I almost feel bad for posting this here <| sep |> I don ' t care what his original comment says . The photo clearly shows nearly half of the tower has been cut away , it ' s an absolute hack job at that ! If you cut a section out of the strut tower it WILL fail at some point . <| sep |> It does use external energy when the user pulls the bike back out they are helping preload a spring . When the bike is inserted , the spring pulls it up . With a welladjusted spring and a lowfriction slide , it can seem nearly effortless . But the system surely has to be adjusted to match a particular bike for that to be the case . It wouldn ' t lift a tooheavy bike all the way to the top , and a toolight bike would take significantly more effort to pull back down .