Not a lawyer, but talked about this with one once and this is what I remember. By definition you can't steal something that belongs to you. The fact that someone else stole it doesn't make it stop being yours. However it might still be illegal to take it back if doing so involves breaking other laws, like breaking and entering, assault, or what have you. It might not be crazy to risk a trespass, since those generally aren't enforced even when they should be. On the other hand in the USA entering someone's home uninvited can give them legal grounds to use deadly force on a presumption of self-defense, even if your bike is in their back yard. So not only would that be illegal, it could be very dangerous. I'd bet dollars to donuts that anyone inclined to give advice on the subject would say eat the loss and move on.

Strangely there are jurisdictions where if your stuff is in a pawn shop and the pawnbroker claims he didn't know it was stolen, he might have the legal right to recoup what he paid for it from you!