Safe Running

Question
My Goldens LOVE to run along side me as I bike around the neighborhood. I've topped out at 3.5 miles for them, at a pace I could never maintain if I was running myself - like 8 to 9 miles an hour. They love it, and seem recovered in just a couple hours. My question is: Is this too much? Is it just right? Is it safe to go farther if they are up for it? I don't want to hurt my dogs (2.5 years old, running for only 6 months) and not know it. Thanks

Answer
That would be too much for a younger dog.  I am not sure you should push them much more.  Too much impact of running on pavement will eventually get to their joints.  Keep them lean too.  

Your dog definitely should be narrower at the waist than the hips and chest.
You should be able to easily feel the ribs, but not see them.  Each dog is
different.  Standard recommendations are a good place to start, but each dog
must have its food adjusted to its individual needs. Here is a link to a good illustrated guide,
http://www.longliveyourdog.com/twoplus/RateYourDog.aspx