I watched a video from youtube where lockpicking lawyer recommended a Kryptonite chain lock due to being harder to break into with an angle grinder because it's not stable versus an U-lock.

Does this make chain lock superior to U lock since an angle grinder is the only way to break either locks but with the chain lock it's harder?

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4 Answers 4


U-locks are vulnerable to angle grinders, which are noisy and slower, but also to nail guns, which are extremely fast.

Here is a video showing someone destroying a U-lock with a nail-gun that uses .22 cal blank cartridges to knock a piston into the lock mechanism:

You need to be careful with a U-lock to have a really good one and arrange it in a special way that makes breaking with a nail gun harder.

Chain locks can be cut by sufficiently strong cutters, but you may hope that the thief who just strolls around has only some weaker ones and will choose a different bike that only has a wire lock. Also, the cutters are bigger and harder to hide when working with them.


Depends totally on what tools your local bike thief is carrying at that moment.

If the miscreant has a jack/ram then the U lock can be forced apart quietly in a minute.

If the blaggard has an angle grinder, both a chain and U lock can be cut, but it's noisy and obvious. The chain will need to be held in one hand while cutting with the other, and the black nylon outer sock may create a snagging hazard.

A common tool for the discerning light-finger is the large folding bolt-cutters, where a 36" or 48" unit can fold up to about half that and be concealed under a jacket. These are also mostly silent and can cut most chain on the lower end of the spectrum They can even cut cheaper U locks.

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From https://www.rakdistribution.net/36-inch-folding-bolt-cutters

One U lock can't secure the front wheel to the frame at the same time as the rear wheel, so you need something else. A chain helps extend the range of your locks. Two U locks might work well also, but they may not reach around fixed locking points like a rack or a wall shackle. A fence post or tree would be right-out.

Every bike can be stolen eventually, regardless of how many locks you put on. Your best options are to make it less-attractive, or take the bike inside with you.

  • 7
    If its Mr LPL he'd pick all the locks silently anyway, rotate the bike, and lock it up again to mess with your head :)
    – Criggie
    Commented Apr 26, 2023 at 4:20
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    Doesnt look like that bolt cutter has a chance to cut the chain lock i pictured so chain lock wins?
    – Lightsout
    Commented Apr 26, 2023 at 4:30
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    @Lightsout if you return to your bike and it's still there, then you won. Today. I never lock my bike at work, because its inside with me. If I had to leave it outside, I'd use 2 U locks and a chain otherwise its a long walk home.
    – Criggie
    Commented Apr 26, 2023 at 4:41
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    I generally wouldn't bother using 2 D-locks to lock to the same item. If a thief can jack open one lock quietly, they can jack open two. If they can cut one lock noisily with an angle grinder, they can cut a bike rack with many locks on it more quickly than they can cut two locks (quite likely more quickly than they can cut one lock). If they can cut one lock quietly with bolt croppers they can cut two locks - but not very one fat lock. 2 solid locks are still useful if your bike racks have separate loops for the front and rear wheels, or similar
    – Chris H
    Commented Mar 15 at 13:55
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    Jacking attacks can be mitigated against by using smaller locks so the jack can't fit. Partial mitigation is also achieved but a locking technique that fills the lock with bike (e.g. both chainstays or both seatstays plus the back wheel). Apart from making it directly hard to get a jack in, it means they'd have to damage the bike in the process of breaking the lock, reducing its resale value by a lot.
    – Chris H
    Commented Mar 15 at 13:58

U-locks tend to have much thicker shackles while being lighter and more compact.

In my opinion the only advantage of chains is that they tend to be longer and flexible which makes it possible to wrap them around bigger objects or more components of your bike. For example you can put most chains through the front wheel, through the frame triangle and around a tree.

If you tension a chain you can cut it with an angle grinder all the same while a short U-lock can be hard to get to without risking damage to the bike. So it very much depends on the circumstances and how exactly the lock is used.

Personally I quite trust and like my Abus Futura 64. It has an 11mm shackle while “only” weighing 726g. The compact size is both an advantage and a disadvantage. Chains with that kind of thickness tend to weigh several kilograms.

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    The OP appears interested in the security aspect, not weight or convenience. Chains, all other parameters being equal, provide better security than U-locks.
    – Pete
    Commented Apr 27, 2023 at 10:47
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    @Pete: But how many chains out there have >14mm thick links? So you can’t really buy “all other parameters being equal” (unless you buy a super tanker anchor chain, which is probably not hardened). A chain with >14mm thick links would probably weigh 5kg or more at a reasonable length which really becomes impractical. Even when the chain is not transported, wrapping a 5kg chain around your bike becomes hard and you have to be careful not to damage the frame paint and components.
    – Michael
    Commented Apr 27, 2023 at 13:38
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    @Pete and Michael motorbike security chains can certainly have up to 16mm hardened links. If you don't have to carry it, there are situations where that could be useful for a proper bike. And motorbike chains are normally covered in a nylon sleeve to protect your bike's paint
    – Chris H
    Commented Mar 15 at 14:03
  • wrapping a 5kg chain around your bike becomes hard and you have to be careful not to damage the frame paint and components I don't see any problem in wrapping 5kg chain around my bike if I do it right: not touching bike chain, derailleur and other sensitive parts, touching only frame. And yes, 16+ mm bike locks exist on the markets, there are many of them
    – Suncatcher
    Commented Apr 13 at 1:25

A chain-lock will provide better security than an equivalent U-Lock.

A good quality chain-lock (e.g. Sold Secure Gold Level or higher) would only be vulnerable to an axel-grinder (which unfortunately thanks to battery-powered grinders is a possibility with professional thieves), which isn't quiet and should take at least a minute.

It's possible to lever open a U-lock, which is usually quicker and quieter.

Drawbacks of chain-locks are weight and transportation.

As an aside, insurance policies often define a minimum rating of lock used.

Rule of thumb is the lock should cost 10% of the bike price.

The best protection, from a cynical perspective, is parking next to a nicer looking/more expensive bike which has a cheap lock...

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    Commenting this because an answer would be overkill: Remember, locks only stop honest people! If I want your bike, you your car, or laptop, into your home bad enough it WILL happen. Period. However, how long it takes, and how much noise I make while doing it is something your choice of security measure can effect to the point where YOUR bike is no longer an attractive target. As for the lock price, for a RoT I'd agree, but in this day and age KNOW YOUR MATERIALS because there is a lot of priced up fancy labeled garbage out there. IMHO, make friends with a machinist if you want good locks ;)
    – Tank R.
    Commented Apr 27, 2023 at 13:20
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    I'm not sure about the 10% rule of thumb. Considering the price of bicycles over the last 3-5 years, i don't imagine there are many $800 locks out there
    – Andy P
    Commented Apr 27, 2023 at 13:31
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    @AndyP it's just a rule of thumb though and works well for regular bikes
    – Hobbamok
    Commented Apr 27, 2023 at 15:04
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    @AndyP There are not many $8,000 bikes out there, either. (Sure, there are, just not many. Like, very few.) Commented Apr 27, 2023 at 15:25
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    I personally prefer to invest more than 10% into my lock. My goal when using a lock is to keep my bike, whatever how much it is worth, but I get that it is only a rule of thumb.
    – olliebulle
    Commented Apr 28, 2023 at 0:59

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