U-lock vs Chain lock: Which is best?

U-locks and chain locks and are undoubtedly the best way to protect your bike. And ideally you would use one of each. But if you’re only going to buy one lock, which is the best, a chain or a u-lock?

U-lock vs chain lock! This is a hotly debated topic and you will hear vociferous opinions from both sides! But the truth is, it’s fairly simple and depends on how you’re going to use the lock…

If you’re looking for a portable lock to secure your bike in the street every day, then you’re probably best off with a u-lock. Whereas if you’re only looking for a lock to protect your bike at home or at work, then the best choice is a thick, high quality chain lock.

Why? Well, if we compare the locks for ease of use, security, and price all will become clear. But before we start, we need to divide chain locks into two distinct groups...

Those that are light enough to carry around on your bike every day. And those that are so heavy that you generally need to leave them in one place (usually at home or at work).

This is because chain locks can be really, really heavy. The absolute maximum thickness for a portable chain is 12 mm. Obviously the length of the chain is important too. (And at 12 mm only the shortest chains are portable!)

But in general, chains that are less than 12 mm thick are light enough to carry around on your bike every day. While chains that are more than 12 mm thick are for stationary security only.

1. Which is easiest to use?

U-locks

U-locks are relatively light and their stiff shape means they are easy to fasten around your bike. However, this rigid shape can also be a disadvantage as it makes transporting them complicated.

You can of course carry them in your bag. But locks get wet and dirty and some u-locks are heavy enough to be uncomfortable in a bag.

So if you want to carry them on your bike, you’re usually dependent on the frame mount that comes with the lock. Unfortunately these are often unreliable, with a tendency to work loose and rattle or even fall off after a while!

The constrained size of u-locks can be another disadvantage. A standard sized u-lock is usually big enough to fit around bike racks and street signs.

But you’ll probably struggle with lamp posts and other wider street furniture. And with the smaller u-locks you may only be able to use bike racks.

Portable Chains

With portable chains, their relative length means there’s always loads of options when you’re looking for somewhere to lock your bike. And if the chain is long enough, you can even secure two bikes with one lock.

Also, because they’re flexible, they’re usually much less complicated to transport than u-locks. Just wrap them round your seat post and you’re good to go!

However, even portable chains are usually much heavier than u-locks. And this can really slow you down when you’re on your bike.

Stationary Chains

For stationary chains, their huge weight is not such a problem. And again, their relative length can be a major advantage at home where you may want to secure two or more bikes at once.

It’s also (very) unusual to have a bike rack at home and chain locks are much better suited than u-locks to the ground anchors you are more likely to use in a bike shed or a garage.

Which is easiest to use Summary

In summary, I think chain locks are just a bit more practical to use than u-locks. With portable chain locks, the ease of transport and the wide range of locking options in the street just about beats the u-lock’s weight advantage.

For information on the best way to carry a bike lock around check out my guide on where to put your bike lock when riding!

And with stationary locks, the u-locks weight advantage is largely irrelevant and since chain locks are better suited to the home environment, they win the day.

2. Which is most secure?

There are some security issues that are specific to each type of lock. But before we talk about those, lets look at one that affects them both…

One of the most common ways that both chain locks and u-locks are defeated is with bolt cutters. Bolt-cutters come in a range of different sizes, from 8″ models that will fit in a pocket, up to 42″ monsters that are almost impossible to conceal.

While very few bike thieves use the biggest 42″ bolt cutters, some of the more organised gangs do. And the 36″ cutters are commonly used by all sorts of bike thieves.

The thicker the lock, the more resistant it is to bolt cutters. And if you want to be absolutely sure your bike lock can’t be defeated by bolt cutters, you normally need a chain or a u-lock shackle that is at least 16 mm thick.

Because at 16 mm, good quality, properly hardened steel is too thick to be cropped by any manual bolt cutters.

For example, the Kryptonite New York Lock Standard u-lock and the Almax Immobiliser Series III chain are both 16 mm thick. So neither can be cropped by bolt cutters.

But just look at the weight difference! While the Kryptonite lock is 4.35 lb (1.97 kg), the Almax is over twice as heavy at 9.15 lb (4.15 kg). And that’s for the shortest version of the chain which is just 28″ (70 cm)!

Whether a chain or a u-lock that’s less than 16 mm thick can actually be cropped by bolt cutters, will depend on the size of the tool, the size and skill of the thief and the position of the lock.

Keeping the lock as far from the ground as possible makes it much more difficult for the thief. But the risk of theft from bolt cutters is very real for both u-locks and chains.

U-locks

U-locks have certain weaknesses that don’t affect chain locks. For instance, they are all susceptible to attacks where something is inserted into the D shaped space inside the lock and then used to force it open.

This could be a crowbar or piece of scaffolding which can then be twisted and with enough leverage will break apart many u-locks. Or it could be a hydraulic bottle car jack, which given enough space, is powerful enough to pop open most u-locks.

While this risk can be alleviated by leaving as little space inside the lock when you use it, it will always remain an issue with the cheaper, standard sized u-locks.

