Calculating Boot Board Ramp Angle
(From the editor: This from the David MacPhail discussions and thanks to RicB for the Word document! The original was written by David.)
To use math to calculate amount of ramp angle for your body height and foot size you need two sides of a right angle triangle; the base A-B and the vertical aspect of the base A-C.
The base A-B relates to the plane of the ski surface as the reference for net ramp angle. It is the dimension between 2 easily located landmarks on the foot; 1) the prominent bump on the instep where the 1st metatarsal (ray of the big toe) connects to the midfoot (i.e. the ‘navicular’) and, 2) center of the head of the 1st metatarsalAttachment 1080
To find point A (navicular) run your finger or thumb towards your big toe from just in front of your ankle. You should feel a very distinct bump. Try and find the center as best you can and then mark it with a fine felt pen. CoM is actually more rearward but the navicular is the most reliable landmark.
To find point B (head of the 1st metatarsal) run your finger/thumb down to the ball of the foot. Flex your big toe up and down so you can feel the joint. Try and find the center of the head of the 1st MT just behind the joint then mark the center with a fine tip felt pen.
Stand on a sheet of paper and use a right angle set square to transfer both points to the paper. Measure A-B. Take 70% of the resulting figure to allow for a safety margin to ensure the CoM does not pass the ball of the foot.
To find the dimension A-C stand erect in your normal posture. Measure the distance from the ground to your belly button. Take 95% of the resulting figure to allow for CoM being a bit below the belly button and to allow for some ankle, knee, and hip flexion. A-C is the reference for the normal position of CoM.
Point B (red triangle) is the reference point that the foot rotates about to move CoM forward. Point D is where ramp angle should move CoM to. This usually gives a ramp angle of 3 degrees using computer modeling. I am estimating the reductions. So if the math doesn’t give 3 degrees some adjustments may be required.
(Editor: If anyone has any idea about how to add points and lines to this diagram, please let me know!)