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Hey all, I found this site after seeing Wayne on CNN, glad to be here!

With my current goals in place I'm stuck hypermiling my 2004 Silverado crew cab V6/M5; so any truck specific ideas are appreciated! My question is, what kind of affect will lowering my stock height truck have on MPG? I haven't heard any buzz on this. A tonneau cover claims 10% increase but I imagine lowering the vehicle would give greater results. What do you think? Thanks!

Tony :flag:

the tonneau cover works great, and worth it to majority of those who drive trucks here. As for lowering, from an engineering perspective, it really depends on the overall height of the truck off the road once it is lowered. If you just want to do it for the gain of fuel economy, it may be better to just get an underbody aero kit (usually has to be self made). I'm not sure of the actual gains, but there are some for lowering the ride.

Mythbusters tested all sorts of truck be modifications and found that the tailgate up is the best position. It makes sense to me that the engineers who designed these trucks made it so the air would pass over the gate.

Mythbusters tested all sorts of truck be modifications and found that the tailgate up is the best position. It makes sense to me that the engineers who designed these trucks made it so the air would pass over the gate.

Thats true if you're only options are tailgate up or down. However, they later tested this further and those nettings are better because of the reduced weight from having no tailgate and it was still able to keep that air cushion in the bed.

Lowering the truck with reduce the frontal area, thus reducing the drag coeffcient and will increase vehicle stability and FE. By how much I'm not sure.

I have doubts that a toneau cover will improve the mpg by 10%. It would require dropping the CD by 20% (from .45 to .36) to get that sort of improvement in JUST HY DRIVING. In city stop and go the cover will actually decrease mpg since the CD isn't as important as the extra 100 lbs. No way will a toneau drop the CD by that much . It is the Toneau selling companies lying -or just being selectively truthful.

Don't buy a Toneau to save fuel unless you drive strictly on the hy ,and I'm not so sure about that either ,since as was pointed out -the engineers know what they are doing. Buy it to protect your stuff.

If you city drive, the net would be a plus -hy maybe not.

Lowering a vehicle and/or installing an air dam are just aerodynamic bandaids to divert air from going underneath a vehicle with an aerodymically dirty underside. Lowering a vehicle does slightly reduce the frontal area by incorporating more of the wheels inside the vehicle's body. An air dam adds frontal area and also creates a low pressure area under the vehicle (this last is useful for racing, but not so much for hypermiling). It can reduce your mileage if overdone. If your vehicle has a smooth underbody (and wheel spoilers, double side skirts, and wheel boattails to clean up the wheel-related aero), then you don't need to lower or use an air dam. And well-designed underbody paneling can also double as skid plates when off-roading.

If you ignore the increase in wheel frontal area, aero drag decreases as you increase the ground clearance, since the air going under the vehicle isn't being compressed and diverted as much. If you ignore where its 3 wheels touch the ground, look at how much ground clearance the rest of the Aptera's body has.

basjoos- I would be better off paneling the underside of the Suburban rather than lowering and skirting it?

I have kinda wondered why the 2000-2003 Suburbans don't get better hy mpg (EPA 17) than my 1998 Suburban.The 2000's got the 5.3 ,and the whole point of that engine was increased efficiency. It also has the better ignition system-coils on plugs. The vehicle "appears" to be cleaner also with more flush bumpers etc. Unfortunately the 2000 on Suburbans went to much wider 265/70 16 vs 235/75 15 taller tires -maybe those bigger tires/wheels stole all the potential increase in FE.

It wasn't until 2004 that Suburbans really got the better FE that GM promised with the 5.3-
14/18 vs 12/17 that the 1996-99 got with the 5.7. If I can scrape up the money,I'll sell my 98 and buy a high mile cheapo 2004 and panel the underside and skirt the rear wheels.
Thanks,
Charlie

see this on big dave he has done it he could provide real answers in stead of mythbusters hype
http://ecomodder.com/forum/showthread.php/finally-got-side-skirts-3761.html

I can tell you what I’ve found.

By putting on a flat tonneau, I picked up 1.5 MPG (on a 18 MPG truck at the time) over a open bed with the tailgate up.

By putting on a fastback bed cover, I picked up another 1.5 MPG (on a 19.5 MPG truck at the time) over the flat tonneau.

By installing a 3” front and 6” rear lowering kit (with slightly smaller front tires) I gained another 1.0 MPG (on a 21 MPG truck) over just the bed cover arrangement.

The jury is still out on the combination of an air dam with side skirts but it looks like the improvement will be in the 0.75 MPG range.

BTW
All my claims are the product of at least 1500 miles of testing over a mixed regime of 35% city driving, 35% rural roads, and 30% Interstate driving. I fill up at the same station and the same pump every time. I think my test regimen is quite valid.

Pickup trucks offer a lot of scope for aerodynamic gains because they are so egregiously boxy to start with. If you cannot get a 33% improvement, you are not trying.

Thanks Big Dave! Very encouraging info! I agree, most trucks have a lot of room for improvement. In my '04 Silverado, the V6s have the same EPA rating as the V8s... very disappointing for my V6. I guess because of aero and weight, have you done anything to reduce unnecessary weight? I have a regular cab so I don't think I have much potential there.

I have not done a thing about weight. Central Indiana is very flat. Best thing I could do about weight is put myself on a diet.

I'd definitely recommend cleaning up your aerodynamics unless you do 75+% city driving. A cheap vinyl tonneau will do wonders.

And well-designed underbody paneling can also double as skid plates when off-roading.



I couldn't see any skids that would help offroading performance helping mileage. The thickness of steel you would use in a skid plate would kinda start adding up if you did the whole bottom of your car.

I have not done a thing about weight. Central Indiana is very flat. Best thing I could do about weight is put myself on a diet.

I'd definitely recommend cleaning up your aerodynamics unless you do 75+% city driving. A cheap vinyl tonneau will do wonders.

weight reduction is very good for city driving also, which I'm sure you know. also if you do pulse and glide ;)