Depends on how serious you want to be. For casual trail riding on frozen snomobile trails you can use sheet metal screws. To be competetive on the ice you need to use the Koldcutters or similar ice screw. They have a taller, sharper lip that makes a huge difference. To be really competitive you need a particular tire and usually pay soemone to put screws into them in a particular "secret" patern. Where I live there are one or two guys that make everyones competition tires. Not to discourage you but that is how it is (at least where I live). I have spent many evenings theorizing the flex of tires and making cool stud patterns - mine all worked like crap. They even have a trellebourg class here where you can run the tires that come pre-studded. Hope this helps. Cam.
