I worry about how dogs think. If my doofus got it into his head to chase a bike, and then got a biscuit out of the deal, a lightbulb would go off in his little mind:

"Hey, if I chase and bark and snap at these bikes, I get COOKIES!! Therefore i shall chase and bark and bite at EVERY SINGLE ONE I SEE! Cool beans!"

My dog is a very linear thinker. He would never make the deduction that: "bikes a nice and friendly, they give me cookies, therefore I shouldn't chase them."