Underbody tray using spandex fabric
 

So I was just reading about this bicycle while researching diy faired bikes: https://www.lightningbikes.com/f40.htm
And clearly the very first thing to jump to is, why not do this to our cars? A quick search shows spandex material to be $10/yard, which is far more expensive than coroplast, BUT after some searching I found this site: https://www.texactive.com/product.sc?...6&productId=72 That's $4/yard x 55" wide (which I think should be enough maybe depending on stretch and how much body/rocker panels curver underneathe for 4 way stretch with one way water permiability! Plus $8 flat S&H is really cheap for bulk fabric.

The first thought for this was for my truck because it has a very big steel skeleton of a frame that'd be easy to hook this too and far easier to just get 6 yards of this than to get 3 panels of coroplast to line up right (stupid 22' truck). But now I'm thinking why not do all the cars if it works well and I might as well order extra because next time I order would be $8 S&H again but if I just spend that now on 2 yards of fabric that's almost enough to do the festy :-) That car is so small...

Anyway as for mounting I was thinknig self tapping screws at angles and sewing loops so I could easily stretch and hook under tension and remove for annual inspection/oil change/whatever.

But my MAIN concern is what to do with the exhaust. You guys using coroplast what do you do? The exhaust is sometimes a good 2" up from whatever frame/skin I"ll be using on most cars, is this enough your plastic sheets don't melt? Do you coat in some header wrap or something or that insualation stuff that looks liek aluminum foil? Plus on the Festy the exhuast hangs down below the bottom of the body where I'd want this, probably sticking about 1/2-1" up into the flat area that stretching this out would create. Is there something I can wrap the exhaust in that won't melt and allow this to attach with tension right on the exhaust or do you guys think it will still be too hot.

What are your thoughts, good idea worth trying or not enough gain to make it worth it? I was thinking it'd really help to create a lower boat tail too, easily can wrap tight around an aluminum bar skeleton or even make a cheap/ permanent/sportsbra looking grill block.

From reading a lot here most doing bellypans out of plastic use sheet metal around the exhaust, or don't cover the exhaust, they just get as close as they comfortably can.

Being a drycleaner and having lots of experience with this type of fabric (most women's blouses contain some level of Spandex now) it is very sensitive to heat. Heat will cause Spandex to shrink, and loose its elasticity. Even if you work around the exhaust I doubt this will last long, be prepared to make new "underwear" for your vehicles at least on a yearly basis, if not sooner. Coroplast or aluminum sheet metal if installed properly will last the life of the vehicle.

-Jay

EDIT: I was just thinking... Not a really good idea. If it tears and gets snagged on your driveshaft it could cause some problems. I'd stick with coroplast or sheet metal.

yea that stuff melts/ gets weak like jay said

dont forget while stopped it looks safe but id hate to have it blow up onto the driveshaft/snag a stick you ran over and wrap it around a wheel...if i were to do it id want somehitng a tad more rigid... or make a ridgid backing via chicken wire (light and only has 1" hexagonal holes, cheap too) easy to bend and attach that way

For that matter, fabricate a piece out of chicken wire, then once you have it test fit cover the chicken wire in fiberglass resin. Chicken wire will tear Spandex, but make an excellent frame for Fiberglass.

-Jay