Originally Posted by vtjim
Jeez guys, the Springer works. I've ridden with my dog (~45 pounder) for hundreds of miles (not all at once) with it. The spring eliminates sudden yanking, and the mounting point is low enough that the dog has little (if any) leverage to effect the bicycle's steering. Never had any issues at all. She runs on rider's right, out of the way of oncoming or passing cyclists.
I've used it with my 45 pound mixed breed. She loves it, often she is running on the right in the grass at the edge of the trail. Like any excersise program with any animal start slowly and work up to the long runs. You'll be amazed what your pooch can do. I would say watch out for broken glass and such, but I've found my dog seems to have a very intuitive sense of what's under foot and she's never had a problem.
Ohh please bring water and a bowl.