I ran into this on my local MTB Forum. Apparently, this is relatively common place "up here in these parts". Homemade 'tire-studding' to ride in icy or snowy conditions. Gives more traction, grip, etc. Anyone else heard of this or completed it on their own? Here is the link to build your own: http://www.morcmtb.org/wiki/index.php/Tire_studding
This is not me, by the way, just a pic I found on the web. I'm debating on doing it, though.