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Incredibly stupid DIN question

post #1 of 12
Thread Starter 

Hola Bears.


I’ve done a few searches on this well-worn topic, but have not found a thread that addresses this query directly.


I may be carrying a substantial load in a pack for the first time in my skiing career. The items, (cameras, lenses, tripod, and etc.,) are very valuable and fairly heavy. The quick question that I have is whether or not to take the added weight, (close to, or maybe even a touch over 20 percent of my body weight,) into account and adjust my bindings accordingly on the days that I carry the load.

post #2 of 12
The short answer may be that you don't need to change anything.  You may be carrying more weight, but chances are your skiing may loose some of its dynamic nature.  The weight increase, may be negated by the "reduction in ability".  Or not !

If you think there will be no change in your skiing despite the added weight maybe a turn of the binding screw would be in order.  Have a binding check done (they are usually free at most shops) and add the weight of the pack  as if it was your normal body weight or slightly less and you should be good to go.
post #3 of 12
Whenever I've skied with a big heavy pack I've skied much more conservatively than when I'm just carrying day tour stuff, so I've never messed with settings to compensate for the added weight.
post #4 of 12
Short answer is no.  The weight in the DIN determination is a measure of your bone strength.  On the other hand if your spend most of your waking hours carrying around an extra 40 lbs, then you should probably include it in your weight.
post #5 of 12
Thread Starter 
  Thank you friends.

The three of you who have posted up here to this point are names that I know well from this forum, and many of your prior posts have proven sage, wise, and accurate. I'll start slowly, and see what develops. 

I most certainly expect my dynamic to change due to the load, and my desire to avoid destroying the cargo and my body parts will make me think, and hopefully behave, more conservatively.

I'm heading out west next week, and have been visiting the websites of the areas I'll be skiing. Looks like coverage is still a bit sketchy and a good percentage of terrain will not be open. Holiday crowds + limited terrain + fewer operating lifts will likely yield long waits for most laps. Thought that I'd dedicate a few days to some moderately serious mountain photography. It would be a breeze to hang out near the park and pipe, but that's not really my speed. Might hunt around for some scenic vistas, or set ups for companions who wish to perform feats of lunatic daring for the lens.

If the snow gods decide to send a few major dumps, then I'll likely leave the pack behind and just ski. On a powder day, I'll definitely leave the cameras behind. Only get a few of those and they are not to be squandered. 
post #6 of 12
Given the tolerances inherent in the DIN system, the weight difference is negligible.  If you take the added weight into consideration, you may go up a point, but the DIN +/-  is two points. I wouldn't bother changing anything.
post #7 of 12
I agree with Ghost.

The reason weight is considered in DIN is because it's an indication of how strong your bones are. Weight that you are carrying is irrelevant. Look at it this way: if you wore a really tall hat, would you increase the DIN because now you're taller?
post #8 of 12
Originally Posted by sjjohnston View Post

I agree with Ghost.

The reason weight is considered in DIN is because it's an indication of how strong your bones are. Weight that you are carrying is irrelevant. Look at it this way: if you wore a really tall hat, would you increase the DIN because now you're taller?

I disagree. It may be part of it, but basic physics clearly says that mass ~ force. Which means that with more mass (weight), at an equal skiing style, you will push a larger force on your bindings.

It may be he goes slower with the extra weight to compensate, but if your ski style and speed stay the same, you will release sooner with more mass at the same DIN.

edit: to make it clearer, consider DIN a value your bindings need to be at to NOT release when skiing. An indication to the bindings that says "everything under X Nm is perfectly fine". That pretty much removes the bone strength aspect.
Edited by Frederik - 12/16/09 at 10:21am
post #9 of 12
The whole point of the binding is to release when a particular force is exerted, because that force is sufficient to endanger your bones.

The amount of force that endangers you doesn't change because you're carrying something.
post #10 of 12
Yes, but there is also an amount of force it needs to withstand when you're skiing. If you ski exactly the same with the extra weight than without it, you will put more force on the bindings with the backpack.

(very) Simplified imaginary number example: DIN 4 = 4Nm to release
making a turn without the backpack on puts 3 Nm on the binding, no issue here.
falling without the backpack puts 4 Nm on the binding, you pop out as you should. DIN at 4 is correct.

making a turn with the backpack on puts 4 Nm on the binding (because more mass at the same skiing style equals more force), now you're getting a pre-release.
falling with the backpack on puts 5 Nm on the binding, you release. Your DIN should be between 4 and 5.

It's all about how much force you put on the binding. Which is the reason why racers sometimes need insane DIN, yet still get releases when they fall (considering it's +- correct, which is very tricky as we all know). Their bone strength isn't double of mine, but their DIN is.

edit: anyway, I'm not advocating to put the DIN higher, I believe you will compensate by skiing cleaner/slower. I just don't agree with the bone strength thing at all, bindings are very basic physics devices with a clear function: don't do anything till X Nm, then release. And F = m.v
Edited by Frederik - 12/16/09 at 12:02pm
post #11 of 12
In the last few words, you get it right: "don't do anything unitl X Nm, then release." The FORCE is the point at which you want to release, not the velocity. What you're suggesting is that what we want to do is hold the "release velocity" constant, so we have to adjust the "release force" to correct for a change in mass. In fact, we want to hold the "release force" constant; there's no reason to adjust anything.

Your binding isn't supposed to release when you fall. You can break your leg standing up on your skis (beginners, in particular, do this more often than is entirely healthy); you can fall without any danger of getting hurt at all. Rather, you're binding is supposed to release when the force (stated in Nm or foot-pounds or whatever unit you prefer) is above the threshold where you think it poses an unacceptable risk of injury.* The fact that part of the reason the force exceeds that threshold is because you're carrying a pack is irrelevant.

In your example: if 4 Nm isn't enough to hurt you, the should not release at 4 Nm, either when you fall without a pack, or when you're skiing with a pack. If, on the other hand, 4 Nm is enough to hurt you, it should release at 4 Nm, even if the reason you're subjecting yourself to the excessive force is because of the pack.
*The way we choose the release force is slightly complicated, for a few reasons, including the fact that bindings are imperfect measurers of force, and that what we're really afraid of isn't an instantaneous force, but a force over some period of time. The primary determinants are:

- How sturdy the skier is physically. Most narrowly, this is a matter of bone strength, at least if one thinks of a bindings in a sligthly old-fashioned way as designed almost entirely to avoid broken legs. In the old days, there were some binding manufacturers whose manuals used tibia measurements as an input for release settings, rather than weight or height. Of course, now that bindings are all fairly successful at preventing broken legs, the more likely injuries are to ligaments, so the problem is a bit more complicated.

- Because bindings are imperfect: how does the particular user balance the danger of pre-release and non-release? There are basically two sub-reasons here, which align:
 * How dangerous is a pre-release? For faster skiers in more dangerous situations, the downside of pre-release is much higher.
 * What's the relative prevalance of shocks (high force / short duration) and slow-twists (moderate force / long duration) that the particular skier is likely to experience? For a fast, accomplished skier, shocks are very common and slow twists rare; for a beginner, the opposite is the case.
post #12 of 12
I see, I get your logic now, nice!
To summarise: while your binding will release quicker with the extra weight, that same force is also going to be applied to your body. So you should keep your DIN the same, ensuring it pops out right before you would get hurt.

I was focussing too much on the pre-release issue and forgot to take the bold part into account.

So, recap: When skiing with a lot of extra weight, put your DIN on your normal value and compensate for pre-release by adjusting your ski style!
(the v, or actually a, in F)
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