We have two Long haired Chihuahua's
The little girl was fine and _loved_ running along side... until she saw a dog on the other side of the road and decided to go be friends (our dogs love to make friends with other dogs), then I nearly ran her over and got scared for her so we took her home.
The little boy was terrified of the bike and tried to run sideways while watching the bike the whole time. Very funny to watch, but in the end we gave in to him and picked him up to carry him.
He _much_ preferred that idea