Racesx, it's because we do alot more than just use the track dyno to make up our kits. The kits are initially developed on the track dyno and then field tested by a group of riders ranging from 150 lbs to 240 lbs (Myself, my father, or anyone else who is in our group rides so we know what adjustments are needed for different weight riders.) Generally we can go from our track dyno and I can jump on the sled out on the snow and be within 100 rpm of optimum rpm, but it all depends on the snow and weather conditions (I'm 150 lbs). It all comes down to a ton of testing and 5 years of track dyno experience to know what is going to work and what's not going to work out in the snow. Generally we can get away with something as simple as a secondary spring adjustment to go from a lighter rider to a heavier one or vice versa. Traction is also a big factor. If your sled is studded we can make the kit more aggressive because of the increased traction.
Allen