Fool's Errand (Aeromodding GMC 2500HD)

[vskid3]

I finally ordered 10 sheets of coroplast from Home Depot to do some aeromods and seal the bottom of my trailer. (Only $110 and free shipping to store, not bad)

The canvas:


First project was making wheel skirts for my truck, 2003 GMC 2500HD, 2WD, 6.0L gas, automatic. There's roughly a half inch gap between the fender flares and the actual fender. I cut 2 ~3" slots in the flares at the top of the wheel well for the coroplast to slide into and secure it up top. I folded in the sides and attached them inside the wheel well using the existing holes for attaching the flares to the fender. There should be plenty of clearance for the tire to move into the wheel well as the suspension is loaded and they're quick and easy to remove without any tools.

Now for the bad... They both bow out about an inch and they get flapping a bit at speed (50MPH is the fastest I've gone so far). Is this messing up whatever gains the skirts otherwise might provide? I'm thinking of putting a strip of metal on the outside of the skirt and riveting it to the flare to control the flapping while still making removal easy.





I'm also thinking of adding a belly pan, but probably just partial because of the large exhaust. If I do an aerocap it'll have to be removable and collapsible in order to accommodate towing our fifth wheel, any ideas? I won't be blocking any of the cooling area of the grill because it's mainly used for towing, but I'll see if there's any nonessential aero-ugliness that can be fixed.

[elhigh]

EXCELLENT.

I've been wanting someone to do this for some time now. The open space above that wheel is just ridiculous. There have been a couple of other users here that went whole hog but I didn't catch them at the outset, so they were already well on their way when I noticed them. PLEASE make a garage page for your truck so everyone can see how it improves!

You could probably fab up some skirts to close off the huge gaps above the steering wheels. They don't need all that space either.

Absolutely add some metal to the loose edge of your rear skirts. You aren't the first guy to notice that flapping, and the others that did notice it were working on a MUCH smaller scale. I think a strip of aluminum will do.

NOTE: I think you could add more aluminum than you strictly need, and use that to splice in some more coverage. I bet you could bring your coverage further down over the wheel with no ill effects.

On my Honda I have a vinyl skirt over one wheel - mostly I'm just leaving it to see how long it lasts, over six months so far - and its clearance is about 1/4". Obviously your rear suspension is way different from mine but I doubt if it shifts around too much, you can probably get closer than you are and still be clear.

I wouldn't worry about the bowing. It's a long, smooth curve, so flow should stay nicely attached. It's one hell of a lot better than it was before, anyway.

Pan any part of the underside that you can. It's an aerodynamic mess under there, all kinds of crap just poking every whichaway. I think virtually anything you do has the capacity to make it better. Foremost and rearmost improvements will have the greatest effects, but the ones at the middle of the truck will likely be easiest to do.

Paint the coroplast black and no one will ever notice it. Or don't, your call obviously. Maybe you'd like more people to notice it, ask questions, maybe make improvements to their own rides.

I bet it comes out quieter.

SUBSCRIBED WITH A BULLET.

[redneck]

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Looking good...

Instead of using a piece of metal to stiffen up the skirt, try adding another layer or strip of coroplast.

Just buy a spray can of permanent contact glue. Coat both surfaces, wait for it to tack up and press them together. Done.

Pay attention to the direction of the coroplast tubes. If you line up the tubes in each layer it will be easier to bend in one direction

If you alternate the direction of the tubes in the coroplast it will be much stronger but harder to bend. A example of that type of construction would be a sheet of plywood.

By using coroplast instead of metal, you lessen the chance of causing damage to your vehicle or another vehicle should it fly off. (tires, paint, glass)


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[elhigh]

^^

Good point, that.

[vskid3]

Originally Posted by elhigh

PLEASE make a garage page for your truck so everyone can see how it improves!

You could probably fab up some skirts to close off the huge gaps above the steering wheels. They don't need all that space either.

I bet you could bring your coverage further down over the wheel with no ill effects.

I prefer using Fuelly, I'll be sure to make notes on there when each mod is added.

I'm not sure how much I could skirt the front wheels without having to make it hinge. I might get around to it eventually after taking video of the suspension travel to see how low I can go.

(Prius looks very Dr. Seuss in the reflection on the flare)

The skirts are as low as they can go while being inside the fender and not rubbing the tire if the skirts were flat. I don't plan on going any lower unless I add side skirts.

Originally Posted by elhigh

Pan any part of the underside that you can. It's an aerodynamic mess under there, all kinds of crap just poking every whichaway. I think virtually anything you do has the capacity to make it better. Foremost and rearmost improvements will have the greatest effects, but the ones at the middle of the truck will likely be easiest to do.

Paint the coroplast black and no one will ever notice it. Or don't, your call obviously. Maybe you'd like more people to notice it, ask questions, maybe make improvements to their own rides.

