Wanted to share my experience with the Knobby Knife
http://www.knobbyknife.com/ a tool to help 'freshen up' worn tires by putting a sharp leading edge on the knobbies.
First, I would like to say that I got one a while back and it didn't really work, got frustrated with it and just put it away to collect dust. Last week I was talking to a riding buddy and the topic of tires came up. Hmmm, I remember I have this thing called a Knobby Knife! I knew mine didn't work (didn't get hot enough), so I called the company to see what they suggested or could do for me. This is a small family owned business and the next thing I know, a new one was in the mail, gratis. 2 days later, I'm cutting tires!
This is my first real attempt and I don't think I did too badly - didn't take long either. Going trail riding this weekend so I will see how well they do and hold up!
YES - it does cut some of the knobby off, but you gain the sharp biting edge.
Tire is a Michelin M12 - see my original post about the tire here
http://690enduro.createaforum.com/tires/120100x18-tire/?message=1539;PHPSESSID=c9f7a3debb81915c461c854fa46e2af3 (pictures are not great, sorry)
Rounded edge
First few attempts at cutting a sharp leading edge
100w soldering iron type tool with a sharp blade that gets hot enough to cut knobbies