With 100 yards to ramp up, I'd be going by the dog at about 35mph. Start all the way on one side of the road, then take dead aim for the dog, and then move back across the road as you get just short of him.
Not advisable if you are dealing with either a pack of feral/semi-feral dogs or a group of trained cattle dogs. Feral packs have been known to run full grown whitetail bucks into the ground and a group of Catahoulas (one of the larger cattle dog breeds) can bring a charging bull to a standstill and never back down. At 35 mph, if that lead dog has the drop on you and hits you broadside or gets in front of you, you are going down and the fact that you ran is going to have the whole pack on top of you in seconds.
In my case, I'm a 230 pound rider who was in mile 30+ of a ride on a lightly loaded steel touring bike. I was facing into a 10 mph or so headwind. My chances of outrunning these dogs was next to nil as, even if I got past the lead dog, once the chase is on, it could last for miles.