Bicycle locks

This post explains how to choose a good lock for locking a bicycle. How to properly lock a bicycle is explained in this post: Locking a bicycle.

Choosing a good lock

Chain is as strong as it’s weakest link. That is why it is important that both the chain and the lock itself be hard to break or pick.

Padlocks – size and design

Padlocks should be such that they are hard to pick, or break. If it is a padlock for a chain, it should fit snugly around the chain. For a thinner chain it is better to have a smaller lock that fits tight, than a large one that leaves a lot of room to insert a bar and use leverage to break it open.

Lock cylinders

Lock cylinder should be such that it is hard to pick. That means a good key and well protected mechanism. Combination cylinders are generally less secure, better are those with a key. A type of key tells a lot about the cylinder quality.

The last key, Abloy rotating dic cylinder, is one of the hardest to pick. If the lock mechanism is put deep inside the casing (like in the picture above), it makes drilling also a problem (anti drill plates are usually installed), which leaves the thieves to look for an alternative method: cutting, breaking, but the cylinder itself is usually a safe link in this situation.

Bicycle locks – types

There are several basic bicycle lock types:

  1. Chain (and a padlock)
  2. U-lock
  3. Cable (with or without it’s own padlock)
  4. Folding lock

All the lock types are good. If one carries two locks, it is a good idea to combine a cable with one of the other 3 types. This because it takes different kind of tools for those locks: cables are usually cut, while the others are sawn, or broken (or cut if they are too thin, later on that).

Whichever type one chooses, it is important to make sure the lock cylinder and padlock (if the lock type has one) design are good – like explained in previous headings.

Also, one should never choose a lock that is not heavy. Steel is heavy. If a lock is light, it doesn’t have (thick) enough steel. It is as simple as that. A good lock can easily weigh over 2 kilograms.

Steel hardness is another important factor. It is measured in Rockwell (HRC). Optimal hardness is 65 to 70 HRC. Good producers give that information, while the less good don’t even know it.

Here is explanation of lock types with strong and weak points:

1. Chain

Chain with a padlock

Chain with a padlock

Chain should be of hardened steel, such that the core is hardened as well. It should be at least 10 (preferably 12 mm thick). Hexagonal profile (so that bolt cutters press on a wider area, creating less force per mm).

Locking mechanism and lock should be as explained in previous headings.

Advantages: Second most flexible lock type (behind cable). It allows easy locking around trees, through both frame and a wheel. You take a long chain and put it like you want to.

Disadvantages: weight. A long chain is often quite heavy. 12mm links and 1.5 meters long chain can weigh up to 3 kilograms. Also, it is impractical to carry. Modern bikes have cables and housings all around and long chain needs to be wrapped around some part (top tube, or seat tube usually).

2. U-lock



The same as chains, except here thickness shouldn’t be below 12 mm. Lock should be chosen like it was explained in the heading about locks.

Advantages: lowest weight per level of protection. Moderately easy to carry (it usually comes with an adapter holder for the frame). Even without one it can easily be put on a bike’s rear rack (if it has one).

Disadvantages: THE lowest flexibility. To use a U-lock, one needs to find a post that is not too thick. Even then it can hold frame, along with one wheel if it is close enough.

3. Cable

Cable for locking bicycle

Cable for locking bicycle

I’d recommend it as an additional, next to one of the other lock types. The thicker the better. 10 mm is decent. With a good padlock or attached to another lock for keeping closed.

Advantages: the most flexible, easy to carry.

Flaws: a bit easier to cut than other lock types. Good as a backup lock.

4. Folding lock

Folding lock

Folding lock

Made of several steel rods, connected together. Here dimensions and thickness are not that crucial. If it is made by a renowned manufacturer with a good cylinder, then it is as safe as a 12 mm thick chain or U-lock. The weakest point of these locks are the joints.

Advantages: among the easiest to carry (comes with a frame mounted holder). More flexible than a U-lock.

Disadvantages: limited flexibility. In spite being better than a U-lock in that department, one often finds themselves wishing for just 10 more centimetres of length, or just a bit of flexibility to the sides.

Two is better than one?

The claim is often true, with one big “but”. Two good quality locks are better than one good quality lock. If, however, instead of one decent lock (that is hard to cut, or pry), two cheap, easily cut locks are chosen, that will hardly improve theft protection. It is always a good thing to have at least one really good lock, with an additional lock (for locking wheels for example). Cable is a good choice for a second (back up) lock. Use the better lock to lock the bike’s frame to an immobile object, and the weaker lock to back that up, or to lock the wheels so they too can’t be removed and stolen.


Even a well locked bicycle with a good lock takes just about 20 minutes to hack. If the thief uses a battery powered angle grinder, it is just a few minutes “work”. So no method is 100% safe. However, if a bike is better locked than the other bikes in the street and it doesn’t look more expensive, there is a much greater chance it will wait for you where you had left it.

In contrast, cheap bad locks, poorly locked bicycles are taken within a minute or less, with ordinary tools every small thief has, or even without any tools.

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One Reply to “Bicycle locks”

  1. I’m waiting for a u-lock that consists of a hard steel core covered by a reasonably thick aluminum layer and a heavy Kevlar sock.
    I don’t expect it would be heavier than the current all-steel models and would resist grinding (aluminum clogs the grinding wheel) and be impossible to hacksaw without removing the Kevlar and getting through some hard steel.

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