I know that compared to a lot of places, the San Francisco Bay Area does not really have winter. But some mornings, before dawn, riding to work on the waterfront, the wind coming off the saltwater takes the temperature down below freezing. On those mornings, uncovered ears lead to dizzy spells, it gets so cold.
Before I made these earwarmers, everything else I tried interfered with how my helmet fit on my head--balaclavas, scarves, headbands--these fit right on the helmet's straps, below where the helmet hugs my head, so they pop on easily for the coldest mornings, and pop off when they're not needed, without any helmet adjustments required!
And they're so warm!
Details on my Ravelry project page; the pattern's available for free in MenKnit issue one. And be sure to see the comments on the Ravelry pattern page for this pattern for an explanation of a possible typos in the pattern as published.