Got me some free Coroplast, learn me IT class legal F/R under-trays.

So, the next build-in-progress project will be front and rear under-trays. The SCCA IT rules for them are not totally clear to me. The part that IS clear is that the front tray cannot extend rearward beyond the front edge of the front wheelwell opening and cannot be profiled/raised in the center (more Venturi effect not allowed), and the rear tray cannot extend forward beyond the rear edge of the rear wheelwell opening.

What else can I do, and NOT do, when designing and mounting the trays. I'm not after down-force, but rather drag reduction, especially at the rear where the underbody flow slows and lifts up to merge with the top flow after the trunk lid. I have an idea for the rear, but it involves trimming a notch in the bottom edge of the bumper cover about 3 inches x 60 inches. Basically I want to make the rear tray into a pseudo-splitter, much like this https://www.google.com/imgres?imgurl=http%3A%2F%2Fwww.aprperformance.com%2Fimages%2Fproducts%2FAB-820519.jpg&imgrefurl=http%3A%2F%2Fhonda-tech.com%2Fforums%2Fhonda-acura-28%2Feg-rear-bumper-under-diffuser-2118269%2F&docid=a6LDDin_LQOtUM&tbnid=EM0pWCKH3xrFCM%3A&vet=1&w=450&h=300&bih=638&biw=1366&ved=0ahUKEwiH9qXB0pzQAhWHhlQKHYZ-B_0QMwhIKA4wDg&iact=mrc&uact=8

Is this allowed, provided it stays withing the stock body lines?

Just out of curiosity, does that coroplast say "Trump" on it anywhere? I'm considering getting a bunch of free coroplast as well, but none of it is big enough to make anything good out of without bonding sheets.

Got me Trump, a Killary, and a Gary Johnson Plain old super glue should work fine on polypropylene.

Come on guys, I KNOW some of you have the rules knowledges I am looking for...

The Hillary signs around here are a lot cheaper. They're just a thick, printed plastic bag over a frame, no coroplast.

No help on the class rules, but since your goal is drag reduction, I'd try and close up the leading edge of the rear undertray to avoid a "parachute" effect. So long as the rules allow it.

Come on guys, I know several you of you can answer my undertray rules question!

I can't speak explicitly to the rules, but every IT car I've seen has had undertrays/diffusers in single plane- no curves, no reliefs.

The front is pretty cut and dry- It should be flat, cannot extend beyond the front of the wheel arches, and cannot protrude out from the front edge of the bumper lip (else it'd be a splitter, and that falls into a different set of rules).

The rear is definitely stickier, but I think* I am interpreting the rules correctly in that it can't extend beyond the rear wheelwell, it cannot be curved or profiled but CAN be mounted angular, as long as it follows stock body lines (i.e. doesn't have to be parallel to the ground, but has to be flat). I'm also pretty sure the diffuser 'tabs' (not sure what the technical terms for them are) cannot extend outward from the triangular plane of the flat portion, with relation to parallel. So that in theory means that if your flat plane rises 4" from front to back and is 18" long (these are made up #'s), your fins cannot be any longer than 18" or lower than 4" at the high end, following ground-level to 0 at the low mounting point.

I'm sorry that this is very non-technical in explanation. Too much coffee, and in my brain it is clear, but might not translate to text very well. Basically, and I COULD BE WRONG, but I interpret IT class rules as you cannot extend beyond OE fasia, they have to be flat/planar, panels should be uninterrupted (no reliefs), and you cannot drop anything below your established mounting heights.

The front needs to be as described above.

As I read the IT rules, we are not allowed a rear diffuser other than what came on the car originally. Cannot even add holes in the rear bumper cover to let the trapped air out...

I'll add that if you make it/them out of Coroplast, make a bunch of spares and make them very easy to swap out because you'll need to. Under trays are next to splitter lips in the hierarchy of "aero component morbidity while racing".

Also, nothing actually sticks to polypropylene. Very tenacious flexible adhesives (Goop!, Shoe Goo, Sikabond) will work. Perhaps laminating 2 plies w/ Weldwood solvent-base contact cement and incorporating steel fender washers at attachment points isn't a bad idea.

Thanks guys, I think I got it: No curves or 3D profiling, no altering/material removal from the bumper cover, does not have to be parallel to the ground but no part of it may hang lower than the lowest mounting point.