DIY - Prototyping undertrays
 

Instructables Link

Just thought I should blow my own trumpet. It should prove useful.

Next month (if it all works out and the result is positive) I'll do ABS ones, so that they look good...

Very nice!

I think your "reasons" for the OEMs not doing it aren't quite right though- I would put the reason at not being able to service the car easily. That IS how the dealerships make their money- working on the cars after the sale.

No, my undertray doesn't extend past the bottom of the radiator, it covers no maintainance items except possibly the air-con gas reservior. The rear one covers only the fuel tank (as stated in the instructable).

Incedentally it appears to work. The pair have apparently dropped 0.3l/100km (according to factory display), and the car has noticably less wind noise....

Ah, ok. I was thinking that your tray covered the entire length of the car.

Even with a full tray they can always add access panels. That is what I intend do do.

You have to understand that while you drive your car on the road at a nice pace with abundant air and usually at short distances, when manufacturers make a car, they engineer them to survive extreme conditions, including 100+ degree weather with full load capacity with the AC on and in stop and go traffic. In order for a car to function with an undertray and survive this and more it would take much more engineering, exotic materials, and money. This is why cars do not come with undertrays, save for the ones that cost north of $100k. I saw a whole story with car engineers about the matter several yeas ago. Heat and longevity are the problems.

I did the testing. Saved 0.4l/100km...

I also tested the cooling system performance with and without the trays, no difference. The only downside is that anything that goes through the grill opening either goes through the radiator or gets stuck. There is no more option for birds to fall out under the car, they just stay there and rot if I don't know they are there

Oh I should have mentioned my driving during testing covered a very wide range. Hot, cold, wet, dry, city and country (and any combination of those). And a couple of mountain ranges too.

And just for good measure, some 150kph cruising in 35*c weather...

the 2011 Audi A8 has a factory underpanel
http://i678.photobucket.com/albums/v...underbelly.jpg

And my 02 Infiniti Q45 has factory under panel for the first 38 inches.....just at the transmission.
also angled deflectors infront of the front tires.

there is a service panel that opens to reach the oil filter and the nut.

http://i678.photobucket.com/albums/v...pgq45014-3.jpg

Had I not installed a full body kit which lowered the profile 2 inchs and created a gap to the panel, I would not have made a new one.

Most new cars are quite smooth on the underside and have at least partial undertrays...you can even fit one to most older cars as well. I was referring to complete belly pans like those found on the Mercedes SLR.

http://img12.imageshack.us/img12/1143/sspx0214.jpg
http://img12.imageshack.us/img12/2594/sspx0213.jpg
http://img518.imageshack.us/img518/6392/sspx0219.jpg
http://img259.imageshack.us/img259/8250/sspx0218.jpg