Are you locking your bike? If so, please check with your lock's manufacturer for how to lock up correctly. Here, I present bike locking don'ts. I call them the Bad, the Sad, and the Ugly.
In Picture One, the Bad, you see a strong, sturdy U-lock securing the front wheel of a bicycle. What you can't see is the front wheel is held only by a quick release. With a simple yank of the skewer lever, an opportunist can walk away with most of this bike.
Picture Two shows a case where the hypothetical opportunist described above was, in fact, the real deal.
Picture Three, the Sad, shows a cable lock securing the twisted wreckage of a water bottle cage. The rest of the bike is nowhere to be seen.
In Picture Four, the Ugly, a sturdy U-lock secures the frame to a good, strong bike rack. The wheels, seat post, and seat are missing. Using exposed street furniture for long-term bike parking can lead to the unintended parting out of your bicycle.
There are some basic principles here: It's always a good idea to lock the frame. It's a better idea to lock the wheels and the frame. All other things being equal (not that they ever are), heavier locks are harder to defeat. However, even the best locks can be defeated by faulty locking technique.
(A version of this article appeared in the April-May 2010 issue of The Chainguard, a newsletter of the San Diego County Bicycle Coalition, www.sdcbc.org).