Tested Valence MPG Before/After

cato · July 2, 2016

That is about the same mileage I think I lost when leveling the truck so while it may not be a huge amount of controlled variable runs, I'd say it is pretty accurate given how much you were able to control the variables. Thanks. At 1 mpg average, for me it amounts to about $175 per year in additional gas expense.

For less than $3.37/ week I'll take better aesthetics ( IMO anyway) over $ savings. Can't even buy a 6pk of beer for that these days. lol

Marticus · July 4, 2016

Wow the valence is one hell of a hot button topic. So here are my thoughts (and no I didn't read all 4 pages). Yes it does affect gas mileage and yes I think the truck looks more like a "truck" without it. So it depends on what you like. I took mine off. I think it looks better and one mile a gallon only bothers me when I'm on a trip. So that's my decision.

I must say though. I like the op's test. Aside from barometric pressure he had a lot of things covered. Haha

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02-tx-z71 · July 31, 2016

Interesting topic.

OldBlue61 · August 1, 2016

I like the looks w/o it better as well. Gas get to $4 (+) a gallon, I may have to put it back on, but until then...

Silvern Sentry · August 1, 2016

To put any myths aside. The air dam (a valance is the term for a "covering" and it does not cover anything) adds exactly 1 MPG under sterile optimized environmental conditions. It has no other function or reason. Fact is most people will never be able to achieve such conditions and certainly not for the entire life of the truck, but it does technically allow GM to show 1MPG better rating on the factory sticker (that is the true reason it is standard equipment).

One thing that is not a myth however is how many dang bolts are holding that on. There is an over abundance of bolts down there, 14 painfully placed upside down bolts one can only get at the buggers with a 1/4 turn at a time. If GM Engineers ever read this, please for the love of god make that thing easier to take off or at least put the bolts on the right way. My battered knuckles will thank you!

OldBlue61 · August 1, 2016

One thing that is not a myth however is how many dang bolts are holding that on. There is an over abundance of bolts down there, 14 painfully placed upside down bolts one can only get at the buggers with a 1/4 turn at a time. If GM Engineers ever read this, please for the love of god make that thing easier to take off or at least put the bolts on the right way. My battered knuckles will thank you!

Ain't that the truth!

02-tx-z71 · August 1, 2016

Yep. Vids I've seen show a lot of bolts.

tnchevy · August 1, 2016

I am now 9 months in running without my air dam. According to my spread sheet I am averaging 18.94 mpg over this 9 month period. The same 9 month over the same months last year with the air dam I averaged 18.95 mpg. In 3 months I will have a good 1 year with and 1 year without to compare with. I don't know if these newer engines get better mpg's with break in time so that may affect this as well but I'll still update my results.

cato · August 2, 2016

One thing that is not a myth however is how many dang bolts are holding that on. There is an over abundance of bolts down there, 14 painfully placed upside down bolts one can only get at the buggers with a 1/4 turn at a time. If GM Engineers ever read this, please for the love of god make that thing easier to take off or at least put the bolts on the right way. My battered knuckles will thank you!

I lucked out. I swapped my chrome bumper with a black one so access was cake.

LTZDaddy · August 3, 2016

Thanks for the 'test' T. good info to know. What I'd like to see though is checking your mileage in the SAME direction. Now *that* would be a true measure of what's going on. Of course headwind, tailwind etc. will always be a variable, and as one post put it, you might do 5 trips and average them together. But basically... running the same road, same direction, within a 60 minute period should be enough to get that data.

On another note.

Studies have shown that tonneau covers reduce aerodynamic drag. SEMA conducted a study in January 07′ that found tonneau covers reduce aerodynamic drag 4.2%-7.8%, depending upon speed.

Who knows that that 4.2%~7.8% figure actually translates to in 'real world' conditions, but it's a real figure. Think an open bed doesn't have drag? Check out a NASCAR truck and see what their wind tunnel test tell them about not having the beds covered. ;)

Of course at city driving speeds I doubt it'd ever be a measurable difference. But at 60 plus, I'm glad I have one.

