Rear drive 5K

[Sperry, Peter A -Syntegra MN]

Here in Minneapolis it's been snowing pretty good the last few days, and
it's given me a chance to play in the snow in my Audi.  The problem is this:
when going around a corner, I make the corner (barely) and then the tail end
spins out.  It feels like either my rear tires are bald and the
accelleration in the turn causes them to plane out on top of the snow.
However, the tires are fine, they are not snow tires, but M&S rated.  They
are the ones that were on it when I bought it, and are made by Duralon
(cheapies I'm sure).  Are my tires the problem?

Peter
'88 5KSQ
'90 90Q (on they way)