slowcowboy wrote:on my ford explore on a 800 mile trip to rifle colorado and back to pavillon, wyoming I noticed no drop at all in gas milage towing my teardrop.
No lack of power and I towed 65 mph even up hills. I out ran larger motor homes and bumper pull rvs. same rigs known on here as ttt or standys.
I ran with no sway problems 65 in hard wind in wyoming and down around rifle last labor day.
I out ran my buddy towing a large boat with the same explore his is a 94 mine is a 95.
I make this trip to colorado every labor day and I go almost every year.
I have driven it with the same 95 ford explore about 5 to 6 times.
I got the same gas milage towing my teardrop last year as I got with out it the years before.
Slowcowboy.
JaggedEdges wrote:I have some experience with fluid dynamics also, and think it's likely that in some instances a low in height well formed teardrop could improve the overall aerodynamics of the combination. From skimming through, I'd give a kind of spitball of if your coefficient of drag is no less than about 0.4, your frontal area is no greater and the trailer is lower than the aerodynamically significant trailing edge of your vehicle, then you might have same mileage or even gain a tad. By a.s.t.e I mean where the bulk of the air departs the vehicle, for older trucks that may be the top of the cab, whereas with newer trucks it could be the top of the tailgate. For slippier sedans it would be rear edge of the trunk, but for some it might be at the roofline.
However, infernal combustion engines are stranger devices than most imagine, nothing is linear. Completely counter-intuitive is that your engine is not necessarily the most efficient at the speed where you get the best mpg, maybe for small 4 cyls, not so much for anything else. This is because efficiency, which is consumption per horsepower actually produced, and usually quoted technically as pounds of fuel per horsepower x hour, varies with load as well as engine speed. This is known as Brake Specific Fuel Consumption, if quoted as single figure it is peak value and not necessarily anywhere near peak output or peak torque.. https://en.wikipedia.org/wiki/Brake_spe ... onsumption
Now then, this can mean that a lightly loaded engine, like a big one, not pulling much, can be in a bad area for BSFC, only 30HP may be required to bowl it down the road, but maybe at this RPM and only 15% of it's rated output, it's sucking a particularly inefficient 0.6 pounds per HP x hour. Now if we place a higher demand on it 40HP, by dragging something, at the same speed, it might move into a more favorable area of the BSFC map, and only demand 0.45 pounds per HP x hour. So what is the fuel consumption per hour in the first and second case? Both identical, 18 pounds an hour, sorcery you say, no a direct consequence of the laws of thermodynamics as applied to internal combustion engines.
In the case of a smaller engine, it might already be near the best BSFC efficiency, it's more highly loaded, say 30% to produce the same output, now we might presume that in an "economy" car, the manufacturers have arranged this very thing, that at typical highway speeds it's in a good area on the BSFC map, by the design, valve timing and all other factors, with another passenger or two it might not change much, however, double it's load, by making it move twice as much, and it might scoot right over that good area of it's BSFC map and off the other side, resulting in higher specific fuel consumption per horsepower and getting very bad gas mileage overall.
However, this all jumps back to the aerodynamics again, the less change there is in that, the less change in load, with some outlier situations with lightly loaded large engines that there is wriggle room in the science to actually gain mpg with worse aero, and also lose mpg with better aero.
Weight tends to affect overall mpg less the longer your highway cruise is, because rolling resistance is most significant at lower speeds, and for of course, accelerating to higher speeds. At highways speeds it's dropped in significance to a few percent of total load. If total aero drag remained constant, the difference in load from weight and hence rolling resistance at speed between a regular car, and towing something half it's weight on another set of wheels, would typically be similar to having the A/C on or off.
Adirondackersouth wrote: I wonder if my Highlander is at optimum BSFC?
stevem50 wrote:the weight issue has been bouncing around in my head lately, more so as i read more about mike's giant foamy. i'm trying to shave lbs off my 4x10 woody to ease strain on my car climbing mountain roads. i'm only at 1100lbs fully loaded, but think how much better the mileage and performance if i could have another 2-300 lbs lighter...
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