page_title: Bicycle lock
section_title: U-locks and D-locks
hierarchical_section_title: Bicycle lock / U-locks and D-locks
caption_attribution_description: English: Stolen bicycle with only front wheel left. The scene is in front of a public library in Helsinki, Finland. Note that the wheel itself could easily be stolen by cutting the spokes, if the rim and hub were of any value to the thief.
context_page_description: 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.
  Quick-release levers, as used on some bicycle wheels and seatpost fasteners, are a security vulnerability, because they allow the wheels and saddle to be easily removed. Unless such easily removable components are secured while the bicycle is unattended, they are vulnerable to theft. Sensible locking strategies address this by locking these components in addition to the frame, or by taking the vulnerable components, such as quick-release front wheels, away from the bicycle.
  Locking devices vary in size and security, the most secure tending to be the largest, heaviest and least portable. Thus, like other security equipment, bicycle locks must balance the competing interests of 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 uncommon in some countries. A bike locker is not a bicycle lock.
context_section_description: 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, parking meter or other pole installed securely in the solid ground. 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.
  For a time, many U-locks used a tubular pin tumbler lock. However, most tubular locks can be picked by thieves using a common disposable Bic pen. U-locks with tubular pin tumblers should be avoided, though most manufacturers no longer offer them.
  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.
caption: Front wheel is locked with U-lock, but the rest of the bicycle is gone.
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