A few years ago I could comfortably ride in temps as low as -10 Celsius (14 Fahrenheit), but now I don't ride when it is colder than about -7 C or 25 F. There used to be a saying that "if your hands or feet are cold, put on a hat." I have a winter liner in my helmet and a silk balaclava . I sometimes have silk under merino long johns under cycling pants. I usually have a silk longsleeve tee under a merino Tee..my other layers might be a turtleneck and either a sweater o fleece pullover, it varies. I have lobster gloves or ski gloves; a yellow wind breaker, and I have thick socks.. If i'm too warm I take something off. It might be wise to carry something like a down jacket in a handlebar or saddle bag so when you stop, you don't lose heat and get cold.