I run chains all winter long, so for plowing, I don't think the condition
of
the rear tires matters much. In fact I keep the chains on a pair of wheels
with old, hard, slippery tires, and save the wheels with the sticky new
tires for summer.
Putting new tires on the front made a huge difference in steering though.
In snow, the tractor used to sort of go in the general direction I turned
the wheels, if I were thinking nice positive thoughts at that moment. Now
it actually goes where I point it most of the time. Funny how that works.
(Thanks for the good tires, Jim.)