Coroplast undertray thickness

[Otto]

How thick does Coroplast need to be for adequate stiffness and strength in a normal small car?

[Frank Lee]

It all depends on how big the unsupported spans are.

Thick coro = few support ribs
Thin coro= more

and everything inbetween.

Was that helpful? By itself, perhaps not. If you have coro of a certain thickness already I'd say start out with minimal supports and go by feel, judgement, and road test experience to add more supports as needed. For example if I made a bellypan of thin coro with few supports and I could push it up between supports more than, say, 2" with light pressure by hand, I'd consider adding enough crossmembers to bring the rigidity up.

[BabyDiesel]

I am using the thin coroplast for a front and rear belly pan on my Escort. I have it attached with zip ties of all things, no braces! It is not rigid, but it does get the job done.

When I go back and design a more permanent version, I will use the thick 10mm coroplast with aluminum hardware, as Donkey CRX has done.

[freebeard]

Slide welding rod into the flutes. Do the edges like this



A v-notch and wrap the edge with aluminum tape, or a deeper notch and roll the edges before you tape them.

[cowmeat]

I use pallet liners, I get them right down the road from a guy who literally has thousands of them, and I pay 2 bucks apiece. They're thin, super strong, the edges are already sealed, and they're a perfect size to work with on my Insight.

They come in all colors in case you're concerned about belly pan aesthetics.

[Otto]

Well, I ask because 4mm is the standard thickness for Coroplast at local sign shops, but that seems too thin to be stiff enough for an undertray supported by the car's cross members spaced ~2 feet apart.

According to engineering types, in a sandwich structure or I beam if the thickness between flanges is doubled, stiffness is increased 8 fold, so thicker Coro would be much stiffer, and stiffness is what we're after in undertray applications. Local stiffeners of wood dowel rods inserted into the flutes might work well, or carbon fiber arrow shafts if need be.

I also want to avoid aerodynamic flutter.

So, for those who've successfully used Coro for undertrays, what thickness did you use?

[cowmeat]

I highly suggest trying to find the pallet liners because while they're basically the thin 4 mil coroplast, they're industrial strength (so heavy items can be placed on pallets) so they don't require a lot of support. For each pallet liner section I only put a support at each end and one in the middle, overlapped the pallet liners about an inch over the supports, and just screwed them into the supports with self-tapping screws.

To me, they are the perfect size to use, because if something jumps up off the road and tears one up, I can easily replace just that section instead of spending all day under the car replacing the whole belly pan.

They've been on Turtle for almost a year now with no issues. You should be able to find them in your area.