NEVER put a u-lock around BOTH the rear wheel and the seat tube. Never.

1. Dumb crooks use the bike's frame as a lever to attempt to break the u-lock. This actually can work with a $5 u-lock and a thirty pound frame. But, with a good u-lock, it turns the seat tube into a pretzel.

2. Use the smallest u-lock that fits around the rear wheel and a locking post. A compact u-lock does not leave enough empty space to insert effective prying and leverage tools. If a compact u-lock is locked to the rear wheel, just behind the seat tube, it is IMPOSSIBLE to separate the frame from the wheel. If you lock ONLY the frame, you are making a "gift" out of your rear wheels.