look carefully-you can see the hero's little cafe racer peeking out of the top of Energer's head-Photo via Limit's world
"Mazinger Z creator Go Nagai reveals that he had always loved Tetsuwan Atom (astro boy) and Tetsujin-28 (gigantor) as a child, and wanted to make his own robot anime. However, for the longest time he was unable to produce a concept that he felt didn't borrow too heavily from those two shows.and here's the ramp-photo and toy reviewvia Limit's world
One day, Nagai observed a traffic jam and mused to himself that the drivers in back would surely love a way to bypass the ones in front. From that thought came his ultimate inspiration: a giant robot that could be controlled from the inside, like a car. In his original concepts, the titular robot was Energer Z, which was controlled by a motorcycle that was driven up its back via a ramp and into its head. However, with the sudden popularity of Kamen Rider, Nagai replaced the motorcycle with a hovercraft, and the idea was soon forgotten."