The Best Bike Locks

The 18mm shackle is the whole argument. Shackle diameter is the single number that predicts how long a lock survives a grinder, and 18mm is the top of the consumer range. Kryptonite rates it 10/10, its highest score, and it carries Sold Secure Gold certification — meaning an independent body physically attacked it under timed conditions. That's a real signal. Certification costs manufacturers money, and cheap locks skip it.

The cylinder holds up to the boring attacks too. Grinders get the headlines, but plenty of bikes disappear because someone picked or drilled a lazy cylinder in seconds. This uses a disc-style keyway that resists both, and a sliding dust cover keeps grit and rain out of the mechanism. Owners who leave bikes outside year-round report the key still turns smoothly after long stretches of weather, which is more than you can say for budget locks.

The small opening is a security feature, not just a size. The interior measures about 3.25 by 6 inches. Less empty space inside the shackle means less room for a thief to slide in a pry bar and lever the thing open. Fill that gap with your frame and the rack and there's essentially nothing to work with. Add the patented anti-rotation shackle features and twist attacks stop being productive.

It doubles as the lock for everything else you own outside. Kryptonite pitches it for gates, tool boxes, ladders, grills and lawnmowers, and that's not marketing fluff — an 18mm shackle is overkill in the best way for a shed or a trailer hitch. If you've got an e-bike in the garage and a mower you'd rather keep, one lock covers both. Registering the lock also makes you eligible for Kryptonite's key replacement and anti-theft programs.

Flaws but not dealbreakers

The mini frame won't reach around everything. Thick bollards, wide rack rails and fat fence posts are simply out of range. You'll sometimes end up locking in a compromised position — through the rear wheel only, say — which throws away the security you paid for. Scout your usual parking spots before you buy. If the racks near you are chunky, get the Standard instead.

It's genuinely heavy, and you'll feel it every day. At roughly four and a half pounds, this is the kind of weight that sags a messenger bag and makes itself known on a long ride. Some owners give up on the frame bracket and just throw it in a pannier. If your commute is hilly or your bike is light, that's a real daily tax.

The bigger frame solves the problem people actually hit. A mini U-lock is only as good as the anchor it can reach around. The Standard's longer shackle clears the wide rack arms, thicker poles and railings that stop a mini cold, so you can get the frame and rear wheel through in one pass. That's the correct locking technique, and being able to do it consistently matters more than a couple of millimeters of steel.

16mm hardened steel is still in premium territory. Below about 12mm, a lock is a suggestion. From 16mm up, portable grinder discs start burning out and the job gets loud and slow. This shackle sits at that threshold and uses the same max-performance hardening as our top pick, plus the patented anti-rotation features that make twist-and-cut attacks unproductive.

The everyday details are thought through. The keys have ergonomic heads designed to keep you from bending or snapping one in a cold, stiff cylinder, which is a failure mode owners of cheaper locks run into more than you'd think. A sliding dust cover shields the keyway. And the included FlexFrame-U bracket lets you mount the lock in several spots on the frame instead of the one place a rigid bracket allows.

It's the lock to buy if you only want to buy one. You get New York-series engineering in a shape that works at the office rack, the grocery store, the café railing and the train station. If you commute daily and you'd rather not think about whether your lock fits, this removes the question.

Flaws but not dealbreakers

The bigger opening cuts both ways. More room inside the shackle means more room for a pry bar if you don't fill the space. Get in the habit of pulling your bike tight to the rack so there's little slack, or you hand a thief the leverage the mini design denies.

It's the priciest pure U-lock here and it's just as heavy. You're paying a premium over mid-range options for the brand's top-tier engineering, and you're still carrying about four and a half pounds. If you park in a low-theft suburb, this is more lock than your risk profile calls for.

Double bolting removes the easy leverage attack. Most U-locks latch on one side of the crossbar, which gives a thief a pivot point to work against. The Granit X-Plus 540 locks into the body on both sides at once, so there's no single weak hinge to twist against. ABUS gives it 15 out of 15, its top score, and the square parabolic shackle shape adds resistance against bolt cutters, jacks and saws.

