I think my front ski helped quite a lot in the snow.. two different times I remember all of a sudden my rear wheel would sink pretty deep, when the front of the bike stayed on top of the snow..
[youtube]mAZ6xWOcP9M[/youtube]
Well so far I have only tried the SlipNot's using a tire that has a very flat/smooth profile.. and I noticed very little rear wheel spin-out.. I want to try and find a narrow tire with some nice nobbies.. The SlipNot's need 1/4" space between tire and frame..