You don't need traction, you need easy rolling. Harder tires = less rolling resistance. The reason you use those big inflated tires in the first place is to keep from sinking into the sand.

Of course, this is coming from a guy that doesn't have a set of beach wheels. I launch from my trailer every time, so take-it or leave-it <img src="http://www.catsailor.com/forums/images/graemlins/smirk.gif" alt="" />