Bought the jacket hoping to use it for both mountain and road riding. I usually wear a medium but my chest is a little bigger than most men my size. Knowing I mountain bike 80% of the time I ordered a bit larger jacket for movement. Works great off road. But on the road it is a little loose in the wind, a medium would be great for me in this situation. Great jacket but if you ride both on and off road you may need two different sizes. Love it off road!