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Fore-aft balance

post #1 of 14
Thread Starter 
This is a just a tip for somebody considering a heel lift ramp, or delta change to get their upper body cg over the sweet spot of their ski.

Traveling down your favorite terrain steepness, do you feel you shin makes enough tongue pressure to make your turn, or does it build to too slowly or require you to make a compensation move forward on your skis using lots of muscle. If so, you might want to consider a heel lift, to move your shin closer to the boot tongue.

To get the right amount of tongue pressure for the steepness you want, the right size heel lift will accomplish this. However, it is also going to move your upper body more forward on your skies, and you may or may not want this. Remember your hip inseam (representing your upperbody cg location) should align over your foot instep (where you want to feel the pressure on your foot). If the heel lift shim has moved your cg to far forward (tiring calf muscles in your lower leg) you can move your cg back, and still maintain the tongue pressue you established with heel shim, by using a delta binding toe lift shim, that will maintain this same tongue pressure acheived with the heel lift, and put your cg back where you want it, to maintain a powerful postion in a turn.

Works great for me, for powder and off trail, I take the shims out.

I checked my ideas here on paper, and doing this sort of thing for a living, I tought that this is what fore-aft boot balancing will come down to for a guy like me.
post #2 of 14
Jason,

Are talking about an external to the boot shim (sole of the boot) for for/aft alignment? If so, it is only relevant to the particular binding make and it can't be removed for a different binding delta angle.

RW
post #3 of 14
Jasonhawk54,

How does a heel lift cause or create more shin pressure?
post #4 of 14
Thread Starter 
I should have said "for Powder and off trail I take the heel lift out from underneath my boot liner." In my case, I used a 3 x .04", (1mm)thick, black ABS plastic sheet, cut to the shape of the heel portion of the bootbard, identcally stacked on top of each other. I also used this same plastic as underneath the toe binding (additional screw length reqd), 2 x .04" thick.

The insight was that by using a heel lift my bodies cg went forward towards the ski sweetspot, and also moved my knee forward, where my shin moved forward in the boot cuff that has a fixed forward lean. So my lower leg is more toward he tongue side of he boot, given the fixed position of the shell and forward lean. The boot shell is fixed volume in the same position, and my higher foot ramp is causing my lower leg and knee to go foward relative to it. (ideally my body cg will now be right over the ski sweet spot) This distance reduction actually determines the additional amount of boot tongue pressue desired. However, in my case, I felt too far forward because my calfs were smoking and my upperleg was vertical and doing little work. The second insight was that I discovered adding the right size toe shim would move my cg back to where I wanted it. By doing this, I found, the tongue pressue was the same because a toe lift is a delta change, and a delta change moves my cg back but maintains the same geomerty relationship between forward lean of the boot, ramp angle. My lower leg and my boot are moving together in a delta change, that repositions my upper cg, but keeps my shin to boot tongue distance the same as before the delta change, which determines the tongue pressue. In a delta change the ramp and forward lean (effective) change the same amount and orientation as the delta.

The heel lift also made ski taller, and happen to improve the boot fit, and put my upper leg in an (almost) vertical position, where the delta moved me back a bit and my calfs gave the work back to my quads, so both were happy, during a hard turing. In summary, my cg under inertial forces during skiiing found the most direct route (load path) to the boot, and save muscle work to hold the positions. For me this worked but I wouldn't say this approach for everbody, because any change can produce a different result in another persons stance or boot fit.
post #5 of 14
JH54--Thanks for your comments. I have two questions.

First, I want to second Bud's question to you:

Quote:
How does a heel lift cause or create more shin pressure?
If adding heel lift creates more shin pressure, wouldn't women with high heels (and no boot tongues to lean on) tip over?

Second, what is the effect you are trying to create by adding shin pressure in the first place? I, along with some others here, have often argued that shin pressure is over-rated, that it does serve a purpose, but that the purpose it serves (the effect it causes) is not something I'm often looking for. What is your opinion on that?

[Warning--this topic is fraught with challenge and polarized opinions!]

Best regards,
Bob
post #6 of 14
My understanding is that a heel lift within the boot is typically used in cases where there is not enough dorsi-flexion in the ankle to acommodate the forward lean of the boot. The symptom of the problem is that the boot holds the ankle fully closed, so there is no additional range of motion to flex. By lifting the heel, the ankle is opened a bit, which provides additional ROM to flex.

To answer the first question, lifting the heel is not done to cause more shin pressure, it is done to enable more shin pressure to be applied as the rider sees fit.

If the rider truly is forced into a closed position by the boot, that would be a bad thing because the only possible flexion option would be at the knees, rather than the ankles. So absortion of terrain (or flexion for any other reason) may tend to put the rider in the back seat. This option restores proper ankle flexion to enable a balanced stance in all conditions. Of course, the point of forward lean in the first place is to enable deep knee flexion without putting the rider out of balance, so depending on the boot (and the anatomy of the rider), it may be that additional ankle flexion is unnecessary. That said, I would still think you would be susceptible to shin bang if you had zero ankle flexion.
post #7 of 14
Thread Starter 
Quote:
Originally Posted by Bob Barnes View Post
JH54--Thanks for your comments. I have two questions.

First, I want to second Bud's question to you:



If adding heel lift creates more shin pressure, wouldn't women with high heels (and no boot tongues to lean on) tip over?

