Lets see here, Going down a mountain, on a glacier full of snow and ice, propelling yourself as fast as possible, right alongside more people than you can count, on a two wheeled bicycle !!! What could Possibly go wrong ???...lol...lol...DAMIEN
Here in Tennessee I've hit down hill speeds of 50 mph. A stopping distance on level ground at a certain speed will more than double going down long steep hills. The reverse is true going up steep hills. A stopping distance at a certain speed on level ground will be cut in half when going up a long steep hill.
The above statement is based on dry conditions on a paved surface. Factor in ice or wet conditions changes that for the worst.
I'm pretty sure those boys know there is no stopping, so brakes are useless.
That first video is hilarious, everyone crashing and so many more coming down. They're sliding their bikes in hope of not crash into the mess down the hill.