| A bicycle lock is a physical security device used on | | | | Chains vary widely in their security level. If the chain is |
| bicycles to prevent theft. They are generally used to | | | | made from basic iron or steel, perhaps bought from a |
| fasten the bicycle to a bicycle rack or any immovable | | | | hardware store, it can easily be cut with a relatively |
| object. | | | | inexpensive pair of bolt cutters. Chains specifically |
| An important difficulty in preventing the theft of a | | | | designed for use in locking bicycles are also available. |
| bicycle is that the wheels are easily detachable from | | | | These chains are made of a much harder steel alloys |
| the frame, and that unless the bicycle frame is | | | | and the links are often shaped in a manner that deters |
| attached to an immobile object it can easily be carried | | | | bolt cutters, such as with a hexagonal cross-section. A |
| away after being detached from the wheel. However, | | | | chain is also a convenient way to secure the cycle's |
| if only the frame is locked, a wheel or wheels may be | | | | wheels. |
| stolen. The most secure locking systems therefore | | | | As the saying goes, a chain is only as strong as its |
| lock the wheels and frame to each other and to an | | | | weakest link, which may be the lock. Although a cheap |
| immovable object. | | | | keyed or combination lock would be an appropriate |
| Most portable locking devices need to be quite large | | | | match for a hardware store chain, a specialized chain |
| and substantial to discourage a serious theft attempt. | | | | necessitates a specialized lock such as a mini u-lock. |
| Bicycle locks are generally inconvenient and heavy; | | | | Many chains are far too big and heavy to be |
| although, some are made of materials chosen for their | | | | practically carried around by a cyclist, so it is common |
| strength and low density. An alternate solution is the | | | | for cyclists to leave such chains permanently at a |
| provision of lockable boxes where the whole bicycle is | | | | convenient location, such as near their place of work. |
| locked in. This safeguards other equipment such as | | | | Cable locks |
| lamps, tools, spare tubes etc. | | | | Cable locks are in many ways similar to chain locks. |
| A U-lock is a rigid metal ring in the shape of the letter | | | | Cable locks often come with the locking mechanism |
| U. The U part of the lock attaches to a crossbar | | | | already permanently integrated. Otherwise, a length of |
| section, and for this reason they are also called | | | | cable with loops on both ends can also be used. |
| D-locks. To lock the bicycle, one either locks it | | | | The main advantage of cable locks over chains is the |
| physically to some other object, or locks the frame to | | | | ease of transporting them. Many cable locks are made |
| the rim of the wheel between the spokes, rendering | | | | of spring cable that automatically coils itself when |
| the entire bicycle immobile. | | | | released. Even a straight cable can be coiled by the |
| U-locks are more secure than most other kinds of | | | | user into a more manageable shape than a chain. |
| locking mechanism because they are more resistant to | | | | Simple cable locks, however, are only sufficient for use |
| cutting with high-leverage hand tools such as bolt | | | | in low-risk areas. Even the largest diameter |
| cutters. However, they are still vunerable to some | | | | unprotected cable can be quickly cut with bolt cutters. |
| types of exploit. For instance, if there is enough space | | | | Better cable locks such as the one shown on the right |
| for a thief to fit a jack into the U, the jack can produce | | | | have overlapping steel jackets threaded over the |
| enough leverage to break the lock. U-Locks are also | | | | cable. This can make it much harder to cut the central |
| vulnerable to power tools, and more exotic methods | | | | cable. |
| such as freezing the lock mechanism using liquid | | | | Many cyclists use a long cable to secure bicycle |
| nitrogen to make it brittle and shattering it with a | | | | components (such as the wheels or seat) in |
| hammer. | | | | conjunction with a bicycle lock or pad lock, which can |
| Chain | | | | be used to secure the frame. Special strong cables |
| A chain lock is a lockable chain. It often has a key or a | | | | are available which are made with a loop at each end |
| combination lock attached to it. A long enough chain | | | | continuous with the cable, which enable linking with a |
| can pass through both wheels, the frame and attach | | | | locking device. |
| the bicycle to an immovable object. | | | | |