Racing Frames are typically made of Chrome Molybdenum tubing. This tubing type is very strong and light. Race Car frames are made out of Chrome Moly as well. For example Formula 1 cars have a combination of tubing and composite materials.
Chrome Moly tubing also requires special welding equipment. And if that is not bad enough, you also need to heat up the frame “cherry red” after you have welded it, to get it stress relieved.
Racing Go Kart Frames are designed to be light weight primarily, because weight counts in racing. The more weight, the slower you are.
One thing I have been wanting to dabble with, and that is a fully plastic, or a fully fiberglass go kart. I have never made one, but if you have information, please share it, and we will include that information on this site!