Second, what is the effect you are trying to create by adding shin pressure in the first place? I, along with some others here, have often argued that shin pressure is over-rated, that it does serve a purpose, but that the purpose it serves (the effect it causes) is not something I'm often looking for. What is your opinion on that?

[Warning--this topic is fraught with challenge and polarized opinions!]

Best regards,
Bob
Bob, I have no experience being in high heels, glad to say, but you will find they lean back to keep their cg over their feet. In skiing a person is statically balanced with their cg forward over the sweetspot of the ski, and the tongue pressure from the boot provides the an opposite moment (torque or force) to balance them in this position, otherwise the skier will fall forward. This is all the tongue pressure is trying to achieve for me. Statically, this can be seen in a side view of a skier, but dynamically the principle is still at working, but is not obviouis by all that is changing in position and rates of speed, that would provide a similar force holding the skier up, equivlent to the static tongue push from the binding.
post #8 of 14
Quote:
Originally Posted by geoffda View Post
....By lifting the heel, the ankle is opened a bit, which provides additional ROM to flex.... To answer the first question, lifting the heel is not done to cause more shin pressure, it is done to enable more shin pressure to be applied as the rider sees fit.
Exactly. Nicely said .
post #9 of 14
Thread Starter 
Quote:
Originally Posted by bud heishman View Post
Jasonhawk54,

How does a heel lift cause or create more shin pressure?

I re-read what I wrote, and without creating a diagram of my geometry that shows how the distance between your shin and tongue is reduced if your cg goes more forward, using a heel ramp in your boot, I will say (which is the right way to show it) ideally, from an efficiency persptective, your cg is over the sweetspot while the tongues of your boot, feel to have the right amount of pressue and hold you up comfortably in this tall, aligned, stance for the type of steepness of the runs you like. if you want to arrive in this position for skiing-is up you, as for as the means of getting there, their are many- A good fit right out of the box, a little ramp change, or a delta or both.

A simple test would be to stand in your shells on your bootboard and add heel shims under your liner, with your cg over the sweet spot of your skis, while somebody measures the distance from your shin to the shell. Add a little more heel lift, and have sombody measure again. If you like me, my shin gets nearer the plastic shell.
post #10 of 14
Quote:
Originally Posted by jdistefa View Post
Exactly. Nicely said .
Yep. Boot setup is extremely situational; dependent on not only the skier's alignment in all planes (fore/aft and lateral) but also on a skier's preferences.

Heel lift doesn't work for all skiers, just like toe lift doesn't work for all skiers. If you took 10 skiers and set them up properly in the fore/aft plane the decision as to how much, what direction, and where the adjustments (lifts - internal and external, fore/aft cuff alignment, boot board angle, etc) should be to allow for a non-locked ankle joint and proper fore/aft balance; would likely be different for each skier.
post #11 of 14
Thread Starter 
In my case I have lots of flexibility (ROM) of my ankle to shin joint, and I can see how limited range of motion would prevent a skier from getting forward and being able to press on the boot tongue. A heel lift moves their their available range of motion forward, that can now collide more deeply with the boot tongue, to control the amount of pressure. However, their taller, basic neutural stance cg, is now more forward. This new cg location relative to the ski sweetspot should be considered.

If I could have found another boot that fit my foot to purchase, that had less forward lean and more ramp, would have given me a better fore-aft balance fit, without a heel lift or toe shim.
post #12 of 14
I've been working on improving my fore-aft balance my last several times skiing. I think my boot setup is close. Meaning, I have a moderate ramp angle (3 degrees), reasonable forward lean (14 degrees) plus about 3.5 mm of binding delta. I have plenty of dorsiflextion and I don't need heel lifts.

Although I played with adding/removing a 1.5 mm shim under my toe today, the conclusion I am left with is I need to continue working on my technique first. It is getting better, but I still struggle with the skis jetting out on steeper terrain, or more mild terrain when I get lazy or tired. I guess I am not convinced there is a magic boot setup pill that will fix that. Kinda like performing root cause analysis.

But, I'm keeping those toe shims in my pocket for the next trip out
post #13 of 14
Thread Starter 
My egg head analysis is based on the 'assumption' my cg goes forward and not up with the introduction of the heel lift, this explains why my shin gets closer to the boot tongue. If you assume the cg (com) does go up then the shin doesn't move forward. But this is all too complicated already b/c I don't know what happens for myself in reality so.. I could be okay with just a toe shim (delta lift only), I mean for me a non-expert skier, might not even matter much... its a matter of where I balance on the ski relative to the center of the radius that giving the feeling I want. My goal was trying to get to use less calf effort, by more tongue pressure. The ramp gets me forward without leaning over. My head got busy thinking about all this when I realized it wasn't obvious what ajustments to make. And there's always the possibility of moving the binding as well now that I think about it, so stick to a bootfitters observations for change suggustions to get where you want to go the fastest.
post #14 of 14
Jasonhawk54,

It sounds like you are making new discoveries all the time and you are on your way to a better understanding of boot alignment. Maybe check out the ask a boot fitter forum once in awhile and read what some pros have to say to help you round out your understanding of alignment parameters. Also, check out the link below to snowind.com and click on boot fitting for more info.

bud
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