I live in Baltimore, a city that still struggles with crime. As such, I take the security of my belongings seriously, and no place is this more evident than with the thing I most often leave in public: my bike.
In the past, and in safer cities, I have used steel cable locks without any problems. However, while locking my bike up around Baltimore I would frequently see the cut remains of thick steel cable locks. My dismay was reinforced when I saw a video of the time (mere seconds) it took to cut through even a thick steel cable lock with a pair of bolt cutters. Disconcerted, I asked my bike-savvy friends for a better solution. The universal answer was a Kryptonite U-lock coupled with a steel cable used to lock both your front and rear wheel to the bike frame and an immovable object.
I have a mixed history with Kryptonite. Eight years ago I owned and used an early version of their U-lock. Its size, weight, and ungainliness left much to be desired. In addition the model I owned had an embarrassing reputation for being picked by nothing more than a simple Bic pen. So I was wary when everybody and anybody with any knowledge about urban bike riding told me to use a Kryptonite lock.
After a few months with the new U-lock it is clear that eight years of substantial design changes have made a difference. Not only have they fixed almost every issue I had with my old U-lock, but they have made it smaller, lighter, and more secure.
Favored by bike couriers, the U-Lock is designed to couple the front wheel to the frame of the bike while locking to an external post, stop sign, or other immovable object. What Kryptonite has done to make this more usable is by shrinking the width and length of the U-lock so that it fits snugly into most back pockets (while the shorter length means it doesn’t fall out while riding). This subtle change makes it far easier to carry the lock thereby avoiding the need for a bag, or even for attaching it to the frame of the bike through a plastic connector (which are, at best, unreliable and prone to breaking).
In shrinking the lock for portability Kryptonite has also made it more difficult for bike thieves to steal the bike by preventing them from fitting a car jack between the lock and the steel bar (the main technique used to bust larger U-locks).
The one downside to Krytponite’s U-lock will always be its significant heft. The lock is predominantly made up of a solid chunk of hardened steel, and as such it weighs a considerable amount. But the knowledge that my bike is safer is much less of a burden than the few ounces of steel.
[For those interested in something even more secure and don't mind the extra heft, Kryptonite makes an overbuilt U-lock that is a bit more expensive available at Amazon.--OH]