Mark asks:

>Is there any risk in putting my brand new spare on when the other tires >have about 10K miles on them?

It hard to to tell how much wear you have in 10,000 miles, since that
is tire dependent.

The first thing I would do is measure the tread on the spare and compare
it to the other four. If there was a measurable difference, I'd take
the spare down to a real tire shop and have them shave it to the
same depth as the others. 

You'd lose a bit of mileage from the spare, but you would get it
into rotation and would not be worrying about your viscous coupling...

Tom F.