I can second that.... lots of weight on your back requires *extreme* care..... I did a rather long skid on the top of my head, I'm pretty sure, from having too much stuff in my messenger bag.... I hit a tiny pothole in the dark and the weight of my messenger bag came up over my head and carried me right over the handlebars. The helmet certainly saved my life that day- the shop guy looked at it when I came in to replace it and looked again at me (I was basically fine - somehow I escaped with just a tiny raspberry on my elbow) and said usually when someone comes in with a helmet like that they don't look too good.... I haven't stopped using the messenger bag, but I certainly take a lot of care when I've loaded it up and I always make sure that it's really well secured with the chest/stabilizer strap to keep the weight as close and low as possible on my back