Not if you are old and fat like me. I'll unzip most of the way if I'm riding alone and it's really hot. I zip up at least 50% if I'm stopping at a store or riding with others. You have to be considerate of others. Nobody wants to see pasty white blubber. Young slim folks, go for it! And no bibs w/o a shirt of some sort. Believe it or not, I've actually seen this.
