Bicycle lock
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A bicycle lock is a physical security device used on a bicycle to prevent theft. It is generally used to fasten the bicycle to a bicycle stand or other immovable object.
An important difficulty in preventing the theft of a bicycle is that the wheels are easily detachable from the frame, and that unless both wheels and frame are secured, the parts not locked can easily be carried away after being detached. The most secure locking method therefore is to lock the wheels and frame to each other and to an immovable object.
Locking devices vary in size and security; the most secure tending to be the largest, heaviest and least portable. Lesser equipment is used to deter attempts by less skilled and determined thieves. Thus like other security equipment, bicycle locks must compromise between security, portability and cost. Some are made of particularly expensive materials chosen for their acceptable strength and low density.
An alternate defense is the provision of lockable boxes in which the whole bicycle is locked. This also safeguards other equipment such as lamps, tools, spare tubes etc, against all but the most industrious thief, or one equipped with heavy equipment or power tools.
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[edit] U-locks and D-locks
A U-lock is a rigid metal ring in the shape of the letter U. The U part of the lock attaches to a crossbar section, and for this reason they are also called D-locks. To lock the bicycle, one locks it physically to some other object, such as a big tree, a rack securely in the ground, or a flagpole. Locking the bike frame to the wheel is not recommended because, although it can't be rolled away, the entire bicycle can still be lifted and carried away.
U-locks are more secure than most other kinds of locking mechanism because they are more resistant to cutting with high-leverage hand tools such as bolt cutters. However, they are still vulnerable to some types of exploit. For instance, if there is enough space for a thief to fit a jack into the U, the jack can produce enough leverage to break the lock. Like all locks, U-Locks are vulnerable to power tools. Certain U-Locks with a late 20th century Tubular pin tumbler lock can be easily picked by thieves, so cyclists should avoid these models.
[edit] Chain
A chain lock is a lockable chain. It often has a key or a combination lock attached to it. A long enough chain can pass through both wheels, the frame and attach the bicycle to an immovable object.
Chains vary widely in their security level. If the chain is made from basic iron or steel, perhaps bought from a hardware store, it can easily be cut with a relatively inexpensive pair of bolt cutters. Chains specifically designed for locking bicycles are also available. These chains are made of a much harder steel alloys and the links are often shaped in a manner that deters bolt cutters, such as with a hexagonal cross-section. A chain is also a convenient way to secure the cycle's wheels.
A chain is only as strong as its weakest link, which may be the lock. Although a cheap keyed or combination lock would be an appropriate match for a hardware store chain, a specialized chain necessitates a specialized lock such as a mini u-lock. Many chains are far too big and heavy to be practically carried around by a cyclist, so it is common for cyclists to leave such chains permanently at a convenient location, such as near their place of work.
[edit] Cable locks
Cable locks are in many ways similar to chain locks. Cable locks often come with the locking mechanism already permanently integrated. Otherwise, a length of cable with loops on both ends can also be used.
The main advantage of cable locks over chains is the ease of transporting them. Many cable locks are made of spring cable that automatically coils itself when released. Even a straight cable can be coiled by the user into a more manageable shape than a chain.
Simple cable locks, however, are only sufficient for use in low-risk areas. Even the largest diameter unprotected cable can be quickly cut with bolt cutters. Better cable locks such as the one shown on the right have overlapping steel jackets threaded over the cable. This can make it much harder to cut the central cable.
Many cyclists use a long cable to secure bicycle components (such as the wheels or seat) in conjunction with a bicycle lock or padlock, which can be used to secure the frame. Special strong cables are available which are made with a loop at each end continuous with the cable, which enable linking with a locking device.
[edit] Wheel lock
Also called an O-lock or ring-lock, this is a mechanism mounted on the frame that immobilizes the rear wheel by moving a steel bolt through the spokes to prevent motion. It uses a straight or circular bolt which extends from the housing. This type of lock, found particularly on bicycles in Scandinavia, the Netherlands, China, and Japan, prevents riding the bicycle but does not secure the bicycle to a stationary object. Some models have an optional cable or chain that plugs in to the body of the lock to enable the bicycle to be secured as well.
This type of lock is very effective and convenient for securing a bicycle against opportunistic theft, when the bike is left unattended momentarily. They are also very convenient for securing the wheels, especially when they have a quick release system instead of axle nuts. As a consequence, only locking the frame is needed, to secure both the frame and the wheels.
[edit] Locking skewers
Locking skewers replace the existing quick release skewers on a bicycle's wheels and seatpost clamp, quick release skewers enable removal without tools. This reduces the need to lock these parts of the bike since now their removal requires tools. One type of locking skewer uses the same design as a normal quick release skewer, except after clamping the skewer the (keyed) handle may be removed.
Another type of locking skewer uses a uniquely-shaped nut that can only be turned using the matching socket/key, which is typically a wrench-like tool that is small enough to fit on a keychain. Though expensive, locking skewers provide additional security and convenience. Locking wheels with an additional U-Lock or removing the front wheel and locking it to the frame and rear wheel would provide the highest security. A disadvantage is that if the owner loses the special tool then they will not be able to undo the skewer, and will need to obtain a spare tool from the manufacturer. The same type of uniquely-shaped nut used for the locking skewer can also be found for suspension forks, V-brakes, and solid-axle wheels in addition to regular wheels and seatposts. Manufacturers such as Pitlock and Pinhead offer services to supply additional lock nuts to an existing key number registered by the owner. Even though a determined thief could eventually defeat the skewer's lock nut by using a power tool, e.g. by grinding a screwdriver slot into it or simply cutting it off, locking skewers provide convenient protection against theft of bicycle parts in areas where locked bicycles are not left unattended for long periods of time.
Less expensive options include replacing standard quick release skewers with skewers that need a standard hex key to be opened. Despite hex keys not being very rare, this method still guards the bicycle from casual opportunists, needing the less common tool and more time to be removed. Five-sided hex key skewers exist which bring some of the benefit of a locking skewer at a lower cost (hex keys are usually six-sided). Quicker and cheaper yet, and only effective against thieves unequipped with even a screwdriver, quick-release levers can be tied down by a common hose clamp.
