The Numbers Game: Bindings, Part 2

[pchewn]

Thanks pchewn. I think I understand the math--what I'm having trouble imagining is how are the parts of this system are related spatially. To stay with physics, how would we draw this as a vector diagram? Where is the force applied? Where is the pivot point, or fulcrum? Thanks again.

This picture is the best one I found online. The torque is shown. The pivot point is the back of the heel of the boot. The force is applied (very near) to the front of the bool. The distance between pivot and force is approx equal to the BSL.....

 

[PisteOff]

This picture is the best one I found online. The torque is shown. The pivot point is the back of the heel of the boot. The force is applied (very near) to the front of the bool. The distance between pivot and force is approx equal to the BSL.....

The arms on the test machine push against the toe-box, pivoting the boot at the heel piece until it releases. It gets tested in both directions. To test the heel release a strap goes under the heel of the boot attached to two arms, one on either side of the boot, and they raise the boot up at the heel until the binding releases. Pivot point being at the toe piece. I am sure there is video of the procedure online if you look for it.

 

[PTskier]

Over age 50? Dial the setting back:
"The mineral content of bone (also referred to as “mineralization” or “ash content”) increases with age, and classic studies have shown that the breaking stress of bone increases exponentially with ash content, while the toughness of bone (resistance to fracture, or the inverse of brittleness) declines as the ash content reaches a maximum"
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2991386/
There is no magic about age 50. The process is gradual. A point to change the setting has to be set somewhere, and the lawyers and insurers chose 50. The fact of bone weakening with age is a fact, sez the National Institutes of Health and other sources.

The chart is designed to estimate bone density based on body size. It isn't perfect, but it works pretty darn well.

Yep. In olden days, pre-DIN, some binding maker (Marker?) had a caliper that measured the top of the tibia and used that size as part of the setting chart. That didn't take into account bone density, just bone size which will be representative of bone strength except for the loss due to aging.

I have my guy set them to the chart and then I put them where I want them.

OK for you. Others should set them by the chart unless they chose to deviate due to experience otherwise. I set mine .5 less than the chart, and I like the result--for me.

Inadvertent release has more than one factor. The spring setting is one factor. The retention ability of the binding is another--how far can the boot get out of position and the binding pull it back into position...more is better. And, related to cheaper & lower level bindings vs. costlier & higher level bindings, are the bindings not yet showing wear or damage? Cliff jumpers and mogul slammers need differently built bindings than green run cruisers can get by with.

Very interesting article from Vermont Ski Safety: If my bindings are releasing inadvertently, how much should I crank them up?
https://vermontskisafety.com/ufaqs/...nadvertently-how-much-should-i-crank-them-up/

And, what can be done with sticky bindings that don't move well? Can a good shop that handles that brand take them apart, clean them, lube them, reassemble and test them so they work like new? I've seen Marker & Rossi bindings on friends that need something done to them.

 

[Lauren]

Thanks pchewn. I think I understand the math--what I'm having trouble imagining is how are the parts of this system are related spatially. To stay with physics, how would we draw this as a vector diagram? Where is the force applied? Where is the pivot point, or fulcrum? Thanks again.

With my amazing artistic abilities, here's a very basic vector diagram of how skis are tested:
2 tests. Test 1 (first diagram below), a force is applied onto the leg, the pivot point is at the toe, and the heel releases. Test 2 (second test), an arm is put onto the leg to create a torque at the heel, and the toe will release.

The torque is where the force is applied, not at the pivot point (because that is the amount of torque that is on the leg of the skier).

 

[cantunamunch]

The torque is measured where the force is applied, not at the pivot point (because that is the amount of torque that is on the leg of the skier).

I will say it again - what is being measured is *not* what is being prevented.

What is being measured are the torques the boot can put on a ski, with pivot points at the heel and the AFD. Those are shifted and represent a maximum binding-allowable reaction to an external force and torque - coming from outside the binding, with a pivot at the tibia (or other point appropriate to the release direction).

