Jay and I have been having an email conversation about this topic. I'm not going to quote him directly because I think that's unfair and maybe easy to take out of context. But the basis of his intent is to make sure that the builders of bigger/heavier crapwagons use big enough spreader plates to keep their cages from punching through rusty tinwormed sheetmetal. The use of 24 square inch spreader plates isn't mandatory so much as it is a suggestion, as indicated by the use of the words "are generally required" in the rule. So long as the cage is properly functional, the use of smaller spreader plates will not cause a team to flunk tech. But if I were building a new cage on a new project (which I'm about to start), I'd use larger plates.
As regards other orgs, BMWCCA and NASA both require 9 square inch minimums, PCA and SCCA don't state minimums. FIA regs for WRC cars require 18.6 square inch minimums (120 cm squared). So Jay's picked a bigger spec (6x4/5x5/8x3, basically) just to be on the safe side. Also, according to an above post, the 24 square inches need not be all in one plane, so I think if you're building a boxed or plinth mount for your cage (as is necessary on some cars where you can't land right on the will panel), the box/plinth counts toward that 24 square inch number anyway. YMMV. Good luck.
Pat Mulry, TARP Racing #67
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