an amusingly fitting typo.


Yeah, locks of any variety are no match for the right tools.

cables
Thin ones can be cut instantly with appropriate tools. Thicker ones may need a grinding type tool, but I have heard that good bolt cutters can make short work of thick cables. Even if the cutters don't cut cleanly through the cable, they will more than likely sever enough strands that flexing the weak point back and forth for a minute or two will cause the remaining strands to break from fatigue. Fatter cables are somewhat better than skinnier cables, but really no cable is secure with a desirable enough bike when it all boils down.

chains
cheap hardware store chain can be lopped with fairly small bolt cutters in a hurry. Better hardened chain, up to an including the kind of stuff Kryptonite and others use for their top-of-the-line chain locks is no match for an angle grinder and a few minutes of undisturbed time. If you must use chain, get the real deal hardened chain with the fattest links that you can carry.

padlocks
See above, since a padlock is really just a glorified link of chain that opens and closes at the will of it's master. This applies to all varieties of padlocks, from combo locks to keyed locks to whatever. Also, a lot of padlocks will give up the ghost if you whack them hard enough with a big hammer. If you must use a padlock, try to lock your bike in a manner where the padlock is suspended up away from the pavement or other hard surfaces to make a hammer attack much less feasable. Also, avoid flimsy little locks in favor of a beefier padlock.

combo locks
Anything with a combination is instantly vulnerable to means that involve no physical harm. $10 four-dial combo cable locks can usually be opened in under 30 seconds by someone that has half a clue what they are doing. These are not secure at all. Even better combination locks are 100% vulerable if a thief has enough time and patience to methodically work through the possible combinations. If you must use a combo lock of some variety, choose one that is least likely to be vulnerable to brute force (trying all the combinations) and manipulation (feeling beside number wheels with a thin piece of metal for grooves) attacks. Combo locks seem like a pretty bad idea to me in general.

keyed locks
If combo locks are bad, key locks are better, right? Only maybe. Remember the Bic pen vulnerability a zillion Kryptonite U locks turned out to have? Case in point. That aside, many keyed locks are not hard to pick with the right tools, and a pro can open most typical locks in less than a minute if he/she wanted to. Even if you do get a very invulnerable keyed lock, you are still at the mercy of the cable or chain or whatever else is a part of the locking system.

U locks
These have been around since the 70s, and were a bit of a revolution. They have their fair share of quirks too. On some models, the key goes into the end of the straight part, which then has to be longer to accomodate the locking mechainism. Thieves discovered that they could simply snap off this protruding stub with a piece of pipe and defeat the lock. The solution was to put a plumbing tee fitting over the T formed by this intersection of the lock to make it inmpossible to get a purchase on the lock. Modern models are much better designed, with the notable exception of the Bic pen vulnerability to the round key locks. The other major vulnerability of U locks in general is that of force. Thieves can crack most U locks wide open by levering inside the closed lock with a car jack. The best bet around this is to use the smallest U lock that works for you to leave less room inside the U for a jack to be used.



Overall, there is no good solution to locking up your bike. Locks are merely a deterrant, and one that works best when supplimented in various ways, such as by locking up your bike near much more expensive bikes, making your bike visually less appealing, or just riding a crappy bike that few people would want to steal. If you do have an exceptionally theft-worthy bike, lock up with several different kinds of locks. A good U lock, a chain, and a good keyed padlock is a decent combination. A thief would most likely need several different tools to defeat each different lock, making the bike less desirable compared to some road bike locked up next to yours with just a cable.