Dogs will chase anything that moves. I have two dogs and they love
chasing me when I ride off. They will also chase any car that passes
, running along the footpath/sidewalk at up to 60kph. They don't
seem to go after trucks though, the size difference must be a factor.

It also works in my favour though, I can exercise them quite easily
by riding 1/2 mile up the road and back a few times. 
