Do you find that your dog's behaviour changes when a motorbike passes him while out on a walk? This is probably because he is scared of them...
(Q) My dog lunges at motorbikes. When they are parked or waiting at the lights he isn't bothered, but when they're moving he tries to lunge right into the road. I've had him on a very short lead near roads since discovering this behaviour to avoid any accidents.
(A) Trainer Elizabeth Kershaw says: The most usual reason for the lunging behaviour that you describe is a fear response to motorbikes - which isn't surprising given the noise and smell of these vehicles. Lunging is a popular choice for the fearful dog because after the lunge, from the dog's point of view, the bike usually goes away. This puts lunging in the category of a successful ploy - "I got rid of the monster".
It will take a long and careful period of desensitisation to change this behaviour and involves finding an area where you know motorbikes are going to be present, finding the distance away from them that he finds tolerable plus a bit more, and gradually getting closer through a programme of training and play until he is comfortable in their presence. Your best bet is to find a good behaviourist who can build such a programme for you and help you through the stages.