This timely article popped up on CNN this morning;  Best Bike Locks

These are my security choices. My first tour of the modern age, 2008, riding from Crater Lake, Oregon to near San Luis Obispo, California, I took a 3 pound U lock and never used it even once. On future tours I took the ⅛ inch cable and $5 combination lock pictured, weighing in at 4.8 oz. A few years ago I added a 10.7 oz aluminum Palmy U lock. My plan is to take the Palmy and pictured cable to Europe in a few weeks. At any one time there will be three to five riders with various locking systems. We tend to lock all the bikes together in a “Gordian Knot” of steel, cable and in my case aluminum. 

My thought but never acted on was entering a city that might require greater security, would be to buy a cheap steel U lock at a Walmart or the like on the city outskirts and give it away when leaving.

The steel U lock pictured is a Kryptonite Mini at 2 lb 2 oz. I use it in part of my home town of Portland, OR where more security seems to be needed. Never taken it on tour.