The Best Bicycle Chain Locks

Chain Thickness

The thickness of your chain determines whether or not specialist tools are required. The thicker the chain, the larger, nosier and less subtle the tools are that are required to use it.

For example a 6mm chain can easily be snipped by bolt-cutters that can be carried in a small rucksack. Anything over 11mm is going to require larger croppers, more leverage and more time. A well-locked bicycle with an 11mm chain will be VERY hard for a thief to bolt-crop. Anything over 13mm will rule out the cropping method and require an angle grinder.

8mm and thinner

This diameter chain, in my opinion, is not worth it. Many of the budget brands that are offered on eBay or at stores like Halfords or Screwfix are 8mm thick. Your local bicycle shop will be full of them.

You could say that since you can’t get past them without serious tools, and that some get a Sold Secure Bronze rating then they are OK to use.

However, an 8mm chain may be cut with even a set of 12′′ bolt cutters (most of these bike-stealing parasites carry larger ones).

Due to consumer pressure, cheaper chains are produced and, obviously, purchased by customers who are on a budget or who believe it to be good enough because a shop they trust is selling it. 

Yes, some 8mm chains are rated Sold Secure Silver but I’d rather use a thicker D-lock than an 8mm chain.

10mm

Due to its more appealing price point, 10mm is a common thickness. 

A 10mm chain is a fantastic choice if you need portability. I’d prefer not to carry one on my person since I wouldn’t want to do battle with it if I ever fell off the bike because I think the chain would win. Some people carry them around their waist but you can carry one in your rucksack, no problem.

It’s important to note that security chains with a 10mm thickness vary in quality. Some will use case-hardened and chemically treated metals where as other will be made of lightweight metal that should never be sold with security in mind.

Some 10mm chains will scrape in with a Sold Secure Gold rating but the same chains also score a 2 our of 5 in the ART tests, so you can definitely do better.

However, there are numerous companies and non-branded eBay clowns who sell 10mm chains that I would barely trust to lift a bucket of water from a well, let alone protect my bike.

One word of caution: if you’re going to use a 10mm chain, make sure it’s from a reputable manufacturer like Abus, Squire or Kryptonite so you can be sure it’s manufactured of high-quality materials by businesses that care about their reputation.

Even gigantic 42′′ bolt croppers will require some work to cut a good-quality 10mm chain, but a toe-rag with a small angle grinder can easily defeat them in under a minute.

11mm-13mm

Chains begin to get serious at this level but they also get heavy and pricier but I think the extra spend is worth it.

For me, the greatest benefit of choosing 11mm or thicker is that you can immediately weed out the majority of the manufacturers of junk chains.

Although Gold-rated Sold Secure bicycle chains start at 10mm, it’s worth noting that the smallest Sold Secure Gold motorbike chain is 12mm thick. I really don’t think thieves that steal bicycles or motorbikes carry different tools, they definitely cross-over.

The more reputable brands, like Almax, Milenco, and Pragmasis, begin at about 11mm and run all the way up to a huge 25mm (more on that, below).

If I was securing my bike at the same spot regularly, the thinnest chain I’d use is an 11mm chain. Yes, they are weighty but not obscene. You can get them in 0.8m lengths, which is long enough for every application.  

The links on chains of this thickness can differ depending on whether they are square or rounded. Round links are far more difficult for angle grinders and bolt croppers to grasp.

You should choose rounded links over square links, in my opinion.

16mm

There are chains between 13 and 16mm but anything above 16mm isn’t bolt-croppable so if you’re going for a chain to eliminate this common tool, 16mm is where it’s at. 

These are not portable, well, not unless you’ve eaten your spinach. You can get 16mm chains in a 0.8m length which is about at light as you’re going to be able to get. I have one this thickness in my company car park. It stays there all the time and the car park gates are closed out of hours, so I think it’s unlikely it would get tampered with.

A 16mm chain is excellent for home security because it can’t be cut with a bolt cutter by hand and takes some time to remove with an angle grinder.

16mm chains are produced by leading companies like Almax, Pragmasis, Squire, and Milenco. Kryptonite’s thickest is 14.5mm which is good but not the thickest out there.

A 16mm chain and a waterproof bicycle cover are effective deterrents for bike thieves if you park your bike outside, say in a communal bike shelter. Most thieves won’t even try and take it on unless it’s worth a serious amount of dosh. They’ll just pinch the bike in the rack with the least security.

If you’re parking your bike at home, you should consider a ground anchor, which means your bike is tethered to a solid object and can’t simply be carried away. They’re not expensive and are simple to install.

19mm – 25mm

A 19mm chain and larger is carrying on with the same ethos as the16mm versions. Basically they’re ‘f*** off’ chains that will require serious tools, time and commitment from the thieving scumbags.

If you really want the best, a 19mm chain is a fantastic option for home security; I have one in my garage. However, it’s not in any way portable. Plus threading the links through your bike is a delicate task – you don’t want to chip your paint work.

You can get 22mm and even 25mm thick chains but for me, 16mm is the best ratio of price to performance. The 22mm chain links weigh almost 1kg each and they’re a health hazard if you leave them in the middle of the garage floor!