We bought 2 of these, one for each dog. They didn't come with installation instructions, by my mechanically minded husband had them on our bikes in no time. They fit nicely on the back wheel assemblies of our cruiser bikes. We took the dogs for a test spin around the block - I had the hyper-spastic 1 year old 15 lb. terrier mix and my hubby took the calmer, 50+ lb. coonhound mix. I could feel the little guy zig-zagging all over the place at first, tugging against the leash that came with the bar (our little dog can't walk a straight line on a regular leash, so this was no surprise.) The older, calmer dog was a little shy of being so close to the bike, but she got used to it pretty quickly. She's a little overweight, so I was concerned about how she would do going at a faster speed. Turns out, she loves it! And so does the little guy. Once he gave in and stopped zig-zagging, he started running along side me, tongue lolling about, absolutely loving it. As we were riding, we came across a jogger and the little dog lunged at him, pulling the rear of the bike over with him. When we got home, we found that his harness had dug into his chest a bit. I'd read another review where the woman replaced the leash with a bungee cord, so we tried that out as well, to give the dogs a little bit more play in the leash. That worked out so much better with no injuries to the dogs!I hope the manufacturer reads these reviews and changes the leash design to a stretchier material to prevent injuries to the dogs. We also got both of the dogs better harnesses with a mesh chest piece and padded "armpit" straps, purchased, unfortunately, at the local big box store that starts with a "W".We love these bike leashes and would recommend this model above all others to anyone. It keeps the dog to the rear of the bike, prevents him from getting caught up in the wheels or pedals, and gives him the exercise he desperately needs. We took them camping and rode all over the campground with the dogs, much to most of the other campers' amazement. Some thought we were being cruel by making the dogs run, others thought it was a good idea, but their big dogs would drag them down the road. Not so. Once the dog gets into a rhythm with the bike, he runs along happily, and as one other reviewer stated, a tired dog is a happy dog. Our dogs do a noisy dance when we get out the harnesses and go nuts when we get out the bikes. If these things ever break, we're getting another set just like them!