D-Lock's (also known as U-Lock's) are the classic when it comes to securing bikes, and for good reason. They are ideal for bike security as they offer strong protection against a range of attacks and are effective because your frame is protected on all four sides. Solid materials and no moving parts outside the lock mechanism are an excellent starting point for the strongest resistance possible. While some of these locks will be heavy, they are much more portable than a chain lock and far tougher than a cable lock. D Locks are very stiff meaning they’re easy to fit around your bike and a stationary object. They are also recommended by the Gardai and insurance companies.