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#1
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Technical Information Needed
Tuesday, November 16, 2004
I’m looking for some technical information on skis/bindings. I have been skiing since 1968 and enjoy a run down any trail in any conditions. My problem this year is I’ve lost some weight, about 30 lbs, and want to properly set my bindings from last year’s “heavy” values. Skied Killington last week and the first run down West Glade through the bumps was great, as a precaution I took one number off the spring tension and had no problems. But, did I go far enough? Also, does anyone ever compensate for the added weight sometimes carried - ski coat, back pack, water, all add weight – should this be factored into the total skier weight? As background info, I’m a degreed engineer and really understand mechanical systems such as a binding – very concerned when I see so called “Ski Technicians” doing a binding check which from what I observe is nothing more than verifying that the binding DIN value matches a number on a chart for a skiers ability and height/weight combination. Where do I find this chart? Has anyone experimented with different base/side wall edge angles on Volkl P50’s? |
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#2
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johnkuc wrote:
Tuesday, November 16, 2004 I’m looking for some technical information on skis/bindings. I have been skiing since 1968 and enjoy a run down any trail in any conditions. My problem this year is I’ve lost some weight, about 30 lbs, and want to properly set my bindings from last year’s “heavy” values. Skied Killington last week and the first run down West Glade through the bumps was great, as a precaution I took one number off the spring tension and had no problems. But, did I go far enough? Also, does anyone ever compensate for the added weight sometimes carried - ski coat, back pack, water, all add weight – should this be factored into the total skier weight? As background info, I’m a degreed engineer and really understand mechanical systems such as a binding – very concerned when I see so called “Ski Technicians” doing a binding check which from what I observe is nothing more than verifying that the binding DIN value matches a number on a chart for a skiers ability and height/weight combination. Where do I find this chart? Has anyone experimented with different base/side wall edge angles on Volkl P50’s? DIN http://www.terrymorse.com/ski/din.html The accuracy of the binding scales is such that you really can't do any better than setting to chart based on a range - that's why the torque release value testing is important. In Europe they sometimes measure the diameter of the tibia head and set to this measure - I've never seen it done in America. No one adjusts binding settings based on added clothes weight IME. If you're going to experiment with edge/base angles be sure to sneak up on it - it's hard to reduce edge angle and it'll chew up alot of base to grind out a base bevel. I'd start with a flat base and a one degree acute edge; if you feel like you're hooking, try a 2 deg edge, 1 deg base bevel (about what Volkl recommends, IIRC.) (FWIW, I ski my Volkls at flat base, 2+deg edge.) |
#3
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"johnkuc" wrote in message
... I'm looking for some technical information on skis/bindings.... There are, I think, a number of discussions on this topic here (and elsewhere). Weight isn't the issue, it's just an indirect way of measuring what you really care about, which is bone (and, to some extent, ligament) strength. A DIN number is associated with a particular torque that's required in order for the binding to release. When they use fancy equipment to test bindings, all they're doing is checking that the DIN number marked on the little window on the binding corresponds to the torque that it's supposed to. They're not checking what the DIN setting "should" be. There's not a good way to do that, short of torquing your leg until it breaks. The variables typically used in the charts a - Height and weight. Between them, these are supposed to give an approximaton of how strong your bones are. Of course, this is highly imperfect, as they don't distinguish between a 6' 200 lb guy who's built like a linebacker and a 6' 200 lb guy who's just fat. As noted above, there are charts that use tibia-head diameter instead: I have some that came with Marker bindings, or at least used to. Whether that's a better measurement, I can't say. - Boot sole length. This is necessary to convert between torque at the toe (where the binding is) and torque at the ankle (where the bone gets twisted). Longer boot sole - lower setting, because, compared to a shorter sole, a relatively lower torque at the toe produces the same torque to the bone. - "Skier Type." This is really in there because bindings are not perfect, and it's necessary to balance one potential problem (not releasing when they should) against the other (releasing when they should not). The former is the by far the greater danger for slow-skiing beginners, while for fast-skiing, chute-loving experts, the latter becomes more important. This is the case for several reasons: (i) when you're going slowly, "slow twisting falls" are more likely: falls in which the force builds up gradually, while the endangered leg is weighted, producing lots of boot-ski friction; (ii) when