I've carried a guitar in a gigbag backpack on my bike many times, and while it works, the downside is that the neck of the guitar sits directly behind your head. This tends to make you lower your head, impairing your forward vision a bit, and it can be a little uncomfortable if you're wearing a helmet. Not a big deal for a short trip or if your riding position is bolt upright, but I was never tempted to extend my route on the days I carried it. I was able to fit a binder into the external pocket of the gigbag.