I think front and rear pans might be easier on my truck. The exhaust is about even or below the frame rails. I should be able to at least cover from the rails to the running boards in the middle. Running boards probably hurt a little, but I'm short and I love the ones at the front of the bed. Makes it so much easier for me to access the bed. Here's some pictures of the belly of the beast. Links to full size images are below each.

http://i.imgur.com/xhJJtCi.jpg

http://i.imgur.com/D4rdHbM.jpg

http://i.imgur.com/3BIidGr.jpg

http://i.imgur.com/wFmT2Bc.jpg

http://i.imgur.com/0pcvldN.jpg

http://i.imgur.com/M4JxzL9.jpg

I was planning on painting the skirts flat black after I get them all sorted out. I don't want the mods to really stick out and I don't think this coroplast is UV stable.

redneck- I think I'll try gluing more coroplast before moving to the aluminium. Looks like super glue is one of the best ways to glue coroplast.

[darcane]

Originally Posted by vskid3

I think front and rear pans might be easier on my truck. The exhaust is about even or below the frame rails. I should be able to at least cover from the rails to the running boards in the middle. Running boards probably hurt a little, but I'm short and I love the ones at the front of the bed. Makes it so much easier for me to access the bed. Here's some pictures of the belly of the beast. Links to full size images are below each.

http://i.imgur.com/xhJJtCi.jpg

http://i.imgur.com/D4rdHbM.jpg

I was planning on painting the skirts flat black after I get them all sorted out. I don't want the mods to really stick out and I don't think this coroplast is UV stable.

You basically have the heavy duty version of my old truck. I stopped at the engine, but some of my belly pan construction techniques could be useful:
Pics
Description

The running boards are likely not as bad as you think. Some studies have shown that they behave similarly to having side skirts. Plus it gives you something to mount your belly pan on.

My black coroplast on my Civic has been installed three years now. While it's slightly faded, it's still pliable and not getting brittle. I'm not sure if all coroplast is like that.

[aardvarcus]

Your truck is very similar to my extra/hauling truck. (2001 Chevy 2500HD 8.1L Big Block, Allison Transmission, 4x4.)

Stick some thin metal or heavy wire through the cells of the coroplast and that will stiffen it up quite a bit.

I am sure you have noticed the exhaust on these trucks is big, everywhere, and in the way. I would focus on putting belly pans between the frame and the steps first as that would probably be the easiest. I would also look at doing wheel tire air deflectors in front of the treads.

Also you can see the transmission crossmember hangs down below the frame about 2" for no reason. That can't be good for airflow down there. There are aftermarket flush ones available, or it wouldn't be that bad to fabricate.

Nice truck by the way, looks clean and taken care of.

[spacemanspif]

For the front wheels and the front of the rear wheels just make gap fillers out of coroplast to to encourage the air to pass over the wheel/tire and leave the rear open. This way there isn't interference with the turning wheels and your rear skirts don't have to look weird. For the front close up any gaps that exist that are not in front of the radiator like around the headlights and bumper. Belly pan would be nice but a huge ass air dam is easier. I can't see if the truck already has a dam, but it should have had one from the factory, I think. If you don't have one, get one, and then make it longer appoximately as low as your lowest piece (rear axle?) or a little lower.

Electric cooling fan of belt driven? Thought about a chip for the engine for eco and towing modes??

[vskid3]

Originally Posted by aardvarcus

Stick some thin metal or heavy wire through the cells of the coroplast and that will stiffen it up quite a bit.

Nice truck by the way, looks clean and taken care of.

Great minds think alike! I just got back from Lowe's with a couple pieces of 1/8" steel rod. Unfortunately, it still flaps with one rod a few flutes from the bottom. I made a little video of my test drive. You can see the skirt in the mirror. Is this too much flapping?

https://www.youtube.com/watch?v=F4hVTsNRK8E

Paid a little more than I wanted to for the truck, but there weren't many alternatives. It's lived its whole life in the El Paso area, so there's barely even any surface rust. I think the original owner mainly used it as a commuter and the people I bought it from only had it about a year and barely drove it. 118k miles on it now.

darcane- Nice belly pan! I'm going to try to get away with mainly using zip ties, but your way looks like a good option.

spacemanspif- No air dam on it now, not sure if it had one stock. There's really not too much that sticks out below the frame, so I would like to see how much I can cover with a belly pan without ending up with melted coroplast.
Cooling fan is belt driven. Last I looked into it, going electric was pretty spendy and probably wouldn't ever break even. I'll have to explore some junkyards and see if I can find some deals. I've thought about a tuner, but again, probably wouldn't be able to justify it off of gas savings alone. A nice thing about this truck is that the towing mode can be set up as a completely different tune from the regular, so I could have access to an eco and towing/power tune at the touch of a button.

[redneck]

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This is what I use.
You can buy it at Lowes.





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