wider ski and have more surface for glide and grip
with the same length ski.
The wisdom is more base more glide more grip. Now this is if the skis
have excactly the flex for him. (His WEIGHT his SKIING ABILITY = SKI
FLEX 100kg - 25%= 75kg for a intermediate skier)
I hope this was helpful

rw

Zach,

Would your comment that downward force (kick) is the overwhelming
factor in comparison to the area of grip wax also apply to loose snow
conditions? Downward force is the primary factor when the track is
firm and the snow's shear resistance is high enough to resist the kick
force.

When the snow is soft (e.g. new dry snow drifiting into the track) or
where the hill gets turned into marathon powder for the
back-of-the-pack skiers like myself, I lose grip when the snow shears.
I find that I get less grip on soft or loose snow conditions in
comparison to a similar slope inclination with the track packed firm.

If snow grip is limited by the shear strength of the snow, more wax
area would be needed to reisist the same shear force. Wax area could
be increased by either waxing longer (for the same ski width) or using
a wider ski for the same kick wax softness.

With soft powder conditions, I have had to wax softer such that the
kick wax temporarily icing on long steeper climbs with no gliding to
get grip. Then if the wax works just right, the snow build-up breaks
free of the ski when I start gliding after the hill flattens. (When
the ski doesn't free up I'm in trouble).

Edgar

Hi Zach,
I am impressed. You are one of the best when it comes to cross country
technology.
Just my thoughts about your two racers Kris and Justin. Since these two
are well coached I am certain they are skiing the new way which I would
call "power on", so since they are never letting their skis slow down
and change legs way faster then a normal skier they would be needing a
ski that reflexes this technique.
But a average performance skier who is using the normal kick and glide
till it slows is using more down force on his skis if he or she has a
good technique.
I agree 100% weight is a lot if you are skiing several hours and this
type of skier is rare but they do exist.
rw

rw wrote:
J
A skier of 60kg should never ski on a ski which is closed at 100kg and
visa versa.
The skier of 60kg: And here is the kicker::::::: if is a super athlete
and a excellent classic skier.( see now we have to factor in the
persons skiing ability!!!!!) Should buy a ski that closes at 100% of
his body weight. A skier like Joseph who admitted he is not an expert
in classic technique. Should buy a ski that closes at 50kg or even
less. So when Joseph climbs or when he gets tiered he will still be
able to close the ski and have excellent grip.

My "old" skis close at some force/weight less than my body weight. I
don't know where as they have not been measured, but it is obvious from
the way they behave. My new skis close at 100% of body weight. At the
shop, we weighed me with my gear and discussed a bit my plans for
weightloss, etc. We then dialed in the flex machine to 101kg (I weighed
104kg with gear). Each ski was mounted in the machine, and then with
101kg of downforce, the clearance from flat was measured. Marks were
put on the skis where the clearance was 0.0mm (flat to base), 0.15mm,
etc. These define the grip zones for different waxes, klisters, and
temps. The right-left distinction was because the 2 skis are not
identical, my stronger and longer leg got the stiffer one. We also did
the paper under the sole test to confirm.

Now to answer your question (Which is not real world)
For Joseph of course at 100kg he will be faster on the downhills then
any body else because he has more weight behind him.
Yes he could get a wider ski and have more surface for glide and grip
with the same length ski.
The wisdom is more base more glide more grip. Now this is if the skis
have excactly the flex for him. (His WEIGHT his SKIING ABILITY = SKI
FLEX 100kg - 25%= 75kg for a intermediate skier)
I hope this was helpful

Very helpful. This explains why my skis work so well when I use them
properly and am not tired. It also explains why I suffer when I am
tired and my technique gets sloppy.

Joseph

rw wrote:
Anders,
I do not work with a deflection micrometer so I can only guess.
But it looks like
1. The thing with left and right ski is probably just a guide not to be
too concerned about. There is no left and right ski in today's world.

2. of course he will have a short grip zone for klisters. No rocket
science there either.
One applies Klister wax just under the foot. (heel to toe) no more or
the ski will have no glide.

