I don't ride for pleasure if it's below 40 F. I'll commute down to 5 F, even though I start complaining around 12 F. But I've spent years amassing excellent winter gear At around 5 F my bike doesn't work very well, shifters and brakes are sluggish, and it's all just too much of a hassle.

Heat bothers me a lot more. I struggle above 80 and at 85 I'd rather not ride anywhere except straight to the beach. I just don't have many coping mechanisms for the heat.