Let's remember, kids, that the wear on the road that a vehicle does, is not a linear function of the vehicular wieght, or even pounds per square inch on the road. Trucks and cars stress a roadway in ways that a bike could never. The great weight of a vehicle pressing down on the road, with variable pressure, from bumps, and the vibration created from this process, going at great speed will make small cracks grow. Just as a finger tapping on a brick, will never do anything, a sledgehammer, tapping on it, will quickly turn it to dust. I don't think that bikes do any damage to roads, what so ever. We don't exactly clean the air and water from our activity, but we are some of the few people who don't foul it. Damn we're good( or should I say, not bad)!