If you are wearing shorts under and just need something light, I found that several athletic companies are making "workout" 3/4 tights and they work great for me and pack easy into a jersey pocket if it warms up. Dicks sporting goods sells their own brand plus Nike and other companies. Because they tend to be thinner, I also bought full length tights for those days that are cool but not cold enough for thicker cycling tights.
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Keep the chain tight!