That external force is itself a reaction to the inputs the skier applies to the snow (or rock or tree).

It's important to keep all those levels of indirection straight, otherwise cause and effect are hopelessly scrambled, let alone frames of reference.

 

[Lauren]

I will say it again - what is being measured is *not* what is being prevented.

What is being measured are the torques the boot can put on a ski, with pivot points at the heel and the AFD. Those are shifted and represent a maximum binding-allowable reaction to an external force and torque - coming from outside the binding, with a pivot at the tibia (or other point appropriate to the release direction).

That external force is itself a reaction to the inputs the skier applies to the snow (or rock or tree).

I'm pretty sure we're saying the same thing. Although reading my description again...I probably could have chosen better words. It's the reactionary torque to the measured torque, which is equal to the measured torque. I took the word "measured" out of my description.

 

[cantunamunch]

Probably - I just wish I had time and talent to draw all that in one diagram. The previously posted pictures show the testing well, but that's about it.

 

[PisteOff]

OK for you. Others should set them by the chart unless they chose to deviate due to experience otherwise.

Agreed. There is much about this sport that is personal choice. Everyone is different and should do what is best for them. Binding settings are only one of many important decisions we make as skiers with regard to our safety.

I will say it again - what is being measured is *not* what is being prevented.

True, and the forces applied during testing are little like what the ski/binding/boot combination endure on the mountain.

 

[pchewn]

With my amazing artistic abilities, here's a very basic vector diagram of how skis are tested:
2 tests. Test 1 (first diagram below), a force is applied onto the leg, the pivot point is at the toe, and the heel releases. Test 2 (second test), an arm is put onto the leg to create a torque at the heel, and the toe will release.

The torque is where the force is applied, not at the pivot point (because that is the amount of torque that is on the leg of the skier).

View attachment 39817

The machines that I'm familiar with test the binding in this way.

 

[Bruno Schull]

Two videos/two methods

This video shows an automatic testing machine. It seems to work like the picture above with the blue corrections.


This video shows a manual system. It seems to work like the original picture above without the correction.


Interesting differences/approaches to testing bindings.

What's the history here? What is considered superior?

 

[Guy in Shorts]

9 and under
50 and over

Yes....you are getting a setting “back” up the said “chart”.

Yes....it pisses most 50+ year olds off....but it is what it is. You don’t like it...change it yourself to your desired setting. Just know, my “ski tech sign off paperwork” is now void.

Call myself a type 3+ skier with the plus offsetting the age penalty. My DIN remains where I want and the paperwork can can be signed off properly. Everyone is happy.

 

[cantunamunch]

What's the history here? What is considered superior?

The machine in the first video was developed to save the techs the time suck of having to use the manual equipment of the second video.

https://vermontskisafety.com/vermont-ski-safety-equipment-inc/vermont-release-calibrater/

What is superior depends on how much workload and how much up front capital the shop has

 

[pchewn]

Two videos/two methods

This video shows an automatic testing machine. It seems to work like the picture above with the blue corrections.


This video shows a manual system. It seems to work like the original picture above without the correction.


Interesting differences/approaches to testing bindings.

What's the history here? What is considered superior?

The manual system attempts to put a pure torque on the boot. Applying a pure torque is difficult to do. For example when checking the toe release, a pure torque will not result in any net sideways force. But clearly by watching the video, the operator is applying both a sideways force and a torque. USING THIS METHOD, YOU HAVE TO DO SOME MATH TO GET THE DIN SETTING FROM THE TORQUE AND THE BSL.

The automated system puts a linear force on the boot and allows the boot's pivot point to convert this to a torque. This is (probably) more repeatable and consistent. USING THIS METHOD, YOU DO NOT HAVE TO DO MATH TO GET THE DIN SETTING. IT CAN BE READ DIRECTLY FROM THE FORCE TRANSDUCER AND DOES NOT DEPEND ON THE BSL.

