I have an expanding family of grand kids and their cousins. I am thinking about buying($$$$) or building 6 plus fun karts and paving or pouring an oval track.would prefer to build . Any ideas on a proven design ? I was thinking Harbor freight engines and skinny tires to make the little boogers learn throttle control while having fun . also having them weighted similarly when loaded w driver to even things out. Being the fat guy at the rental kart places is just riding around while skinny people go fast.