I just posted this on another thread.

Tire sizes are very limited for studs. If you have a tire where studs aren't available check out this site. They are easy to make.

I have been making them for years before I came accross this site. Use "self drilling sheet metal screws". They are hardened and last a long time.

http://www.ecmtb.com/howto/stud.shtml

Gary D.