All bike locks can be broken, but a sturdy lock and savvy locking strategy will greatly reduce the risk of your bike being singled out by thieves. This article compares the leading styles of bike locks.

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Bike U-lock

This widely used style offers your best deterrent. The bulky locking mechanism resists hammers, chisels and the like. Its horseshoe shape can limit leveraging—provided it's not way oversized for the bike. The goal is to reduce the amount of space in which a thief can insert a crowbar and leverage enough oomph to pop it apart. U-locks come in various sizes. Typical usage:

  • Small to medium models lock one wheel and your frame to a fixed object.
  • Large models lock both wheels and your frame to a fixed object.

The higher-security locks offered by many manufacturers, such as Kryptonite and OnGuard, come with limited bike warranty programs. Check the particular model of lock for complete details.

Cable Locks

Bike cable lock

These are versatile and adaptable but generally offer less theft deterrence than U-locks. On their own, they may be suitable for low-crime areas. Elsewhere, they are a good choice to use in combination with a U-lock to secure easily removed parts (e.g., seat). Many have integral locks; others require a separate padlock. Some feature sliding sizing or an armored coating. A few newer models feature stylish designs and even come in colors!

Chain Locks

Bike chain lock

Tough enough for high-crime areas, these locks use a specially designed chain link that disallows leveraging and resists hacksaws or chisels. Be sure to invest in a padlock that's just as sturdy—thieves can easily cut through thin locks, no matter how sturdy the chain. The downside? Chains are heavy and bulky, so they are best for stationary uses.

Wheel/Seat Skewers

Locking bike wheel skewer

Quick-release wheels and seatposts are, unfortunately, as convenient for thieves as they are for bike owners. Great for high-crime areas, locking skewers disable the quick-release feature and make it a lot tougher to steal. They’re easy to install but require a special wrench that comes with the skewer.

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Other Lock Styles

These styles are occasionally used but are not usually carried by REI.

O-locks: These are designed to stay mounted on the bike. Modeled after the concept of wheel "boots" placed on illegally parked cars, O-locks simply stop the wheel from rotating. They are generally too small to be attached to fixed points such as a signpost, so are less secure than other choices.

Cuff locks: Just as the name implies, cuff locks can attach your bike to a secure post. The middle hinge is specially built to resist tampering.

Bike Lock Keys

Keyed locks use either flat keys or cylindrical keys. Cylindrical keys got a bad reputation in years past when it was discovered some locks of this style could be picked by a ballpoint pen. Newer models have solved that problem so now either style is equally effective.