Seems like there are three approaches to locking up:
1) completely unlocked.
I'll do this on a charity ride when I'm surrounded by lots of unlocked bikes much nicer than mine. Aside from that I avoid this approach, partially because a neighbor of mine had a bad experience trusting small towns during his Northern Tier ride. (He published a journal of his ride, A Crossing by Brian Newhouse)
I was concerned when one poster to this forum advised going unlocked in major cities... this advice seemed very unwise to me:
"Re: Bike locks
« Reply #5 on: April 05, 2011, 01:48:36 pm » My touring has been in Europe and the USA. I'm not sure I took a lock on any of my tours. Its been a few years so I may have forgot what I carried. I recall visiting a museum for a day in Munich and leaving the bike outside in a visible area. Unlocked. Bags and bike were still there when I returned. "
2) lightweight cable lock.
This can be a nice compromise position... I had an eye-opening experience with this, though. One of my students (I'm a high school teacher) offered to show me a magic trick. He took my cable lock (as a bicycle commuter I park my bike in my classroom) and in less than a minute had it opened up.
"How did you learn how to do that?" I asked.
"YouTube." came the reply.
So I googled "bicycle combination locks" and the first item was an instructional video on how to crack the combinations. So if you go the combination lock way, be careful to get a more serious combination.
I was relieved when an old thread got reactivated today on the website to see another description of that same day in Munich that had concerned me.. it seems that the bike really wasn't unlocked, after all.
" Re: Bicycle Security
« Reply #4 on: August 09, 2004, 09:55:51 pm » Quote
Back in 1992 I toured loaded in Europe. One day I parked my fully loaded bike, with panniers, in front of a museum in Munich, Germany. I used my cable lock. I spent several hours inside. The bike and bags were just fine when I returned. "
3) maximum security.
This can include a Kryptonite style U-Lock and cable or a variety of hardened chain locks. This is the direction I've headed into over the years. While no lock will stop a determined thief, it can lead a thief to move on to the less secured bike on the next rack. My goal is to never be the "least secure/most expensive" bike in any situation.
Those of us who ride in cities are accustomed to these kinds of systems. If you'd like a humorous and informative look at how to secure a bike here's a short video worth watching.