Originally Posted by kbarch

Legs can tolerate a wider range. I never had or saw any advantage in leg/knee warmers until this past spring. They're good for longer rides where it starts out cold but warms up into the 60's +. If it's just chilly (upper 50's, low 60's), usually riding will warm them up sufficiently, but if it's cold, the knees just don't get comfortable and the legs, while they may not feel cold, just don't loosen up. Aside from that, if it doesn't look to get out of the 50's during the ride, I'll put on tights.

Arm warmers, similar concept - most useful for rides with a cold/chilly start when one expects it to warm up eventually, but not in much less than an hour. However, for the upper body, wind is more of a concern, and arm warmers are not much help in that respect. A highly-compressible windbreaker - one that can be easily packed into a side jersey pocket - is much more useful for cool days, and a vest is good if it's generally mild, but with wind chills likely during descents.