For the Monty Python Fans (Think Sparrows...)
 

So, what is the velocity of an unladen 50-pound pit bull terrier from a rest when tempted by skinny white legs spinning on a bicycle?

(Or, what is the instantaneous heart rate spike experienced by the owner of said white, skinny legs...).

I think the answer to both is "too fast!"

I think its Swallows

OK, Swallows it is.

Sucker was laying in the shade, and I think I surprised him. He sure surprised me. Turned out he just wanted to run - he coulda had me cold. 25.5 miles an hour, for a lot longer than I thought he would run. His jump from laying down to on my wheel was incredible - Cavendish would be envious. So very glad he wasn't hungry...

Reminds me of American Flyers. Here's Eddie: http://www.bing.com/videos/search?q=...2A9E0D&first=0

Dogs speed, an estimate, about 5 mph faster than said cyclist for the first 5 yards, then the cyclist's heart rate comes into play. It goes from the normal average rate for his riding cadence to about 10X that figure, thus sending enough adrenaline to the legs for a burst to say 45 mph for maybe 1/2 mile or, until he explodes, and the dog begins to lick his face as he lays there bleeding and panting.

I can't answer your question, but I do know a big German shepard, with a bigger voice, can cause a dumb kid to put enough force into the pedals to spin the back wheel.

Hmmm,
OP's location: "Location: South of Salem, North of Eugene"

I've got a cousin who lives just outside of Dallas Oregon, and he has one or more Pits that he uses for pulling competitions, wouldn't surprise me if you and his dog(s) were cycling/running partners. I haven't talked to him in maybe 3-5 years though so I don't know if his dogs run loose, he lives on a busy street so I doubt it. But, still, it makes me wonder. And he had Sparrows nesting on his property too.

Was between Jefferson and Millersburg. The Cyclist Eaters live behind Coffin Butte - I don't go there anymore....