TFR: You could enroll in mechanical engineering and study materials.
TFR-Powered: Great InSights! Still, depending on the structure, material and design of the chassis, is there a way to quantity the amount of flex? Also, since a tub design will have alot of reinforcement ribs to increase the sturdiness, and a graphite and FRP chassis are mostly flat, doesn't the extra designs of the tub provide equal if not more? Still, just basing on the material used isn't good enough, but also we have to look at the design.
I think anymore of this... this hobby will become more of an engineering feat.
Ok, if flex is all that evident in plastic tubs, how can we determine if it's really the evil? The infinite question would be "how much flex is good?"