Bike commuting means bike theft. You need a good lock. We used a hammer, bolt cutters, and a Dremel rotary saw on these (way beyond what most thieves would deploy) to see how they'd hold up.
1. Kryptonite New York Legend 1590
The 15-mm-thick hardened-steel links on this 10-pound beast slide uncooperatively when you try to violate them. Bust the plastic off the dead bolt and it reveals a scarier-looking steel shackle. The Dremel took a battery-killing 15 minutes to get through one link, and we still needed a second cut to slide the neighboring link out. Your bike is safe.
2. Blackburn San Quentin
Like any U-lock, this presented a tantalizingly long expanse to work with, but the hexagonal profile of the 18-mm-thick alloy steel makes it hard to find a good angle. The saw got through in about eight minutes, but we'd have needed a second cut to remove the thing: It locks on both sides. And by that point we didn't have the juice to go full-power for another eight minutes.
3. Trek U-Lock LS
Our bolt cutters and hammer got nowhere against Trek's 13-mm hardened-steel shackle. But the big 11.5-inch-long U, which makes for hassle-free hitching, offers plenty of room for sawing. In four and a half minutes, we were clean through with the Dremel and sliding off the opposing piece; unlike the Blackburn, this locks on only one side.
WIRED Light and intuitive. Spare design makes it the best-looking of the group.
TIRED Antitheft protection runs to only $1,500.
$60, trekbikes.com
Rating: 5 out of 10____4. Kryptonite HardWire 1518
Cables are deterrents, not defenders. Even Kryptonite gives the HardWire a 5 on its 12-point security scale. The lock can withstand a hammer attack, but so what: A pair of 24-inch bolt cutters (far from the biggest available) got through the 15-mm braided-steel key cable in two minutes. The Dremel took 30 seconds.
WIRED Light, flexible, and portable. Six-foot length reaches both wheels.
TIRED For friendly areas only. It's about as daunting as a licorice whip.