I found it interesting that the 1st video showed a toe release where the toe never moved far enough to provide an actual release.
I found it interesting that the use of proper terminology was confused in the videos. Pressure is not force is not torque -- they are each very different mathematical concepts. [I used to have a great interview question for mechanical engineers: Please explain the difference between Stress Strain Strength and Stiffness]

 

[Bruno Schull]

Some time back over at Wildsnow there was a very interesting post and discussion about bindings and release functionality. It included testing, comments, and color, from Rick Howell of Howell Ski Bindings.

https://www.wildsnow.com/15123/tech-binding-release-testing-acl-broken-leg/

I learned a great deal from that post and the comments that followed. First, it's way more complicated than I thought. Second, it's possible that alpine bindings do a better job or protecting your lower leg bones from breaking but don't protect your knee soft tissue that well, while most traditional pin bindings might do a worse job of protecting your bones but a better job of protecting your soft tissue.

For anybody interested, I think it's really worth reading through the comments.

And as to my original question...thanks again for all the comments. There's an amazing community here. I appreciate the help.

Bruno

 

[Marker]

You can punch the toe all you want so long as it doesn't interfere with the boot binding interface. You aren't changing the boot BSL at all. Someone puts their 28.5 foot in a 316 (31.6cm) BSL boot. They punch the toe 3-4mm for some room. The BSL is still 316 even if the 'foot container' is now a bit longer.

I get that the BSL doesn't change, but if the toe is punched 3-4 mm or even more, won't you reach a point where you do interfere with the toe/binding interface?

 

[François Pugh]

BSL=500 (unreasonably large) has twice the moment arm as a BSL=250. Therefore, to get the same torque, the force (heel or toe) will have to be 2X as much on the BSL=250

It's math.

Torque = Lever arm distance X force Torque is what breaks the leg. Therefore, if you want the same torque you need to change the DIN setting (force) for changes in moment arm (BSL). Like this:

Let's say you want 50 N-m of torque for the release point for your toe setting.
For a 250mm (.25m) BSL. Your binding will be set at 200N 50N-m = .25m X 200N and that is approximately DIN 6.5

For a 500mm (.5m) BSL. Your binding will be set at 100N 50N-m = .5m X 100N and that is approximately DIN 3.25

Just think of the boot sole length as the length of the wrench that's trying to break your leg, and the DIN number as how hard someone has to push on the end of the wrench.

 

[Bruno Schull]

OK, stupid question.

I've been looking at the table previously linked in this thread https://www.pugski.com/threads/din-settings.7994/page-2#post-207660

(By the way, thanks for your analysis pchewn...much appreciated)

In this table, I see height, weight, and BSL. I do not see how the skier type (I, I, II) is taken into account. How do you read this chart, and incorporate your skier type?

Many thanks,

B

 

[François Pugh]

IIRC, that chart is from 1996. Find a newer one with instructions. You move down one line to increase skier type. Also IIRC the numbers there (without correction by moving down) are for type 1.

 

[Bruno Schull]

Thanks--that make sense now.
Bruno

 

[karlo]

Just yesterday,I had my bindings, on a ski I am taking out of retirement checked. The shop used a Wintersteiger (spelling?) machine. A DIN number, or setting number, the one the bindings after set to, is entered into the machine. For the toe, torque is applied and the result shows up on a colored bar, green at its center, yellow at either end, red at either of the far ends. If the needle is in the green zone, then the toe binding is providing the necessary torque for a setting, in my case 8 when going by the book.

One toe piece, torque to both sides was in the red, on the side of excessive resistance. The setting was reset one step lower, to 7. Torque to one side was now green, relative to the 8 inputted into the machine. Torque to the other side was still red. Then, the tech did what he called a "full" torque test to each side. Both came up green and the tech said I was good to go.

Anyone know what the difference is between two torque tests, one "fuller" than the other? And, should I trust the "full" test if the other test fails?

I normally set higher than by the book. But, now that I don't know what to trust, I'll start low. If I get pre-releases, I'll set higher, bit by bit. But, still, I wonder if I will be safe.