you're going fast, very short duration shocks, which don't hurt you, can easily knock your bindings off; (iii) when you're dropping into an icy rock-lined chute, the downside of a premature release may be a lot worse than a mere broken leg; (iv) same thing when you're flying along at 50 mph. - Age. Bones get brittle in middle age. So, really, gaining and losing weight shouldn't affect the proper DIN setting (unless you're gaining and losing weight in your bones). Weight you're carrying shouldn't affect anything. Sure, both of these will increase the torque that gets applied at your boot ... but they don't affect the torque at which the binding should release, which remains: just enough before you break something to give an appropriate margin for error. One final thought: it seems that the history of binding development has been most oriented to avoiding spiral fractures. That goal has been pretty nearly accomplished: fractured legs are much, much rarer than they were twenty years ago. The bigger danger now is to knee ligaments. Nobody has quite developed a binding that's really effective at protecting knees. Among top racers, the mean time between knee injuries is absurd: something like three years, at most. |
#4
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sjjohnston wrote:
CLIP Nobody has quite developed a binding that's really effective at protecting knees. I think the old Nava binding/boot combination of 20 years ago may have effectively prevented knee injuries - it's problem was it also effectively prevented skiing. |
#5
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johnkuc wrote:
... I’m a degreed engineer and really understand mechanical systems such as a binding – very concerned when I see so called “Ski Technicians” doing a binding check which from what I observe is nothing more than verifying that the binding DIN value matches a number on a chart for a skiers ability and height/weight combination. A proper release check is more than simply verifying that the DIN indicator is set to the right number. It involves actually measuring the torque required to release the boot from the binding. For me it's 58 newton-meters at the toe and 229 newton-meters for the heel. The modern machines that do this measurement are actually quite sophisticated and relatively idiot-proof. I'd bet you'd be interested in the process - ask the shop if you can watch. Now you don't usually see this testing at the rental counter because they don't have time to do it for every rental at the point of purchase. Presumably, they've already done the torque test at a non-busy time and can just set the indicator. Anyway, the smart move is to have your bindings tested at the beginning of every season, just as you have the brakes on your car inspected at periodic intervals. A release check usually costs $15 to $20, and is money well spent, if you consider the alternative. Has anyone experimented with different base/side wall edge angles on Volkl P50’s? I bought my P50s from a racer who had the edges set to zero bottom / two degrees side. I haven't changed it and it seems to work well. Maybe a bit grabby, but I like 'em grabby. IIRC, Volkl recommends 1 deg. bottom / 2 deg. side. -- // Walt // // There is no Volkl Conspiracy |
#6
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"lal_truckee" wrote in message ... sjjohnston wrote: CLIP Nobody has quite developed a binding that's really effective at protecting knees. I think the old Nava binding/boot combination of 20 years ago may have effectively prevented knee injuries - it's problem was it also effectively prevented skiing. Ain't that the truth. then there was the turntable heel, Talk about a pre-release bandit. |
#7
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"Walt" wrote in message news:k8umd.450 // Walt // // There is no Volkl Conspiracy sure there is . IIRC, Volkl recommends 1 deg. bottom / 2 deg. side. |
#8
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lal_truckee wrote:
DIN http://www.terrymorse.com/ski/din.html Here's another chart: http://home.online.no/~stigbye/skiing/equipment/bindings/DIN-setting-1_step-1.html or http://tinyurl.com/5djna I went the other direction a few years ago. Adding less than ten pounds bumped me from a DIN of 7 to one of 8.5 using the chart. Being an engineer, I just wish they'd give me a formula instead of the chart. Of course, if I wasn't quite so lazy, maybe I could reverse-engineer the equation from the chart. My current skis/bindings are unlikely to see the snow again, as they're due to be retired. I'll be renting on my next trip. |
#9
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Richard M wrote:
lal_truckee wrote: DIN http://www.terrymorse.com/ski/din.html Here's another chart: http://home.online.no/~stigbye/skiin...setting-1_step -1.html or http://tinyurl.com/5djna I went the other direction a few years ago. Adding less than ten pounds bumped me from a DIN of 7 to one of 8.5 using the chart. Being an engineer, I just wish they'd give me a formula instead of the chart. Of course, if I wasn't quite so lazy, maybe I could reverse-engineer the equation from the chart. My current skis/bindings are unlikely to see the snow again, as they're due to be retired. I'll be renting on my next trip. There's always the racers method, wind them up until the don't come off in the start gate -- Chris *:-) Downhill Good, Uphill BAD! www.suffolkvikings.org.uk |
#10
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