Long Thong - I don't think designing a spring that covers an adequate range of loadings is at all an issue because;
a) The spring in even the simplest conceivable release mechanisms only need to cover a relatively small range in forces. Look at the DIN chart
on Peter Keelty's site. As an example, for a fixed boot size and skier level, going from a 92 lb tiny adult to a 210+ lb "big guy" only changes the twisting release torque from 31 to 67 newton-meters. This is only a factor of two, and is well within the capabilities of simple springs. In other words, this is easy to achieve without the turns of the spring touching each other or the force dropping under the minimum necessary preload value, etc.
b) In addition, in slightly more complicated mechanisms (eg, a roller on a cartiod shaped cam with the rest position being "in the notch" ), the required excursion of the spring can be made even smaller than that needed in a simple design, thereby placing even fewer constraints on the design of the spring.
Personally, how I handle this issue is that as long as my DIN setting is at least one unit to the "inside" of the min and max settings, I will use that binding.
However, to make sure the bindings that I am using on a particular day will release when needed, won't pre-release, haven't been damaged in some other way (ie, fall apart, come off the ski, etc.), just about every day when I first click into my skis, I will immediately force an intentional twist and forward release on each ski. If I can't do this, or if it feels easy/hard/odd in any way, I try it again. If it still doesn't feel good, I then take them off and look things over, or at worst, take them into the shop. Thusfar, the only things that this test has ever detected is some caked snow on my boot and a couple of loose mounting screws over the years. By seeing that this few second test even detects simple problems like these, I am reasonably confident that there are no other problems and that my bindings will likely be working when I need them.
Tom / PM
PS - LongThong - You ought to check in at www.dcski.com
for discussions that are local (mid-Atlantic) interest not likely to be covered on Epic. Often you can find out about deals, conditions, etc., especially at WT, Liberty and Roundtop.[ March 20, 2003, 07:28 AM: Message edited by: PhysicsMan ]