I have 2 older slightly over weight Shih Tzus that I wanted to be able to take along on my Trikke when I take my larger dog out to run her.  I had to be careful that they were large enough for the dogs to be comfortable in but not too bulky for me to fit on the Trikke as well.  Mission accomplished.  Though they are not touching, I am able to stack one above the other and attach them to the main post.  They are spacious enough for the dogs to sit comfortably in them and compact enough that they do not interfere with my steering or control.  The added features I didn't pay attention to when I ordered these 2 pet carriers would actually make it easy to transport my dogs just about anywhere in the world I would want to go.  Durable,great quality and definitely a great price.