Originally Posted by mogulmuncher
45 mph is fairly quick for a 167 cm ski. On a really hard packed surface, the vibrations that you'll get at that speed won't dampen as quickly as with a longer & stiffer ski, and the chattering can result in an unexpected binding release. This effect gets worse if you happen to get onto the inside ski -- the shocks to the relatively unweighted outside ski will often trigger a release.
The observer you mentioned might not have had a suitably trained eye to pick up a technical factor that could have influenced the crash. These things happen on occasion even to very advanced skiers, but you need to know what to look for.
Plenty of skis can handle the vibration of 45 mph just fine. Here's the problem with going 45 mph on a 13-m sidecut ski.
Let's say you are making a hard turn at that speed. Let's say you are pulling 2 gs. Let's simplify it a bit for the sake of this example and say you are pulling off a 2 g turn on a horizontal bit of hill.
The acceleration in going around a corner is equal to V^2/R. Setting this equal to 2 g, we get R = V^2/(2g)
45 mph is 20.11 m/s. g is 9.81 m/s, so the radius of that 2g turn at 40 mph is 20.63 m. We can see right away that the ski is skidding a bit.
Now look at the horizontal force needed to push you around the turn F=ma = mV^2/R.
Look at the upwards needed to keep you from going through the ground F=mg
The angle of the resultant force is given by tan (t) = V^2/(Rg)
or t = 63.4 degrees.
You have to angle your skis at 63.4 degrees in order to resist that force.
Now look at the turn your ski would like to carve if it were to lock into its edge.
R = Rsidecut * Cosine(t) = 5.81 m.
If your skiing along at 45 mph rocking a 2g 22-m radius turn on your 13-m sidecut skis, and they suddenly decide they are going to carve the turn they were designed for, you will be fortunate if your binding lets go, otherwise you will get a very sudden sideways force of 7 times your weight pushing on your fib/tib.