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Origin of the 3-Piece Boot

post #1 of 10
Thread Starter 

Interesting article on the origin of the 3-piece boot design (e.g., Full Tilt, Dalbello cabrio), with categorical statements on ankle flex:

 

https://www.skiinghistory.org/history/origin-three-piece-ski-boot

post #2 of 10
Cool. Thanks for posting!
post #3 of 10
Really interesting. Having skied Dalbello's for years, have some trouble with the "push back" idea; always seemed as if the boot was forward flex friendly to a fault - but will mull it over. Maybe the superior shock absorption was about push back, like a cambered ski being smoother. Also the bit about ankle flexion for fat intermediates is surprising. Thought some ankle flex was desirable. Any instructors want to comment?
post #4 of 10
Thread Starter 

The article didn't seem entirely coherent to me. If there's too much "push-back" with the boots, how can there also be too much forward flex? (I ski Dalbellos, too.)  I'll message Bill Haight, who posted that article on FB (and who fitted my Dalbellos) to see what he says. 

post #5 of 10
Quote:
Originally Posted by lakespapa View Post
 

The article didn't seem entirely coherent to me. If there's too much "push-back" with the boots, how can there also be too much forward flex? (I ski Dalbellos, too.)  I'll message Bill Haight, who posted that article on FB (and who fitted my Dalbellos) to see what he says. 

 

Correct me if I'm wrong.    It sounded like

 

1) "push back" was triggered by (excessive?) forward flex so the forward flex is the cause and push back is the effect

 

2) "push back" actually meant 'force against the ankle' and, by Newton's third law, an equal and opposite force on the ski relative to the racer's body, which (the ski has far lower mass), accelerated the ski forward.

 

So the causation chain is something like

more forward flex in boot->

skier flexes trying to get forward, loads up the tongue spring->

tongue spring pushes back against ankle->

ski squirts forward in equal and opposite reaction ->

skier is in back seat.

 

Yes, I am picturing the tongue as a leaf spring here.    

Moving on to your question, you are absolutely right that having a stiffer or softer spring doesn't really change the causation chain above; having a stiffer spring merely moves the entire cause and effect train into a smaller range of ankle motion.      

 

But if we lock out part of the spring (of whatever stiffness) with a completely rigid element we've removed that range of motion.    And we've therefore limited the amount of force the boot can exert on the ankle and ski.

It may be easier to visualise the force/amount of motion relationship if you think of the spring as a coil spring instead of a leaf spring.    It doesn't matter if you change the stiffness of the spring; but slide a rigid rod a given amount inside the spring and you've locked out a certain amount of motion and limited the amount of force the spring can exert.

post #6 of 10
Thread Starter 
Quote:
Originally Posted by cantunamunch View Post
 
Quote:
Originally Posted by lakespapa View Post
 

The article didn't seem entirely coherent to me. If there's too much "push-back" with the boots, how can there also be too much forward flex? (I ski Dalbellos, too.)  I'll message Bill Haight, who posted that article on FB (and who fitted my Dalbellos) to see what he says. 

 

Correct me if I'm wrong.    It sounded like

 

1) "push back" was triggered by (excessive?) forward flex so the forward flex is the cause and push back is the effect

 

2) "push back" actually meant 'force against the ankle' and, by Newton's third law, an equal and opposite force on the ski relative to the racer's body, which (the ski has far lower mass), accelerated the ski forward.

 

So the causation chain is something like

more forward flex in boot->

skier flexes trying to get forward, loads up the tongue spring->

tongue spring pushes back against ankle->

ski squirts forward in equal and opposite reaction ->

skier is in back seat.

 

Yes, I am picturing the tongue as a leaf spring here.    

Moving on to your question, you are absolutely right that having a stiffer or softer spring doesn't really change the causation chain above; having a stiffer spring merely moves the entire cause and effect train into a smaller range of ankle motion.      

 

But if we lock out part of the spring (of whatever stiffness) with a completely rigid element we've removed that range of motion.    And we've therefore limited the amount of force the boot can exert on the ankle and ski.

It may be easier to visualise the force/amount of motion relationship if you think of the spring as a coil spring instead of a leaf spring.    It doesn't matter if you change the stiffness of the spring; but slide a rigid rod a given amount inside the spring and you've locked out a certain amount of motion and limited the amount of force the spring can exert.


That makes sense, I think, at least in theory. Though in practice, at a 110 flex (a soft boot, granted), I don't notice this effect.

post #7 of 10
Quote:
Originally Posted by lakespapa View Post
 
 


That makes sense, I think, at least in theory. Though in practice, at a 110 flex (a soft boot, granted), I don't notice this effect.

 

You're in a cabrio boot?

 

 

IMO just shifting the tongue to sit outside the boot would make a big difference- like changing from a doubly-fixed leaf spring to one with a shackle.     

What fascinates me is the implications for tele and 3pin XCD  boots - the one thing you do *not* want to do when fakeamarking is try to get ankle-forward in the "press your shin against the tongue" alpine sense.

 

post #8 of 10
Thread Starter 
Yes, cabrio. I'm not understanding what's meant by shifting the tongue outside the boot.
post #9 of 10
Thread Starter 
Oh, wait. Maybe I do. But if I want to avoid push-back, why would I do that?
post #10 of 10
Quote:
Originally Posted by lakespapa View Post

Oh, wait. Maybe I do. But if I want to avoid push-back, why would I do that?

 

Because the top of the tongue is then more free to elongate, without being pinned between liner and shell?

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