Also glad I have that fancy air dam/valance as I'd also fall into the group that bought the truck BECAUSE it gets better mileage than some of the competition. Not to mention it just looks so darned good!

@Cato.....

I understand you don't like it on your truck, and that's great, GREAT looking truck, really nice indeed! But being lifted, offset wheels, flares, and big tires, your air dam/valance is the least of your MPG concerns.

Penguin VII · August 3, 2016

Thanks for the 'test' T. good info to know. What I'd like to see though is checking your mileage in the SAME direction. Now *that* would be a true measure of what's going on. Of course headwind, tailwind etc. will always be a variable, and as one post put it, you might do 5 trips and average them together. But basically... running the same road, same direction, within a 60 minute period should be enough to get that data.

On another note.

Studies have shown that tonneau covers reduce aerodynamic drag. SEMA conducted a study in January 07′ that found tonneau covers reduce aerodynamic drag 4.2%-7.8%, depending upon speed.

Who knows that that 4.2%~7.8% figure actually translates to in 'real world' conditions, but it's a real figure. Think an open bed doesn't have drag? Check out a NASCAR truck and see what their wind tunnel test tell them about not having the beds covered. ;)

Of course at city driving speeds I doubt it'd ever be a measurable difference. But at 60 plus, I'm glad I have one.

Also glad I have that fancy air dam/valance as I'd also fall into the group that bought the truck BECAUSE it gets better mileage than some of the competition. Not to mention it just looks so darned good!

@Cato.....

I understand you don't like it on your truck, and that's great, GREAT looking truck, really nice indeed! But being lifted, offset wheels, flares, and big tires, your air dam/valance is the least of your MPG concerns.

I remember seeing somewhere where GM tested in the wind tunnel and the airstream hit the back of the tailgate. This is part of the reason that the tailgates now have built in "wings" in order to help the air to not break up. They also did the same testing with the tailgate down and you could see how much the lowered tailgate disrupted the air. With the factory rake in the truck I can't imagine a tonneau has any measurable effect. Now, with leveled trucks that would be a completely different story. I would also imagine that the cab/bed combination has an effect on this as well.

I can't imagine that the valence has any effect on a truck that's been lifted. I would assume that the lift causing more air to flow underneath the truck would cause for more lift and air disruption underneath the truck. I would say that once you lift all bets are off.

LTZDaddy · August 4, 2016

I remember seeing somewhere where GM tested in the wind tunnel and the airstream hit the back of the tailgate. This is part of the reason that the tailgates now have built in "wings" in order to help the air to not break up. They also did the same testing with the tailgate down and you could see how much the lowered tailgate disrupted the air. With the factory rake in the truck I can't imagine a tonneau has any measurable effect. Now, with leveled trucks that would be a completely different story. I would also imagine that the cab/bed combination has an effect on this as well.

I can't imagine that the valence has any effect on a truck that's been lifted. I would assume that the lift causing more air to flow underneath the truck would cause for more lift and air disruption underneath the truck. I would say that once you lift all bets are off.

I'm betting with the factory 'rake' the cover comes into play even more than when they are leveled. Think about it, on a cup car, getting the back end down just ¼" makes a huge difference in air hitting the spoiler. Same thing applies to these trucks, except the back end is a good 2½" higher than the front.

I'm also betting leaving the air dam/valence on a lifted truck still makes *some* difference. Although at that point there is SOOOOO much dirty air going underneath it'll be minimal at best. Reason it'd still work is because it's designed to channel air *around* the front of the truck, especially the outer lips that redirect the air and make a completely different stream around the front tires. Even lifted that effect would still come into play moving air towards the outside.

I was looking at how all that worked the other day actually. I have a couple of high velocity fans I use in the shop and had one out in the driveway while I was spraying water on the front of the truck and got to see how the valance was moving the air/water around the bumper, and towards the outside of the truck. That middle chrome piece in the bumper that has an integrated valance below is just as important as anything in that system as well.

Good to see the engineering that goes into these things work like it does these days. In my day we had big steel push bumpers, big steel step bumpers, monster Holley carbs and just let-er-rip! LOL