You'll probably see me decked out head to toe in arm warmers, toe warmers, leg warmers and other "too-warm" clothing. But keep in mind:

1) I start at sunrise (6:30AMish), and it's usually 40-50F, even when it gets up to 70F by noon.

2) When you see me at 11AM or noon, I've been riding for 5-6 hours. When you're on the bike that long, the last thing you want is to be underdressed and shivering - that can get dangerous. On rides <2hrs, I can just suffer it out no problem, but at 5-6 hours, you're talking dangerous chill, especially when you're wet.

3) Lots of cyclists do the local climbs. The temp difference at the top and bottom can be over 30 degrees, not including weather effects. From experience - it majorly sucks to be dressed for 75F, then go bombing through a valley where there's no sun, a fiece wind, and the temps have dropped to 40s.

I've learned the hard way from having to abort long rides several times because I was too cold that I really have to err on the warmer side. Particularly for the longer rides where I'm out for awhile.