The material consistency runs all the way through. Cheap locks save money by hardening the shackle and leaving the body soft, which is where they get defeated. Here the shackle, the case and the supporting elements of the mechanism are all specially tempered hardened steel. The ABUS Plus disc cylinder resists picking and drilling. Nothing here is the shortcut a thief looks for.

The included USH bracket is the sleeper feature. Lock brackets are usually terrible — they rattle over every seam in the road, they slip, and eventually you stop using them. The USH holder clamps the lock tight to the frame and stays put. If you're going to carry four pounds of steel on your bike rather than in your bag, this is what makes that bearable.

The long shackle gives you reach the minis don't have. At 11.8 inches of shackle height, you can get around posts and rack designs that force a mini U-lock into a bad position. It's a genuinely versatile shape for street parking.

Flaws but not dealbreakers

Four pounds in a long shape is awkward to stash. The 12-inch shackle doesn't drop neatly into a backpack the way a mini does. Plan on using the bracket, because bag carry is clumsy with this one.

Sold Secure certification isn't part of the pitch here. ABUS uses its own 15-point scale, which is credible but internal. If your bike insurance or your building's bike room requires a specific independent rating, check the policy wording before you commit.

The 90cm reach changes where you can park. U-locks fail you at the thick bollard, the wide railing, the odd-shaped bike corral. This one wraps around all of it, and it can catch the frame and both wheels in configurations a U-lock can't manage. If you visit varied destinations — an office garage, a café rail, a friend's porch — that flexibility is worth real money.

It doesn't give up security to get that flexibility. ABUS rates it security level 15, the same top mark as its flagship U-lock. The bars and housing are specially hardened steel, and the rivets joining each bar are designed as a shield against saw blades rather than as the weak link folding locks are usually accused of being. The XPlus cylinder is the same high-resistance mechanism ABUS puts in its best locks.

It's kind to your paint and quiet on the bike. Every bar wears a soft, grippy sleeve, so you can cinch it against a carbon frame or a nice wheelset without leaving marks. The included SH bracket holds the folded block flat against the frame, and it ships with a rain cover for the cylinder and two keys.

For an e-bike, the shape solves a specific problem. Thieves who can't take the whole e-bike often go for the battery and its mounting points. A folding lock can be routed through areas a rigid U-lock simply can't reach, so you can secure more of the bike with one device.

Flaws but not dealbreakers

It's the heaviest and most expensive lock we recommend. At 1,670 grams it outweighs several U-locks here, and it costs more than any of them. You're paying a real premium for versatility, so if you always lock to the same standard rack, that premium buys you nothing.

More joints means more things to maintain. Folding locks have rivet points where a solid shackle has none. They're engineered for it, but grit and neglect are harder on hinges than on a single bar. Keep them clean and lubricated, and don't leave it folded wet all winter.

You get flagship shackle thickness for a fraction of the outlay. At 16.8mm, this sits above the New York Standard's shackle and just under our top pick's. Thickness isn't everything, but it's the number that determines how many cutoff discs a thief burns through. Getting into that range without paying flagship money is the reason this lock is here.

The X4P mechanism locks the shackle at four points. Most U-locks secure at one or two. Four contact points spread the load, so pulling, twisting and levering attacks have nowhere concentrated to work. Combined with the tight 90 by 140mm interior, which leaves almost no room for a pry bar, it's a hard lock to attack with hand tools.

The kit is more complete than you'd expect. Five laser-cut keys, a universal mounting bracket, a co-molded crossbar and a rubberized shackle that won't chew up your paint. Most locks at this level ship two keys and a bracket that rattles.

It's the right lock for a mid-value bike in a mid-risk area. If you're locking a commuter at a campus rack or a suburban station for a few hours, this is the level of protection that matches the risk without you resenting the purchase.

Flaws but not dealbreakers

No independent certification is listed. OnGuard doesn't advertise a Sold Secure or ART rating here, so you're trusting the specs rather than a third party's timed attack test. That also matters if your insurer asks for a certified lock after a theft — the paperwork is easier with a Kryptonite or ABUS.

The interior is small and unforgiving. At 3.54 by 5.51 inches, it's tight even by mini standards. Measure your frame tube and your usual rack before you buy, because a lock that won't reach around your anchor point is worth nothing.

Stock comes and goes. This one is frequently hard to find. If you want it, buy it when you see it rather than planning around it.