Tire testing at different temperatures
I've always been a little suspect of the 7C switchover temperature that everyone cites. Coming from the tire companies, it could be a marketing ploy.
Well someone actually tested it. This guy shows that the 7C temperature switchover applies to "summer" tires. " The "All season" tire he tested worked down to 2C on wet pavement. Another interesting point was that on dry pavement the summer tire worked best down to 2C.
While this is one test at certain conditions and only on specific types of tires, it does cause one to think about the 7C temperature swichover that everyone references.