Originally Posted by
noglider
Given that the ring lock prevents the bike from rolling but doesn't secure it to a fixed object, it seems a lot less secure than a U lock or heavy chain. Given that one needs at least one of those two things in a city, what good is a ring lock?
Usually, one can clip a crap cable lock or snap/BIC a U-lock and ride a bike away. Heavy chains usually deter but even heavy chains can be broken easily with an angle grinder / LN2 and the bike is ridden away easily.
The ring lock on a decent bike where it's welded the frame can't be defeated with any of the usual mechanisms (cable cutter / BIC / LN2 / Angle grinder) without cutting through the frame. Getting around the fender, frame, wheel, etc... makes it a wasted effort to break a ring lock.
Even if the bike is thrown in a truck to be transported away, it's not worth the effort to pick a ring long as no one will buy it used without the proper key.
Having said that, I have seen Baltic thieves take whole bike racks into a truck in CPH and take the ferry back to LT with about 10 bikes, so nothing prevents a thief really. The ring lock just makes it's not really worth it as it has minimal value without the key.