The real problem with the Subaru Outback's burning smell

I have experienced this symptom many times here in the White Mountains of NH (including yesterday). It occurs after I go up a long steep hill with snow tires, especially when there is some slippage on the way up, get out of the truck and smell burning rubber. It doesn’t happen in extremely cold conditions, but more when the temp. is in the high twenties and up.

I wonder if Stan has snow tires or some extra-soft all season tires.