Bike locks come in a handful of shapes. The shape tells you a lot about weight, reach and how the lock is put together. Here's the counter-top rundown.
One rule runs through all of them. Wikipedia notes that the biggest, heaviest locks tend to be the most secure, and the least portable1. You trade strength against carrying it.
U-locks (D-locks)
A rigid metal ring with a crossbar. It doesn't bend, so it won't wrap around odd shapes the way a chain does1.
The page on how a lock works covers the shackle and the body. Here the point is the build: one stiff piece of metal, in one fixed shape.
Folding locks
A folding lock is made from connected steel plates that move around on hinges1. Think of a carpenter's folding rule, but in steel.
Wikipedia says this design makes it much more flexible than a U-lock, at similar strength but slightly more weight1.
Chains
A chain is a length of linked metal with a lock on it. Because chains bend, they're easier to secure around tricky-shaped objects than D-locks1.
Chains vary widely. A chain from a hardware store is likely basic iron or steel. Chains made for bike security are often case hardened1.
The weight is the catch. Chains tend to be the heaviest solution, particularly the long or tough ones1.
Cable locks
A cable lock is a steel cable, often with the lock built in. The main advantage over chains is the ease of transporting them1.
The cost is strength. Simple cable locks are only sufficient for use in low-risk areas1. Sturdier ones have overlapping steel jackets threaded over the cable1.
BikeRadar notes that its lighter-weight rating tier typically includes cable locks and folding locks2. Lock security ratings explained shows what that tier means.
Ring locks, also called frame locks
A ring lock is mounted on the frame and immobilizes the rear wheel by moving a steel bolt through the spokes. It prevents riding the bike but does not, by itself, secure it to a stationary object1. It gets its own page: frame locks and wheel locks.
Quick comparison
| Type | Build | Main trade-off |
|---|---|---|
| U-lock | Rigid metal ring with a crossbar | Rigid, so it can't flex around odd shapes1 |
| Folding lock | Hinged steel plates | Flexible, at slightly more weight than a U-lock1 |
| Chain | Linked metal, plus a lock | Flexible, but tends to be the heaviest1 |
| Cable | Steel cable | Easy to carry; simple ones suit low-risk areas only1 |
| Ring lock | Bolt through the rear wheel spokes | Doesn't fasten the bike to anything1 |
Using two types together
Police advice is to mix. The Winnipeg Police Service tells owners to choose a strong lock and combine two different types of locks3. Their cable and chain instructions both say to pair them with another style of lock, such as a U-lock or padlock3.
Details differ from model to model, so check the maker's manual for the one you own.
Notes and sources
- Bicycle lock, Wikipedia
- Sold Secure bike lock ratings explained, BikeRadar
- Bicycle security, Winnipeg Police Service
More lock notes
How an e-bike lock works: shackle, bolt and cylinderWhat's inside a bike lock, and what stops it opening: the shackle, the locking bolt and the key cylinder, in plain words for new owners.
Lock security ratings explainedWhat rating marks from testing bodies like Sold Secure mean, what they leave out, and why e-bikes can have their own category.
What to lock an e-bike to: frame, wheels and anchorsWhich parts of the bike and which fixed objects police and city pages say to lock, and which anchors to avoid.