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- Sep 14, 2016
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- 109
These are somewhat arbitrary, but some of the definitions above do not correspond to the terminology as I've generally seen it used. Here are, I believe, some more precise definitions:
DELTA: Heel height - toe height, measured at the contact points with the boot (heel at most rearward end of contact area, toe at most forward end of contact area); generally given in mm. The advantage of using delta is it allows a single specification for each binding, since this doesn't vary with BSL (that's why the mfrs. use delta instead of ramp angle). It's called delta because the greek letter ∆ (delta) is used in science and engineering to specify a difference. E.g, ∆E means the difference energy between two states.
Elite racers will sometimes adjust their deltas depending on the event, but most good recreational skiers will want to find a single delta at which their fore-aft balance is optimized in all conditions (this is boot-specific, but is essentially independent of what ski you are using). @bud heishman can confirm this, but most good recreational skiers need to have their delta right to within 1 mm to have their fore-aft balance dialed in. Once you've found it, ideally you want to use it on all your skis. But what happens when you buy new boots? Well suppose your optimum delta was 4 mm in the old boots, and your bindings were all likewise conveniently 4 mm. But then you buy new boots in which you need a delta of 2 mm to be balanced. In that case, you don't want to shim all your skis; instead you just gas-pedal the new boots by 2 mm.
[I'm very sensitive to fore-aft balance because mine's currently messed up -- my alignment specialist and I have concluded I can't achieve it it my current boots, so I have to get new ones!]
RAMP ANGLE: The angle of the boot's outer sole that results from the delta (i.e., I've generally seen it used to refer to the external angle, not the internal bootboard angle, which is referred to as "zeppa"). Ramp angle = arcsin(d/x), where d is the delta and x is the distance between where the heelpiece and toepiece contact the bottom of the boot (and is thus less than the BSL, though as an approximation you could use the BSL). As a general rule, you get 1 degree of ramp angle for every 5 mm of delta (so the pic above showing four degrees of ramp angle would actually require 20 mm of delta!). WC skiers can sense changes in their delta of 0.5 mm, which is only 0.1 degrees! Recreational skiers that are sensitive to their fore-aft balance can sense 1 mm, which is only 0.2 degrees.
HOWEVER: The phrase "ramp angle" really can refer to the angle of anything made with a pitch, so there's nothing technically wrong with using "ramp angle" to refer to bootboard angle. You just have to be clear in how you define your terms.
ZEPPA: The internal angle of the bootboard. Because that's the key specification for a bootboard, some actually refer to the bootboard itself as "the zeppa."
DELTA: Heel height - toe height, measured at the contact points with the boot (heel at most rearward end of contact area, toe at most forward end of contact area); generally given in mm. The advantage of using delta is it allows a single specification for each binding, since this doesn't vary with BSL (that's why the mfrs. use delta instead of ramp angle). It's called delta because the greek letter ∆ (delta) is used in science and engineering to specify a difference. E.g, ∆E means the difference energy between two states.
Elite racers will sometimes adjust their deltas depending on the event, but most good recreational skiers will want to find a single delta at which their fore-aft balance is optimized in all conditions (this is boot-specific, but is essentially independent of what ski you are using). @bud heishman can confirm this, but most good recreational skiers need to have their delta right to within 1 mm to have their fore-aft balance dialed in. Once you've found it, ideally you want to use it on all your skis. But what happens when you buy new boots? Well suppose your optimum delta was 4 mm in the old boots, and your bindings were all likewise conveniently 4 mm. But then you buy new boots in which you need a delta of 2 mm to be balanced. In that case, you don't want to shim all your skis; instead you just gas-pedal the new boots by 2 mm.
[I'm very sensitive to fore-aft balance because mine's currently messed up -- my alignment specialist and I have concluded I can't achieve it it my current boots, so I have to get new ones!]
RAMP ANGLE: The angle of the boot's outer sole that results from the delta (i.e., I've generally seen it used to refer to the external angle, not the internal bootboard angle, which is referred to as "zeppa"). Ramp angle = arcsin(d/x), where d is the delta and x is the distance between where the heelpiece and toepiece contact the bottom of the boot (and is thus less than the BSL, though as an approximation you could use the BSL). As a general rule, you get 1 degree of ramp angle for every 5 mm of delta (so the pic above showing four degrees of ramp angle would actually require 20 mm of delta!). WC skiers can sense changes in their delta of 0.5 mm, which is only 0.1 degrees! Recreational skiers that are sensitive to their fore-aft balance can sense 1 mm, which is only 0.2 degrees.
HOWEVER: The phrase "ramp angle" really can refer to the angle of anything made with a pitch, so there's nothing technically wrong with using "ramp angle" to refer to bootboard angle. You just have to be clear in how you define your terms.
ZEPPA: The internal angle of the bootboard. Because that's the key specification for a bootboard, some actually refer to the bootboard itself as "the zeppa."
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