Doubledice, there is a pair of the really big German Shepards near my house. I mean BIG dogs. They can run about 32-33 mph and my bike runs about 36 mph! Just enough to make them give up after about a mile. I have an English Mastiff that weighs right at 200lbs and these dogs make him look like a normal dog. Really BIG and FAST. If I stop, they will play and lick, but if I run they give chase.
It took me about 2 months before I decided to stop and test their personalities. 1 big dog is enough chasing you, but 2 that are family. That will get the blood flowing!