Equipment: '09 CAAD9-5, full 105, ROL Race SL Wheels, Conti GP4000s tires.
Me: 6'0", 180, reasonably strong rider, stick arms, big legs.

In the last few rides I've been on I've been attacking some of the short steep hills around harder than I have previously...out of the saddle, on the hoods. I've been finding that I'm spinning the rear wheel on the downstroke and sometime on the upstroke when I'm concentrating on both. Now, it's been colder here in MN, close to colder than I've ever been riding in...I don't think I'm leaning over the bars any more than I usually would. Could I be seeing:

1) Less traction due to colder pavement/tires?
2) Unconsciously leaning farther over the bars when trying to go harder?
3) Anything else?

If I consciously lean back a little it doesn't slip but it's a position I've never felt myself be in before, hence why I don't think I'm leaning farther forward than usual.

Any thoughts?