|
Winter, 2002-- For some time we have been wanting to
develop a series of bench tests to quantify certain freeheel
binding performance parameters. There are many choices out there
these days, with a number of different feature sets appealing
to a wide range of skiers. To date, all of the reviews and most
of the published performance information has been based on subjective
observations. We have tried to get as much feedback from as many
skiers as we can, but we feel the time has come to gather some
hard data concerning what has been referred to as the last part
of the tele gear puzzle, freeheel bindings.
The test results below reflect
the first two bench tests we have devised for acquiring that
data. One, the "rocker launch" test is an obvious choice
for this first report, it's an issue that has been much discussed
on our Telemark Talk Forum, and elsewhere. The other initial
test is for what we call "forebody pressure." It is
an attempt to nail down some figures that relate to how active
a tele binding is in transferring edge pressure to the front
half of the ski.
|
|
Test 1: Forebody Pressure
There have been two schools of
thought in modern tele binding design, there are those who think
a binding should be as "transparent" as it can be,
basically disappearing and allowing the boot to find its own
flex, the flex the designer built into the boot ( see our interview with Garmont product manager
Paul Parker). Another view is that with today's stiff plastic
tele boots, a more active binding, one that helps the boot break
at the bellows and one that aids in keeping the skiers forefoot
closer to the rear ski deck, is a real plus. In "transfer
of forebody pressure", we feel that we are introducing a
third important new concept in freeheel binding design theory.
First some ski technique theory as background:
In alpine skiing a balanced stance
is achieved in the turn iniations phase by pressuring the front
boot cuff with the shin. In both telemark and alpine skiing we
try to get ski forebody pressure early in the turn by adjusting
our fore and aft position and by relaxing our ankles. One of
the biggest challenges in freeheel skiing is to get more of the
ball of the foot down on the rear ski and use the power of the
flexing boot bellows to crank on the needed forebody pressure.
Alpine skiers can simply drive their shins into the boot tongue
during the early part of the carve and immediately reap the rewards
of the resulting pressure increase along the forward part of
the ski edge. In freeheel mode, try that on the rear ski with
with a passive binding and much, if not all of the force will
be lost as the heel just comes up higher and the boot rotates
up onto the toe.
Many experienced and talented
tele skiers have found the solution in subtle yet precise adjustments
to their stance, as well as through the use of ankle flex. These
skiers may indeed prefer a less active binding, one that engages
the boot much later, allowing them to dictate edge pressure characteristics
themselves. Others, both old hands looking for maximum control,
through more forebody pressure than can be obtained using traditional
techniques, and skiers looking for more help from their gear,
may prefer an active binding, one that transfers more shin pressure
onto the forward edges.
At what point does a binding
become too active, or for that matter, how passive is too passive?
That's the big question isn't it? For sure this will vary according
to personal preference and intended use, but interestingly the
binding that scored the lowest on our bench test was also the
one that was universally dogged the hardest in last season's
subjective testing.
Of course it's important to keep
in mind that forebody pressure is just one of several tele binding
parameters. Individual skiers have to decide for themselves how
important each of these qualities are for their own style and
needs. That being said, we feel that this new test tells us a
lot about what to expect on the snow from a given model. OK,
enough background, let's get to the methodology and the results.
 |
|
Methodology: Coming up with a device that accurately
measured forebody pressure while removing as many variables as
possible was more difficult than it seemed like it would be.
Some of the issues we struggled with included the position of
the weights, how much weight to use and how low the simulated
knee drop should be. But by far the biggest challenge was finding
the proper material to simulate a human foot in the boot. Flexing
an empty boot just didn't cut it, the boot was too easily distorted
and it would flex in unnatural ways. We tried packing the boot
with various materials before filling the liner with beach sand
and a piece of lexan cut to approximate the basic bone structure
of skier's foot. This final approach worked great.
Special care was taken to make
sure each binding was mounted with the pin holes aligned on our
simulated "chord center" mark and that the clamp-in
pressure was adjusted to to provide a medium amount of spring
preload. The cord leading down from the front of the weighted
arm served to standardize the amount of "knee bend." |
|
We ended up using 40 lbs of weight and
a sand filled boot. |
|
|
The Forebody Pressure Results,
in pounds
|
Binding |
Piv 1 |
Piv 2 |
Piv 3 |
Piv 4 |
Piv 5 |
none |
|
 |
Notes: Readings were taken for each pivot
position available on the 4 tested models where this is an option,
including the "no pivot" condition that can be used
with the HammerHead.
The "Riva Z comp" is an '02/'03
Riva Z with compression springs like the Cobra.
The Bishop binding for 2001/2002 was included
since that is the Bishop we tested this season. We have received
next year's model with the redesigned toe block and the new forebody
pressure numbers are included in the table. There is no question
that the new Bishop toe block engages the boot much earlier,
resulting in a total change in its characteristics. The Bishop
went from being the most passive binding in the test to one of
the most aggressively active. We are looking forward to conducting
further on snow testing of the Bishop.
|
|
Addendum to the forebody test:
One thing we need to
mention is this, forebody pressure and heel retention can be
increased or decreased fairly easily in most bindings, at least
to a certain extent, by adjusting the "clamp-in" pressure,
thereby putting more or less preload on the spring(s). We have
used this approach to increase tourability (less clamp-in pressure)
or downhill performance (more clamp-in pressure) many times.
On bindings like the Linken or the Cobra this is easier to do
because they have registration markings that make it clear how
the thing is set up. The O2, for example, does not. This makes
it difficult to know exactly where to dial in the spring preload
for either touring or downhill performance. Each change involves
a bit of guesswork, even trial and error. Markings along the
cable where it enters the spring cartridges would be an improvement.
