Some of us just sweat. I sweat when I eat. I sweat when I walk. I sweat when I ride. My metabolism runs fast and I sweat.

Although it's not as cold here in winter, it can get into the 30s and 40s, and I have a similar problem. When it's cold and on rides with extended climbs, I'm just soaking, even if I strip off most of my layers. Then, I freeze my butt off on the extended descent. My secret has been to pack a dry base layer in my jersey pocket (in a plastic bag) so I can put a dry layer next to my skin for the descent.