I figure anyone who leaves a $900 bike unattended without some kind of lock is crazy. I carry a cable and fair quality padlock. It would discourage the casual thief. Between my extra 10 lbs of lard and all the crap I've loaded on my road bike: Armadillo tires, mtn bike cluster and derailleur, carrier with my junk bag, mirror, bell, air pump, underseat tool bag, bottle(s?) of Gatoraid, I don't think the lock is that much more weight.