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Quick question, what is this?


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#11 ski3pin

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Posted 15 March 2012 - 02:03 PM

Highz, thanks for the explanation! Science! :)
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#12 highz

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Posted 15 March 2012 - 07:07 PM

When I put my camper on my truck the mileage dropped from 14 to 12mpg. Without any real facts or knowledge my gut feel was that this drop was due to increased air drag rather than the increased weight.
This seems like such a basic/obvious question that it must have been answered before, if not on this site then on some truck or other camper site.

I bet one or more of the more truck-y guys on WTW already know...or have a definite opinion, at least. ;)


Hey, Mark. The Eagle on the Ranger dropped my mileage from 20 to 18 mpg (low speed driving). I found this link about how extra weight affects mileage:

http://www.fuelecono...l#remove-weight

One to two percent per 100 lbs. That's agrees with the mpg drop we see.
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#13 chnlisle

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Posted 15 March 2012 - 07:11 PM

Hey, Mark. The Eagle on the Ranger dropped my mileage from 20 to 18 mpg (low speed driving). I found this link about how extra weight affects mileage:

http://www.fuelecono...l#remove-weight

One to two percent per 100 lbs. That's agrees with the mpg drop we see.

That has always been my guess as well. Fuel economy is more tied to what your hauling and how hard the truck has to work to get there. When I had the camper on my T-100 the milage went from 18mpg to 15mpg. On the Ram CTD I really don't notice any change in fuel economy. Still if a fairing would deliver some sort of substantial savings I'd be interested.
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#14 highz

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Posted 15 March 2012 - 07:28 PM

That has always been my guess as well. Fuel economy is more tied to what your hauling and how hard the truck has to work to get there. When I had the camper on my T-100 the milage went from 18mpg to 15mpg. On the Ram CTD I really don't notice any change in fuel economy. Still if a fairing would deliver some sort of substantial savings I'd be interested.


Right. I agree with what you say. I see the ten percent drop in mpg at low to moderate speeds, but see worse mileage when I am forced to take the interstate. That is where aerodynamic drag really starts to kick in (or in a strong headwind). Since I prefer low speed roads away from cities, I can usually minimize the aerodynamic drag effect. I haven't felt the need to modify my rig with a fairing yet. If I had to drive a lot of high speed roads, I might change my mind - for a quieter ride, if nothing else.
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#15 ski3pin

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Posted 15 March 2012 - 08:43 PM

Right. I agree with what you say. I see the ten percent drop in mpg at low to moderate speeds, but see worse mileage when I am forced to take the interstate. That is where aerodynamic drag really starts to kick in (or in a strong headwind). Since I prefer low speed roads away from cities, I can usually minimize the aerodynamic drag effect. I haven't felt the need to modify my rig with a fairing yet. If I had to drive a lot of high speed roads, I might change my mind - for a quieter ride, if nothing else.


This has been my experience also. I really notice a difference driving above 60 mph or dealing with a strong wind.
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#16 SunMan

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Posted 15 March 2012 - 10:03 PM

This has been my experience also. I really notice a difference driving above 60 mph or dealing with a strong wind.


My Scanguage seems to support this. The faster I go (above 65ish) the lower my realtime MPG is and I can feel the resistance more. When i'm really pushing it is awful to watch, really makes you factor the value of time vs. $ in your driving.
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#17 MarkBC

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Posted 15 March 2012 - 10:05 PM

I see that the weight effect -- 1-2%/100lbs -- would matter if you were accelerating or climbing (which, as Einstein taught us, is ~ the same thing; Who knew that you'd need General Relativity to explain our truck's gas mileage! Posted Image). But for those long stretches on cruise control -- driving I-5 between Redding and Bakersfield (my condolences to anyone who does that Posted Image) or on I-70 between Denver and Kansas City (never done it but it can't be much fun, either) -- seems like weight can't matter much, or at all.

Like some of you, I agree about the wind-drag cost of driving fast -- I don't want to pay that cost either, which is why I'm usually in the right lane when driving on rural interstates in NV or UT. In Oregon we're not allowed to drive faster than 55 except on Interstate Freeways, and then the max is only 65. (That may be for the same reason that we're not allowed to pump our own gas: Assisted suicide is legal in Oregon, and we're not going to squander that right by dying prematurely in a horrible accident. Well, that's one theory... Posted Image).
When driving I-80 across northern Nevada where the speed limit is 75mph I keep it close to 65 -- never above 70, though many are exceeding 80mph. When I'm only getting 12mpg at best, I am just too thrifty to want to spend even more on gas just to cut my driving time by 10 or 15% -- not worth it to me. And then there's the Planet to consider... (though if that was really a priority I wouldn't go on out-of-town camping trips at all, would I?)

