I used to bike with my 9lb rat terrier mix - she loved it. I just didn't go as fast because she had 3x the ground to cover as my GSD did - And conditioned her to longer runs/ watched her for signs of fatigue. Just common sense stuff.
Danielle, owner of...
Fraggle Rock Collars
Fraggle Vom Richcreek CGC CA
Red Dog's Reconnaissance Man CGC
General Patton Vom Winter Storm