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A bicycle lock is a security device used to deter bicycle theft, generally by fastening the bicycle to a fixed object, e.g., a bike rack. An inherent challenge to bicycle theft prevention is wheels and bicycle seats (seatpost fastener) with a quick-release lever, making them detachable from the frame (on most but the most economical of bicycles). Unless both wheels and frame are secured, wheels can be removed separately. An optimal locking method will secure the frame as well as both wheels — either to a fixed object or to each other. 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 bicycle lockers or a bike cage in which the whole bicycle is locked, but these are rare and uncommon in most countries. A bike locker is not a bicycle lock. Test standards that rate the effective security of bicycle locks are provided by Thatcham and Sold Secure in the United Kingdom, ART in the Netherlands, SSF in Sweden, and VDS in Germany. Tests carried out by the Cyclists' Touring Club showed that all of the locks under test could be broken in less than 42 seconds using either bolt cutters for a cable/chain or a bottle jack for D-locks.〔(【引用サイトリンク】title=Lock it or lose it )〕 ==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 bike rack securely in the ground, parking meter or other pole. Merely locking the bike frame to the wheel is not recommended because, although it cannot 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, most are still vulnerable to at least one type 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. Another common brute force method to break open U-locks is to use a long length (perhaps 2 metre) of pipe to twist the lock open (although this method is more commonly used to defeat chain and cable locks). Like all locks, U-Locks are vulnerable to power tools such as portable angle grinders. A quality U-lock will advertise the material's hardness (relative resistance to grinding), its resistance to prying (expressed in tonnes, or pounds, for example, one might resist to 5 tonnes, which exceeds the 2-tonne capacity of a common car jack), as well as resistance to drilling into the keyhole itself. Cheap imitations of the original cylindrical pin tumbler lock are in use today everywhere, and the U-lock was no exception: all U-Locks with cylindrical keys commercially available can be easily picked by thieves using a common disposable pen, such as the Bic pen. However, locks with the cylindrical key are no longer offered by most manufacturers, and they should be avoided. A very similar type of lock, often referred to as an O-lock, or a "bike club," is a retracting shackle lock. This lock may be more protective as it does not leave space for thieves to insert tools like a car jack which would burst a normal u-lock. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bicycle lock」の詳細全文を読む スポンサード リンク
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