SKI BOOTS – WHAT’S YOUR ANGLE?


Before I select a new ski boot I want to know the ramp angle of the ski/binding system of the skis I am skiing on.  The net ramp angle is the angle of the boot board in the base of the ski boot plus any ramp angle created by a difference in the height of the heel and toe plates of the binding. The reason net ramp angle is important is that elevating the heel of the foot in relation to the toes (positive ramp or drop) can have either a positive or negative effect on the function of the feet and legs, in particular, the outside foot and leg of a turn. A small amount of ramp angle can significantly stiffen the ankle torsionally and stiffen the foot in general in a way that enables maximal pronation by allowing the forward lean of the column that supports the centre of mass to increase slightly. But past a certain threshold too much net ramp angle can have the opposite effect. Through subjective experimentation in 1977-78, I arrived at approximately 3 degrees as what seemed to be the optimal net ramp angle.

To calculate net ramp angle I use a micrometer or caliper to measure the height of the toe and heel piece platforms of the bindings of my skis and the toe and heel ends of the boot board. First, I measure the height from the base of the ski to the top of the heel and toe plates of the ski bindings. The photo below shows how I measure the height of the heel and toe piece of the Look Nx Fluid binding. In this situation, the ski base to heel piece platform dimension is 5 mm higher than the ski base to toe piece platform dimension. I prefer to use degrees of ramp angle as opposed to what is called ‘drop’ in mm. Degrees are uniform across different foot size whereas drop is not. The ramp angle for the Look binding in the photo below calculated out at positive 1.5 degrees when set up for a 250-255 ski boot. However ramp angle will vary depending on the space between the heel and toe pieces because the vertical dimensions are fixed. Therefor, the ramp angle will increase as boots get smaller boot and decrease as a boot gets larger. So it is important to calculate the ramp angle with the binding set up for the correct boot.

Micrometer

 

The photo below compares the Look Nx Fluid binding above to a Look Racing Px4 binding. There is no difference between the ski base to binding platform heights of the heel and toe pieces of the Look Racing Px4. So the ramp angle is net zero degrees whereas the ramp angle of the Look Nx Fluid binding is positive 1.5 degrees when set up for a 250-255 ski boot.

Binding Ramp

Most people probably assume that there is some grand strategy behind binding design and ramp angle. But as far as I have been able to tell there, is no rhyme or reason for variations in heel and toe piece platform heights let alone any consistency. I prefer bindings with zero net ramp angle for several reasons. It eliminates a variable that compounds boot board ramp angle. And it eliminates the problem of binding ramp angle changing with changes in the spacing between the heel and toe pieces.

How critical is net ramp angle? I believe the tolerance is very narrow. A ramp angle of 3 degrees may have a very positive effect whereas a net ramp of 4 degrees may have a negative effect. Too great a net ramp angle can have the effect of plantarflexing (ergo – extending) the ankle. Extending the ankle effectively lengthens the chain of muscles in the back of the leg that exerts what I call the plantar-pelvic pull. The sheet-like ligament that underlies the arch of the foot and runs from the toes to the heel is an extension of the Achilles tendon. The chain of muscles in the back of the leg (soleus-gastrocnemius-hamstring) is the chain of muscles in walking and running that act as the centre of mass moves forward to stiffen the foot in preparation for propulsion. Effectively lengthening the chain of muscles in the back of the leg decreases their contractive force and can significantly reduce the stiffening of the ankle and foot required for good balance and control of the outside ski and especially the amount of pressure that can be exerted on the ball of the foot as it pronates.

As far as I have been able to ascertain, the concept of net ramp angle doesn’t appear to be a consideration in ski equipment setup. Yet, I believe that net ramp angle in combination with correct cuff cant and forward lean can literally make or break a skier and especially a racer.  In watching video of World Cup racers, especially females, the typical stance and movement patterns suggest that the majority have excessive net ramp angle. If you want to ski like Ligety and Shiffrin, you need to be able to extend the way they do. You will not able to do this so as to engage the external forces to drive the outside ski into a turn without the correct net ramp angle and cuff cant and forward lean.

In my next post I will describe what I look for in selecting a ski boot.

 

 

2 comments

  1. I can’t imagine that 1 degree of extra ramp angle would have that critical an effect…3 versus 4 degrees? Excessive enforced forward lean caused by the ramp angle, would, in boots with a lot of resistance to hinging of the cuff, simply pitch you forward in your ‘neutral’ boot position. Any further forward motion involving hinging of the cuff would put your CoM further forward again, and this would facilitate forward motion of the CoP to the metatarsal head. In boots with a freer cuff hinge, the skier might well plantarflex as you describe, to remain more vertical. It seems to me that the dorsiflexion-pronation motion needs to be a 2-way street…you need to get quickly out of that pronated position at the end of a turn, and if you’re tilted forward too far then that might interfere with getting out of the pronated position and off that edge at the end of the turn.

    1. Bear with me. There are still many posts to go before all the pieces will in place. You supinate (unpronate) the outside foot of a turn the same way you do in gait. You unload it. How? by moving to the inside (new) ski in a transition phase and extending the limb. This releases the old outside ski from contact with the snow. The criticality of ramp angle is in the context of balance on one foot not on two feet. Is ramp angle that critical? In my considerable experience….. absolutely. It is nothing short of tragic the way the promising career of a young ski racer can literally disintegrate after an equipment change because no one seems to be the least bit concerned about details like net ramp angle. They can just write it off to psychological issues and bring in a new racer. When my spouse got new boots and skis her net ramp angle was 7.5 degrees. Until I reduced it to a little other 3 degrees she could not extend or balance on her outside ski.

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