Once you’ve trained your dog how to run alongside you while riding your bicycle with the bicycle dog runner, your dog can graduate to the bicycle dog n roll automatic leash. Like the dog runner, this advanced device allows hands-free operation, keeping your hands on the handlebars where they belong. Dog n roll extends easily and rolls up automatically, so it remains at the optimum length and never tangles. The unit is easily mounted under the bicycle’s seat and will enhance the outdoor experience for both you and your dog. High quality German engineering and design. Suitable for round seat posts with a diameter of 1.1 – 1.25″.