If his wall is hollow with wood lath behind the plaster, you really need to screw into a stud. The wood lath will only be about 1/4 in thick, not enough for the hook to anchor into even if you are lucky enough to get the hole into the lath and not into the gap between them. Another problem is that the wood lath will flex a little from the bike's weight and the jarring of hanging the bike. The flexing will eventually lead to the lath separating from the plaster. The result is that the plaster cracks and pulls away from the wall. If you have plasterboard behind the plaster the plaster won't pull loose from it, but the plasterboard won't hold the hook. The better way to solve the problem is to use a 2x to bridge across two studs. If all else fails for locating the studs, drill a small hole behind where the 2x will be located and insert a small diameter stiff wire (coathanger) to feel for the stud location. Measure distance left and right of the hole and you'll locate the inner sides of the studs. Be sure to allow for centering the hole into the stud. Also, for safety's sake, borrow a studfinder that also detects live electrical wires. You really don't want to drill into a live wire inside the wall. Even if you don't get shocked or start a fire, it becomes a major headache to repair.

Walt