Or that's the way I see it. Posted Image
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#18 EdoHart

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Posted 16 March 2012 - 01:57 AM

I see that the weight effect -- 1-2%/100lbs -- would matter if you were accelerating or climbing (which, as Einstein taught us, is ~ the same thing; Who knew that you'd need General Relativity to explain our truck's gas mileage! Posted Image). But for those long stretches on cruise control -- driving I-5 between Redding and Bakersfield (my condolences to anyone who does that Posted Image) or on I-70 between Denver and Kansas City (never done it but it can't be much fun, either) -- seems like weight can't matter much, or at all.

Like some of you, I agree about the wind-drag cost of driving fast -- and I don't want to pay it either, which is why I'm usually in the right lane when driving on rural interstates in NV or UT. In Oregon we're not allowed to drive faster than 55 except on Interstate Freeways, and then the max is only 65. (That may be for the same reason that we're not allowed to pump our own gas: Assisted suicide is legal in Oregon, and we're not going to squander that right by dying prematurely in a horrible accident. Well, that's one theory... Posted Image).
When driving I-80 across northern Nevada where the speed limit is 75mph I keep it close to 65 -- never above 70, though many are exceeding 80mph. When I'm only getting 12mpg at best, I am just too thrifty to want to spend even more on gas just to cut my driving time by 10 or 15% -- not worth it to me. And then there's the Planet to consider... (though if that was really a priority I wouldn't go on out-of-town camping trips at all, would I?)

Or that's the way I see it. Posted Image


I think you mean Newton. Anyway...
I don't remember Newton's laws of physics by their numbers, but IIRC
Law 1 is: An object at rest tends to stay at rest, and an object in motion tends to stay in motion provided that no external force is appplied.

Let us remember that weight (pounds) is a measure of force. Also, force can be applied in any direction. Force which pushes us forward is often called thrust, and force which retards us is often called drag.

The more a vehicle weighs, the more force it applies to it's wheel bearings and tires, which means more drag, thus one needs to apply more thrust to maintain a constant speed.
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#19 MarkBC

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Posted 16 March 2012 - 02:53 AM

I think you mean Newton.

No, I meant Einstein. I was referring to the equivalence of acceleration and gravity (where I said "accelerating or climbing"). See here, for example.
Newton quantified the effect of gravity (pretty close), but he didn't understand it.

The more a vehicle weighs, the more force it applies to it's wheel bearings and tires, which means more drag, thus one needs to apply more thrust to maintain a constant speed.

This must be an effect too...but I bet the acceleration in normal driving (that is, not cross-flat-country on cruise control) would be a major effect, since accelerating more weight (mass) requires more energy which means more fuel. And people accelerate every time they start from a stop or regain their target speed after slowing down.
I don't have any quantitative facts to back this up -- I'm just making it up, gut feel...and it's an engineer/scientist gut, not an auto/truck-guy gut, so my gut may not apply. Posted Image I feel more sure in saying that the relative effect of vehicle weight on mechanical drag would vary depending on the vehicle...

...Just as the effect of wind-drag varies with different vehicles: I know wind is a bigger drag -- requiring a greater %-increase in fuel to overcome -- on my F250-with-camper than on my Honda Civic sedan. That big square back of the camper-pickup is just asking for a storm of drag-producing turbulence!
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#20 EdoHart

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Posted 16 March 2012 - 04:07 AM

No, I meant Einstein. I was referring to the equivalence of acceleration and gravity (where I said "accelerating or climbing"). See here, for example.
Newton quantified the effect of gravity (pretty close), but he didn't understand it.


This must be an effect too...but I bet the acceleration in normal driving (that is, not cross-flat-country on cruise control) would be a major effect, since accelerating more weight (mass) requires more energy which means more fuel. And people accelerate every time they start from a stop or regain their target speed after slowing down.
I don't have any quantitative facts to back this up -- I'm just making it up, gut feel...and it's an engineer/scientist gut, not an auto/truck-guy gut, so my gut may not apply. Posted Image I feel more sure in saying that the relative effect of vehicle weight on mechanical drag would vary depending on the vehicle...

...Just as the effect of wind-drag varies with different vehicles: I know wind is a bigger drag -- requiring a greater %-increase in fuel to overcome -- on my F250-with-camper than on my Honda Civic sedan. That big square back of the camper-pickup is just asking for a storm of drag-producing turbulence!

I love this stuff. Keep it coming.Posted Image Maybe as member administrator you can spin this off to another thread?

I remember reading that the only way to describe the orbit of Mercury was to include Einstein's General Theory of Relatviity. I can explain Einstein's general theory and special theory of relativity in layman's terms, but I don't comprehend either in the slightest.

Newton observed and predicted the effects of gravity in a Newtoniun Universe.
Einstein observed and predicted the effectis of gravity in an Einsteinian Universe.

Both were correct, yet neither desciibed gravity. Posted Image
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