While no bike lock is impenetrable, a top-rated U-lock can provide substantial protection. U-locks, which are also called D-locks, are tops on experts' lists of the best bike locks, and many thieves will leave a bike secured with a U-lock in favor of easier targets.
If you live in a higher-crime area and need serious security for your bike, reviewers say it's hard to do better than the Kryptonite New York Fahgettaboudit Mini (Est. $85). OutdoorGearLab.com's Rylee Sweeney calls it "hands down the toughest bike lock we tested." Experts like the Fahgettaboudit's 18mm hardened steel shackle, which is slightly thicker than several comparable models and helps the lock resist attacks from bolt cutters and hacksaws. The center keyway adds a level of protection as well; experts say these are tougher to attack than side-mounted keyways.
While reviewers say the lock provides top-notch protection, they disagree on ease of use. Weighing 4.5 pounds, the Fahgettaboudit Mini is heavy for a U-lock. At 3.25 by 6 inches, it's also smaller than others, and a few owners say that makes it difficult to secure anything but their bike frame. Others praise the small design, saying it's easier to transport and makes it difficult for a would-be thief to get a tool between the lock and post. If the lock is too small for your wheels, consider the longer Kryptonite New York Standard U-lock (Est. $100), which some users prefer for its 4-by-8-inch size. The lock doesn't come with a mounting bracket, something that owners say makes transporting it more difficult.
The Fahgettaboudit Mini comes with three keys, one of which has a light. Owners appreciate additional features such as a protective vinyl coating and sliding dust cover. You can register for up to $5,000 of anti-theft protection from Kryptonite online within 15 days of purchase. This coverage is beefier than most, but many say it's more trouble than it's worth since pieces of the broken lock must be sent to Kryptonite as "proof of lock failure" -- and many thieves don't leave evidence behind.
If you're looking for a more economical U-lock, the OnGuard Brute STD (Est. $50) performs nearly as well as the Fahgettaboudit Mini in some expert tests. The lock resists all attempts at sabotage except an angle grinder in tests by PopularMechanics.com, and Slate.com's Scott Elder can't saw through the shackle or dislodge the lock with a hammer. The hardened steel shackle measures nearly 17mm.
Several reviewers describe the Brute STD as a "beast," and at 4.3 pounds, it is just slightly lighter than the Fahgettaboudit Mini. The Brute STD has a longer shackle, roughly 4.5 by 8 inches, so it's a better choice than the Fahgettaboudit Mini for beefier bike frames or for securing both the frame and rear wheel. However, users say the larger size makes it a challenge to carry, and the included mounting bracket doesn't seem sturdy enough to support its heft. In fact, owners of the Brute STD complain that it's heavy and easily falls from its mount, requiring transport in a backpack or basket instead. If you need an even longer shackle, the Brute LS U-lock (Est. $50) has you covered at roughly 4.5 by 10.25 inches.
The Brute comes with five laser-cut keys, including one with a micro light. A vinyl coating helps protect your bike frame from nicks and scratches. The lock comes with a $5,000 one-year theft protection plan that isn't available to customers in the state of New York. Like Kryptonite, OnGuard requires you to send in the broken lock to receive coverage.
If you need something cheaper and more compact, the Abus U-Mini 40 (Est. $45) is a small but tough U-lock that won't break the bank. It has a 14mm double-bolted hardened steel shackle, which is a bit thinner than those offered by the Fahgettaboudit Mini and Brute STD.
At 3.15 by 5.7 inches, the U-Mini is slightly smaller than the already-small Fahgettaboudit Mini. For that reason, some reviewers recommend it as a secondary lock, but many others have no problem using it as their primary lock. The 2.2-pound U-Mini is also roughly half the weight of the Fahgettaboudit Mini and Brute STD, making it a strong contender for anyone who doesn't want to be weighed down by their bike lock. Reviewers note that no mounting bracket is provided, and they say that's a feature that they miss.
The ergonomic U-Mini has "soft touch" housing to prevent paint damage to bikes, and reviewers say that also keeps the lock from getting damaged during drops. It comes with four keys and is available in red or yellow. Abus does not appear to offer an anti-theft protection plan like Kryptonite and OnGuard.
Experts often recommend using a U-lock with another lock in order to keep both your frame and wheels safe. One well-reviewed combination is the Kryptonite Series 2 Standard (Est. $40) package, which comes with a 13mm hardened steel shackle U-lock and a 4-foot double-loop KryptoLok cable. Together, both should be able to protect your bike's frame, both wheels, and possibly even the seat, says Eric Hansen of TheSweethome.com. A handful of reviewers say this lock has been defeated by bolt cutters -- if you're in a high-theft area, you may want to upgrade to the heavier-duty Kryptonite Evolution Mini-7 U-lock with 4-Foot Flex (Est. $55), or pair a cable of your choice with the Fahgettaboudit Mini.
At 4 by 9 inches, the Series 2 U-lock is generous enough to protect beefier bike frames, but still squeaks in at just under 3 pounds -- lighter than both the Fahgettaboudit Mini and the Brute STD. If that's too big, you can pick up the Kryptonite Series 2 Mini package (Est. $40) which pairs the same cable with a 3.25-by-7-inch U-lock. The package also comes with a U-lock mount.
The Series 2 U-lock has a protective vinyl coating and comes with two keys. Some reviewers do say that the lock isn't smooth to operate and requires too much fiddling. The U-lock also has anti-rattle bumpers to reduce noise while riding. You can register for up to $1,500 of anti-theft protection from Kryptonite online within 15 days of purchase, but Kryptonite will require you to send in the broken U-lock, which isn't always possible. The coverage does not extend to the cable.