Hey Al, its been a while. I have not written about the tubing material. It does make a difference. I had a chassis builder make me a chassis out of an oval shaped tubing once. No wonder the rules specify round tubing only. Not sure if this holds true today but all the "Factory" drivers were not on what the public was riding.
The main thing is that on any chassis the numbers that they "suggest" is what works 80% of the time anywhere. Most people are afraid to step outside the box and try different numbers. The main thing is that you have to look at the drivers build and work from there. For the 425 class and above I would prefer a bigger tube chassis. Another thing people do not pay attention to is the seats on karts. If you look at the front runners, they shave the lip off the seat. This causes the seat to flex and acts as a damper. What they are doing is controlling weight transfer. The rear bumper should be torqued. The sidebars should be loose. Again, it is the little differences that make a big difference.
When I look at the karts that I ran back in the early 2000's the rear was somewhat soft, the waist was wide and flexed a lot and the front loop was not the same. Now, the karts are ultra stiff in the rear, the waist is narrow and stiffer and the front acts more like a torson bar in that it is a constant bend. Back in the day 45 nose, 55 left, and 60-65 cross was the norm. Now you see 48 nose, nearly 60 left and cross anywhere from 58 to 75. If you remember Pat Dotson, he built a chassis with 50% nose, 58 left and 65 cross. That thing was a rocket! It was way out of the norm back then. But look where we are today. What is still neat is that a lot of things that I wrote in my chassis manual still hold true. I have several people on newer chassis running old school numbers and are doing very well. My point is all the numbers must complement each other. Then there are the tires and tire prep.
Msquared - Understanding Chassis Theory and Dynamics