In winter the sun sits low all day. If you ride on a fine day, you can spend hours looking straight into it, and in the bends you barely see where the road goes.
Flip the sun visor down while it dazzles and up again in the shade. And remember that the spots where you see nothing are often the slipperiest. Where the sun never reaches, the surface can still be frozen in the afternoon.
In winter, plan shorter stages. Dusk comes early, and the cold comes with it.