Also, while both chains and u-locks will be defeated by angle grinders, it’s often easier for the blade get an initial purchase on a u-lock, meaning they can be cut quicker.

However, because they are smaller than chain locks, u-locks can have thicker shackles without being prohibitively heavy.

So even the highest security, New York Fahgettaboudit Mini U-lock, with an 18 mm, bolt cutter proof shackle is still portable.

A u-lock with a 13 mm shackle can only be cropped by the very biggest bolt cutters. And even the smallest, lightest Abus Granit Futura 64 150 u-lock with a 11 mm shackle is resistant to most bolt cutters.

Portable Chains

With all chains locks, if there’s enough slack to manoeuvre the lock onto the floor, they are susceptible to attacks where the lock is made brittle with cold compressed air and then smashed against the ground with a hammer.

This risk can be alleviated by keeping the chain off the floor and as tight as possible against the bike.

But the main security issue with portable chains is the link thickness. Since the upper limit for a portable chain is more or less 12 mm, theoretically all portable chains can be cropped with bolt cutters.

And bear in mind that even the shortest, 12 mm chain like the Kryptonite New York Chain 1210 is heavier than the heaviest, most secure, 18 mm u-lock.

In fact, even a 9 mm chain like the Abus CityChain 1010/110 (which is more realistically portable for most people), is at 5.29 lb (2.4 kg), heavier than the vast majority of u-locks!

Stationary Chains

16 mm thick, stationary chains are bolt cutter proof. And in fact, I have never heard of a good quality, 15 mm chain like the Kryptonite New York Legend Chain 1515 being cropped by bolt cutters either.

Stationary chains are also more difficult to attack with power tools. And they’re not susceptible to the leverage attacks that can defeat U-locks. So they are probably the most secure of all bike locks.

Which is most secure Summary

While u-locks have more inherent security issues than chain locks, these can largely be nullified by good locking technique. By this I mean filling up the space in your u-lock with your bike and keeping it as far from the ground as possible.

With chains, although you can reduce the risk by keeping it off the ground, the fact remains that a portable chain will always be more susceptible to bolt cutters than a thicker u-lock. So for this reason, the best u-locks are more secure than the best portable chains.

However, chains that are as thick as u-locks offer the same resistance to bolt croppers and because they don’t suffer from the same inherent security issues and are harder to attack with power tools, offer better protection.

For this reason, the best stationary chains are more secure than the best u-locks.

3. Which is cheapest?

In general, u-locks are cheaper than portable chains which are in turn cheaper than stationary chains.

This is largely due to the fact that when you buy a U-lock you are essentially buying a big padlock.

Whereas when you buy a chain lock you are buying a padlock and a long length of welded steel chain. On top of this, there is just more metal to pay for with chains than with u-locks.

U-lock vs Chain lock Conclusion!

So, if you’re looking for a lock you can carry around every day, usually a good u-lock is better than a portable chain lock.

U-locks offer more security, at a better price, without sacrificing too much practicality. And if you try to bump up the security with a thicker chain, you rapidly loose practicality because they’re so heavy.

That’s not to say that u-locks are the best choice for everyone. If you need more locking options, a portable chain could be better. You might need to lock your bike around bigger objects. Or you might need to lock more than one bike at once.

Or, maybe you just can’t cope with the rubbish frame mounts that come with most u-locks! It’s much easier to throw a chain around your seat post than mess about with an fiddly, unreliable, plastic bracket.

The most secure portable chain is probably the Kryptonite New York Noose 1275. However, with 12 mm links, it’s still really heavy. Perhaps the Abus CityChain 1010 (9 mm) or the Abus Granit CityChain (10 mm) are better options, depending on your security needs.

However, if you can live with the frame mount or find another way to transport your lock, then you get better security and better value with a u-lock.

The Kryptonite New York Fahgettaboudit Mini is the most secure u-lock available today. However, it’s very small and very heavy. The Abus Granit X Plus 540 is bigger, lighter and still offers a very high level of protection.

For stationary security (usually at home or at work), then a thick, heavy chain is better than any u-lock.

They are more secure and much better suited to a home environment where you are unlikely to have a handy bike rack to slip your u-lock round and may want to secure several bikes at once.

The Pragmasis Protector is the best stationary chain. If you can’t find that, the Kryptonite New York Legend Chain 1515 is a good alternative.

So that’s u-locks vs chain locks!

I also have a simple guide to choosing the best lock for your bicycle where I walk you through 3 simple steps to guarantee you find the right lock for both you and your bicycle.

If you’re unsure about which brand of u-lock or chain to get, check out the Abus vs Kryptonite vs OnGuard page where we compare and contrast the three best bike lock brands.

If you’ve decided a u-lock is the best choice for you check out our u-lock buying guide. Or if you think a chain lock is what you need, read more in our chain lock buying guide.

And if you’re still not sure, you can compare the weights, sizes and security ratings of chain locks and u-locks.

But if you already own one or the other let me know why you chose the lock you did. Have I missed anything out? Or maybe you think my conclusions are wrong? Let me know below…