General lift question

[Gren71]

I upgraded from factory halogen to Oracle led driving lights in a Motobilt bumper.

Ahh gotcha

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[Gren71]

Mine lost an mpg, with a hard tonneau anyways. Myth busters did a test on it years ago and found it to be worse as well. I guess there could be a lot of factors though and different circumstances.

TLDR : Read the last two sentences

After your post i did a little googling and one of the articles i found actually referred to the mythbusters episode. The article makes the point that a LOT of engineering has gone into modern trucks in order to meet efficiency standards and the mythbusters findings aren’t necessarily applicable to newer trucks.

i then came across a study that was conducted where the main focus was to try and find a way to determine the causes of fuel inefficiency in vehicles, with the goal of increasing efficiency by %7 in order to reduce “greenhouse gasses”.

Unfortunately the sample size was very small and they didn’t have very many controls over their variables and their conclusion was… that they needed a larger sample size and to have more control over variables like driving habits.

but there was an interesting bit in there about the difference between older and newer vehicle aerodynamics that supported the first article that I read where they talked about the MythBusters episode.

All that said I think it’s really going to come down to anecdotal evidence for us with the tonneau cover. I’m in the camp of gaining miles per gallon, even with the hard trifold that I had originally. The added weight of a tonneau cover is negligible in the long run of your cargo carrying capacity so shouldn’t have a negative affect on your miles per gallon due to weight.

aerodynamics? I am by no means an expert but I would think covering the bed, or leaving it open, would both create the same vortex right behind the cab of the truck which would push air from over the roof towards the back of the vehicle without causing drag. The area where that vortex is created would just be smaller due to the tonneau cover, and maybe even more efficient because there’s less likelihood of excess air causing drag at the tailgate.

but again, I’m definitely not an expert in aerodynamics. And we all know that “the brick” was not designed for aerodynamics anyway!

 

[glassjawkid32]

TLDR : Read the last two sentences

After your post i did a little googling and one of the articles i found actually referred to the mythbusters episode. The article makes the point that a LOT of engineering has gone into modern trucks in order to meet efficiency standards and the mythbusters findings aren’t necessarily applicable to newer trucks.

i then came across a study that was conducted where the main focus was to try and find a way to determine the causes of fuel inefficiency in vehicles, with the goal of increasing efficiency by %7 in order to reduce “greenhouse gasses”.

Unfortunately the sample size was very small and they didn’t have very many controls over their variables and their conclusion was… that they needed a larger sample size and to have more control over variables like driving habits.

but there was an interesting bit in there about the difference between older and newer vehicle aerodynamics that supported the first article that I read where they talked about the MythBusters episode.

All that said I think it’s really going to come down to anecdotal evidence for us with the tonneau cover. I’m in the camp of gaining miles per gallon, even with the hard trifold that I had originally. The added weight of a tonneau cover is negligible in the long run of your cargo carrying capacity so shouldn’t have a negative affect on your miles per gallon due to weight.

TLDR : Read the last two sentences

After your post i did a little googling and one of the articles i found actually referred to the mythbusters episode. The article makes the point that a LOT of engineering has gone into modern trucks in order to meet efficiency standards and the mythbusters findings aren’t necessarily applicable to newer trucks.

i then came across a study that was conducted where the main focus was to try and find a way to determine the causes of fuel inefficiency in vehicles, with the goal of increasing efficiency by %7 in order to reduce “greenhouse gasses”.

Unfortunately the sample size was very small and they didn’t have very many controls over their variables and their conclusion was… that they needed a larger sample size and to have more control over variables like driving habits.

but there was an interesting bit in there about the difference between older and newer vehicle aerodynamics that supported the first article that I read where they talked about the MythBusters episode.

All that said I think it’s really going to come down to anecdotal evidence for us with the tonneau cover. I’m in the camp of gaining miles per gallon, even with the hard trifold that I had originally. The added weight of a tonneau cover is negligible in the long run of your cargo carrying capacity so shouldn’t have a negative affect on your miles per gallon due to weight.

aerodynamics? I am by no means an expert but I would think covering the bed, or leaving it open, would both create the same vortex right behind the cab of the truck which would push air from over the roof towards the back of the vehicle without causing drag. The area where that vortex is created would just be smaller due to the tonneau cover, and maybe even more efficient because there’s less likelihood of excess air causing drag at the tailgate.

but again, I’m definitely not an expert in aerodynamics. And we all know that “the brick” was not designed for aerodynamics anyway!

Yeah the added weight was the only thing I could imagine as the decrease in fuel economy happened directly after my tonneau install. I personally just don't believe it's a selling point for one, but rather a potential secondary benefit if anything.

 

[dcmdon]

Fuel economy is not entirely a function of drag. Your math is correct from a drag perspective but ignores all the other factors. So, the overall change will be less than 30%.

It will be a bit less because frictional losses (drivetrain, tires on the road) increase linearly with speed.

But at highway speeds 80% of the drag a car feels is aerodynamic. So by rounding down from 32% to 30% I get it about right. Its probably a bit less. but still close.

Edit - so I decided to run some numbers.

Lets assume that at 65 mph, 40 hp is used overcoming aerodynamic drag with 10hp in frictional losses.

Aerodynamic Drag
75/65 = 1.15, 1.15 squared = 1.32
1.32 x 40 = 53 hp

Rolling resistance
75/65 = 1.15
1.15 x 10 = 11.5 hp

Total drag
53+11.5 = 64.5 hp
64.5 / 50 = 1.29

So a 29% increase in overall drag and therefore about a 29% increase in fuel use doing the same drive at 75 mph vs 65 mph.

 

[Jocww]

I mean nascar trucks have bed covers...

 

[dcmdon]

I mean nascar trucks have bed covers...

I have no evidence to support this. But maybe the bed covers reduce lift even if they increase drag.

NASCAR is not concerned with this subtle aerodynamic change increasing speeds incrementally. One thing that I do know is that NASCAR is HUGELY interested in the trucks staying on the ground.

If the bed cover either reduces lift or moves the center of aerodynamic pressure towards the rear (which increases longitudinal stability) then its a good thing. Even if there is more drag.

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