Is this a valid way to approach
increasing or decreasing ski forebody pressure? Does it work
as well as movable pivot points? That's a tough question. It's
certainly one way to do it, but users need consider the downside
to increasing spring preload to improve performance on the descent.
Essentially, when you increase preload tension you are decreasing
spring travel, making it harder to get into the binding and adding
to the possibility of component failure. That being said, many
skiers have enjoyed success and increased performance cranking
their bindings down to the point where they can barely get into
them, all the while managing to avoid breaking anything. At this
point, adjusting spring preload to control the transfer of forebody
pressure (or heel retention) is probably most accurately viewed
as a "work around" rather than a final solution. Will
we someday see a simple, lightweight freeheel binding with a
straight-forward, lever action, "on/off", uphill/downhill
control adjustment? Perhaps.
How Does A 3 Pin Binding Compare?
|
How do the figures above compare
to a traditional 3 pin binding? Just how active is this venerable
antecedent of its more high tech descendants? Our old Black Diamond/
Chouinard HD 3 pin turned in a surprising performance.
With a measured 29 lbs at
the scale, the 3 pin
proved to be almost as active in applying forebody pressure as
a Targa! We were indeed surprised until we took a close look
at what was going on. As can be seen in the bottom photo on the
right, the 3pin nails the duckbill down hard to the plate. The
measured force appears to be coming from the bend in the duckbill
as the binding is obviously doing nothing with the boot bellows.
Would this forebody pressure we see in the test be as great in
actual use? We don't know, but assuming that the skier gets greater
ball of the foot pressure than our test rig is applying (maybe
a big assumption in many cases), there would be less bending
of the duckbill, and perhaps less forebody pressure. We won't
know for sure until we move forward with a couple of new tests
we are developing, including one that will be designed to measure
the effect of technique and stance on forebody pressure. |
|
|
Test 2: Rocker Launch
Warning: many of you may want
to just skip this test completely, others will read it carefully
and with great interest. Such is the nature of the sometimes
dreaded phenomenon known as "rocker launch." For many
tele skiers, especially lighter weight riders, rocker launch
has evolved into a real concern. Others insist that it's all
in the head. Some have even written on our Forum that the rocker
launch folks are "off their rocker." But maybe not. |
|
|
For example if it takes 60 pounds
of weight to get a single boot down onto the ski and the skier
weighs 145 lbs, in parallel mode that skier may have a problem,
needing 120 pounds of force just get both heels down. The skier
in our example very well may feel that he is being thrown forward,
or "launched" toward the ski tips by the rocker in
his boots.
Binding manufacturers have tried
to address this situation in several ways. For a number of years
Voile has offered a wedge that fits under the binding plate to
help the binding conform to the boot's rocker. One manufacturer
has begun to make bindings with higher toe bars, allowing more
room for the upturned duck bill. In our experience the biggest
single factor contributing to rocker launch (outside of the boots
themselves, of course) is a heel piece that is too low. Especially
a heel piece that is lower than the binding plate itself. When
this is the case the boot bellows has to open up even farther
than it does when just sitting flat on the floor. Combine a low
heel piece with a low toe bar and it will take a lot of weight
to get the boot heel down.
Of the two factors--low toe bar
and low heel piece--we feel that the latter is a bigger issue.
Observations have shown that the force required to get the heel
down while the bellows still has some easy flex is very small.
Past a certain point and whoa Nellie, you are not just asking
the bellows to open up, you are asking it to stretch! This requires
a lot of weight. It also puts significant force on the binding
toe bar. One binding maker told us about a year in which their
main model had a heel piece that was lower then the binding plate.
They had a lot of toe bar breakage, including metal fatigue,
resulting in cracks right across the middle of the bar! The following
year they introduced a higher heel piece.
Happily, if you are a lightweight
skier and bothered by rocker launch (something that does not
apply to any of the Tt.com crew, even 112 lb. Laurie says "why
do you want to be on your heels anyway?"), correcting the
problem may be as simple as raising the height of your heel piece.
How much? That's another good question. I would start with a
heel piece around 5mm higher than the binding plate. The O2 uses
about 10mm of rise and it works well as far as reducing rocker
launch but some may find the differential to be too much. Others
may find it just right but I would work up to it.
Or you could forget about shimming
your heel piece and try a binding like Voile's VP-II or Bishop's
Bomber with their articulating toe bails. Or maybe just go see
a shrink (only kidding!). |
|
|
Methodology: This was a simple test to conduct. We
used a boot with a medium amount of rocker (other boots may give
different numbers but the relative results should remain the
same), we set up each binding with a standard amount of clamp-in
pressure, then we added weight until the boot heel just began
to contact the manufacturer's standard heel piece. The results
are in the table at right, expressed in pounds. |
 |
|
|
Conclusion: As mentioned previously, these bench
tests measure just two of the factors that affect freeheel binding
performance. We expect to devise more tests in the future, input
is always welcome. These kinds of tests are meant to be taken
as descriptions of certain binding features (active or passive,
for example), not prescriptions for individual skiers. There
are a number of important binding features beyond forebody pressure,
or ability to deal with rocker launch, that skiers should legitimately
consider, release, step-in, rigidity and durability, to name
just a few. Our hope is that you the reader can combine some
of the hard data above with our subjective tests, as well as
your own demo experiences (whenever possible) to help you select
the best binding for your individual style and needs
|
Cover | Site
Map |
News
Page
| Talk
Forumx| .Dr. Telemark
|