Maybe it's just years of city living and riding for transportation, but I've never left any of my bikes unlocked. However, I've seen lots of people doing this on rando rides -- how do you know when it's OK? Only in a group? And if you carry a lock, how much of one? Enough cable length to handle both QR wheels without taking a wheel off? Smaller? Right now I'm carrying a cable that is (if what I'm locking to is in the right place), just long enough to do so, plus a small padlock. But I was also the only one I saw lock up on a recent populaire, and I see lots of people's photos from brevets with bikes just strewn everywhere. Do you just watch it from the window?