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Old 06-02-2021, 11:04 AM   #7 (permalink)
Aero Wannabe
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Join Date: Dec 2007
Location: NW Colo
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TDi - '04 VW Golf
90 day: 55.54 mpg (US)
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coroplast for belly pans

I have had a coroplast belly pan on my VW Golf for 10 years. I have some things for you to consider, some Dos and Don'ts.

1. I believe coroplast is suitable for a belly pan if it is well supported. It is used seal up the bottom of modern camper trailers here in the U.S. It is cheap and doesn't rust. However, it can sag and is not particularly heat resistant near exhaust systems.

2. As Julian has stated, I recommend building a supporting framework to attach the coroplast to. Build it stronger think you think you need to. Sudden wind gusts at highway speeds can generate a lot of force on your attachment points. Julian has measured downforce on his car from his belly pan. The curved pan is sucking the car down to the road. You don't want this thing coming loose on the highway. If you do not weld you can use aluminum angle and rivets or locking nuts and bolts. Riv-nuts are great for attaching the framework to the vehicle and coroplast to the frame using fender washers and Lock-Tite. You can purchase an inexpensive Riv-nut tool from Harbor F. Design the framework so it can be removed for servicing. A belly pan can accumulate water, snow, mud or dust over time. You may want to have some places for it to drain itself.

3. Manufacturers usually leave the cat and the muffler uncovered. A full belly pan can trap heat between the pan and the floor of the car. The muffler can be fairly flat. Make your supporting frame flush with the bottom of the muffler and surround it and leave it open to the bottom.

4. There may be places where metal is better than coroplast. On my car I have a rigid aluminum "Panzer Plate" under the engine and radiator as a skid plate. Looking at your photos, covering the front part in this way may be time and money well spent. This will be more durable in the event of an impact with road debris.

Click on my avatar and you can scroll through some photos of mine. I feel that a belly pan can be some of the lowest hanging fruit for aero gains. Also, I just switched to LRR tires and the early results look very promising. If you could afford a second set of lightweight rims with narrower LRR tires, that may help too.
60 mpg hwy highest, 50+mpg lifetime
TDi=fast frugal fun

Originally Posted by freebeard View Post
The power needed to push an object through a fluid increases as the cube of the velocity. Mechanical friction increases as the square, so increasing speed requires progressively more power.
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