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Fuel Mileage With Cap Or Cover?

Zembonez

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Zembonez Senior Enthusiast

Zembonez

Posted
Posted

I have been wanting to add a shell or nice bed cover to my truck. If you go and read what the bed cover manufacturers say on their websites, they all say their products increase MPG by some magic number (most use 10%) Some of them say that a camper shell actually decreases your mileage by as much as 10%...

 

I don't really want to lose any fuel economy. In the 2900 miles I have had my truck the DIC says I have gotten exactly 16 mpg. Not awful but not a figure I want to see go down! I have an order placed for a Leer 100XQ shell but it hasn't been built yet so it isn't too late to change plans.

 

Anybody got any input?

 

Thanks in advance.

rogerf Enthusiast

rogerf

Posted
Posted

Much of what a cap does to aerodynamics (and fuel economy) depends on the height profile. Keep it to cab-height and it helps alot. Had a taller wedge-shaped cap on a Dakota and could feel the front end get loose at high speeds. That kind drag must cut into fuel economy.

 

On the tonneau covers, could tell from the high-speed distortion of the soft-top on my last Chevy that it's keeping a significant amount of air from catching the tailgate. Currently running a folding hard tonneau on this NBS and seeing a lifetime ave 17.3 on the DIC since new.

Norman Enthusiast

Norman

Posted
Posted

I have a 2007 Sierra, 4.8L Regular Cab, and I'm averaging somewhere in the 15 MPG range with my normal city driving and 17" wheels, no performance mods (no cap or bed cover, either).

 

I'm not all that pleased, considering my truck has had 89 octane gas since day 1.

06Hayabusa Enthusiast

06Hayabusa

Posted
Posted

Not sure of the cap/cover.

 

But did you guys see the mythbusters episode re. the tailgate up or down. They proved twice you get better mileage with it up. Moving air starts to rotate in between the cab and the gate and the air coming over the cab just flows over that bubble. With the gate down it was just all turbulence vs smooth flowing air.

Zembonez Senior Enthusiast

Zembonez

Posted
  • Author
Posted
I'm not all that pleased, considering my truck has had 89 octane gas since day 1.

I would think my RCSB would get better than 16. Pretty bad if you ask me.

 

Guys can i ask what size rims you both have. Im doing a comparision, becuase im getting 19MPG AVE

I have 20 inch wheels and 275-55-20 Pirellis.

 

But did you guys see the mythbusters episode re. the tailgate up or down. They proved twice you get better mileage with it up.

I saw that too. Aerodynamics aren't always as obvious as they look.

FREAKENHYE Enthusiast

FREAKENHYE

Posted
Posted

in theory a large diameter rim/tire combo should be better for freeway riving becuase it will reduce the rpms of the vehicle, but still working on it.

svensk Senior Enthusiast

svensk

Posted
Posted
in theory a large diameter rim/tire combo should be better for freeway riving becuase it will reduce the rpms of the vehicle, but still working on it.

True, but it's more rotational mass to keep moving.

Zembonez Senior Enthusiast

Zembonez

Posted
  • Author
Posted
Zembonez I think you'd be the first nnbs Silverado ever with a big camper shell and 20's. :thumbs:

If I do it, I'll be getting something slick like I had on Fred...

 

Fred0111.jpg

 

This was Barney in 05

 

barney0111.jpg

Schmids5.3l Senior Enthusiast

Schmids5.3l

Posted
Posted

That is pretty slick actually! Maybe Wingnut will give into buying some 20's??

 

What % tint is that??? My G/F wants get my driver/pass. windows tinted for christmas. Rear window is factory tinted.

Zembonez Senior Enthusiast

Zembonez

Posted
  • Author
Posted
That is pretty slick actually! Maybe Wingnut will give into buying some 20's??

 

What % tint is that??? My G/F wants get my driver/pass. windows tinted for christmas. Rear window is factory tinted.

I always use 20% on the fronts. You have to redo it before inspection though. (in Texas 35% is max) I just peel it off and go spend the 50 bucks at my shop. It's worth it. I like em dark so my wife can't see me with my G/F :thumbs:

 

OH and Wingnut will probably charge me for using a pic of his truck.

FREAKENHYE Enthusiast

FREAKENHYE

Posted
Posted
in theory a large diameter rim/tire combo should be better for freeway riving becuase it will reduce the rpms of the vehicle, but still working on it.

True, but it's more rotational mass to keep moving.

 

 

 

Well im trying find out if the extra MPG increase with the 20's will compesate for the weight.

LAGA Enthusiast

LAGA

Posted
Posted

IIRC At the end of the Mythbusters show they reported that tests done by other people, showed that a hard fiberglas tonneau cover reduced drag the most out of other types of caps and covers.

redvett Senior Enthusiast

redvett

Posted
Posted
in theory a large diameter rim/tire combo should be better for freeway riving because it will reduce the rpms of the vehicle, but still working on it.

True, but it's more rotational mass to keep moving.

 

 

The tire & wheel size along with the gear ratio the MFR's install put the engine in the sweet spot of the torque band and larger or smaller tire sizes will move the highway RPM's out of the preferred RPM;s which is on the LS engines at 2000 RPM's.

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