3. the numbers. 0mm = 100% of bodyweight on ski closed
1.5mm = ? 80% of body weight on uphills
2.0mm = ? 70% of body weight grip when he is
tiered
ask him about the numbers I have no clue
rw

Here is a short version of what the number are for: (What they ARE is
clearance in mm from flat under load)

0.05 start dry wax for extra grip, or cold conditions, 2 layers max.
0.1 dry condition wax, 4 layers. This is Normal setup.
0.15 start klister zone for extra good grip, or extra cold.
0.2 normal klister zone
0.3 thick klister zone

These zones obviously overlap, with 0.05 being most forward, and thus
th elongest.

Joseph

kirjoitti:

rw wrote:
1. The thing with left and right ski is probably just a guide not to be
too concerned about. There is no left and right ski in today's world.

I'm quite willing to believe that the Norwegian salesmen weren't out
just to impress and dazzle you with their measuring knowhow and that
the difference was significant enough (and can serve a purpose when
someone has an equally real leg discrepancy).


0.05 start dry wax for extra grip, or cold conditions, 2 layers max.
0.1 dry condition wax, 4 layers. This is Normal setup.
0.15 start klister zone for extra good grip, or extra cold.
0.2 normal klister zone
0.3 thick klister zone

The Swedes leave out the 0.05 measurement and simply advise to stretch
the 0.1 area up to 5 cm forward for very cold conditions.

The recommendation is to wax no more than 3 layers in the 0.1 zone and
then to add one layer per area.

The slight differences are probably explained by differences in
measuring: the Swedish method has the weight "neutral" or balanced
evenly on the feet/foot, whereas Zach wants the weight "forward" or on
the ball/s of the foot - and I'd suppose the Norwegian method matches
his better than the Swedish one (which, for that matter, is more aimed
at the everyman skier, so it's more of a "Keep it simple,
stupid"-method(1)).

(1) OK, there is an even simpler method used by most Finnish
salespersons, where the grip zone is divided into only two areas: one
(for normal waxing, 2-3 layers) where your weight is on two neutral
feet and another (for extra layers or klister waxing) where your weight
is on one neutral foot. (Unfortunately I cannot recall the micrometer
readings used.) This works, too, and is IMHO good enough for up to
decent, maybe even not-quite-semi-ambitious ski marathon races.


Anders

PS a bonus question (to anyone willing to voice an opinion): if normal
wax-of-the-day- hard wax gives you good grip without waxing the entire
length of the grip zone, does it mean that the ski is too soft for you
(even if the measurements were done correctly) - or that the ski can
still be right for you but you should wax the entire grip zone with a
one step colder wax (which would give you the same good grip _and_ a
better glide)?

Yeah Edgar - snow shear in soft conditions is definitely a huge
consideration. Most companies are building skis with a pocket extending
someplace near 30cm in front of the balance point, and 20 or more cm
behind. Under most conditions this is fine. But there are certainly
days where you need to stretch the zone further forward and modify your
technique a bit (don't try to be so forward - drag the foot through a
longer kick motion, etc). I still feel that widening the ski enough to
provide a significant difference in shearing conditions will have four
effects: heavy skis, slow skis, poor handling characteristics, and
better kick. But that's just my own feeling, and certainly geared more
toward high-end skiers who probably have the technical tools to deal
with snow shear in any case...

Z

Kris and Justin are probably pretty good models of the "new way" of
skiing. But I don't think the differences are that great. If anything,
this quicker, more impulsive style of skiing can allow a skier to use a
stiffer ski. The more "old school" long kick and glide technique is
usually coupled with a body position pretty far back on the ski and a
much less impulsive kick. There are a whole bunch of old-style skiers
here in New England - we've got more former Olympians and national team
athletes per capita than most places, and most of them are still
involved in the sport. Some of these guys THINK they want really stiff
skis, because that's what they were on back before ski technology
improved to the point where you can actually have kick AND glide. When
you get these guys on a well-fit modern ski it's usually a revelation.
I've never run into one of these 100% guys. And if I do I'm going to be
REALLY careful not to **** him off!

Z

Z,
Where dit you buy your test bench?
Or did you build it yourself?
rw

I built it. About $900 with a little luck on eBay finding very good
load sensor for $400, and the help of a very patient local machinist.
I'm currently close to $7000 into my next flex tester, with about
another $4000 to go in order to have it ready to go. But it will be
good.

Z