How Various Practices Affect Car's Fuel Economy

It's nice to see this data.......... not really surprising considering that the wind tunnel tests are based around the design........ more than surprised though about the inefficiency drop of the vehicle with the windows down.

I break every rule because that is where the fun is.

If it tastes good or is fun......... It's bad for you.

So, does this mean that running the AC with all the windows up is more fuel efficient?

More so than running the AC with the windows down.

Since you break all the rules, do you run the AC with the windows down???????????

Actually, sometimes, yes, but the AC tends to cut into the horsepower, so I try to remember to shut it off.

I tend to run with the windows down as much as possible. If I had a convertible I would drop the top, too!

Hypermiling is not my cup of tea. I am okay that some people find that fun. However, to me, nothing competes to the sound of 8,000 rpm up an entrance ramp.

Has there ever been a study on the costs to all the drivers that didn't make it through the red light because the hypermiler wouldn't accelerate at a normal rate? There you and three or four others sit at the red light again burning fuel and going nowhere - how efficient is that?

Perhaps we should all start installing those 'push bumpers' like you see on some cop cars and tow trucks, you know the ones, those leaf spring loop things that let you creep up on another car and assist it forward.

That way everyone wins, Mr. Hypermiler gets to do his 'no gas' acceleration, we get through the intersection in time, and maybe Mr. Hypermiler will learn that it's not as much fun driving when you're being pushed down the road like a kid in a shopping cart.

I'm all for saving gas, but I'm also for driving to a destination in LESS time than it would take me to walk, not more.

Effective hypermiling does not preclude rapid acceleration, so long as that rapid acceleration doesn't just create something akin to the need to brake harder for the next light.

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Many automobile engines are at their most efficient just a little under WOT. Even though the fuel use during that time is high, the period of acceleration is much shorter than if you stretched the acceleration out by limiting yourself to quarter throttle. Having reached cruising speed more quickly than any car accelerating more slowly, the slower accelerating cars would need to travel at a higher speed, just to make the travel times the same...which is the only fair comparison...and since aerodynamic drag becomes an overriding concern at higher speed...and increases exponentially...the slower accelerating car gets further and further behind in the efficiency race.

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To answer your question though, I don't know if any studies have been done attempting to justify the anger towards those of us who attempt to time the lights to keep rolling, felt by people who race to brake from light to light, on the basis of fuel savings, but I suspect the outcome of any worthwhile study to that end would not justify that anger or abate it.

Timing the lights to keep rolling is fine, the hypermilers that piss everyone off are the ones who always go for the gentle slow accelerations, and starting to brake when they're still a block and a half from the light.Reaching a top speed of 5-10 UNDER the speed limit for the road, AND managing to get caught by a red light at Every. Single. Signaled. Intersection.

And the ones who do this during Rush Hour, which in Chicagoland runs from 7AM-10AM and 3PM-7PM when people are trying to get to work on time or get home so they can relax? Those people deserve to go to the Special Hell, the one reserved for child molesters and people who talk in movie theaters.

Well, if it is any consolation, they aren't saving much gas that way.

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It would be more appropriate to categorize those people as 'morons' rather than 'hypermilers'. With execution that bad, their original intent isn't critical.

That's nothing. I use the AC with the top down in the summertime.

'...The main takeaway from this study is that carrying excessive weight, be it by putting a cargo rack on a car's rooftop, or by towing a trailer, just like driving at higher speeds, always results in a decreased fuel economy.....'

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That is a pretty strange thing to suggest as the 'main takeaway', especially in light of mentioning;

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'....the Toyota Corolla's mileage was not affected by the cargo tray at all...'

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This seems to be a case of a special type of 'always' that happens to include 'not...at all'.

Actually the original report also includes "Driving with a rooftop cargo box decreased the Corolla's mileage even more, causing a drop of 22 percent, from 42.5 mpg at 60 mph to 33 mpg." so maybe the researchers could not read their own writing.

You are combining two paragraphs, one talking about a cargo BOX, the other abut a cargo TRAY.

A cargo box is an enclosed carrier, that has a set volume and drag 'envelope' regardless if it is empty or filled.

A cargo tray, on the other hand, is an open grille structure with a bottom and low sides, when empty it presents little surface area to produce drag, and if mounded close enough to the vehicles roof (which all depends on the level of compatibility between carrier and vehicle, some brands can mount closer than others, and a model designed by the same maker as the vehicle could be engineered to fit as close and snug as it it were a standard option for the car) might be able to sit in place without interfering with the vehicle aerodynamics.

With the remarkably small effect that the cargo TRAYS had, I would assume that they were tested empty, without any drag-producing cargo died down onto the tray.

Now here is a thing, I thought all vehicle drivers knew this information. I am surprised that they did not say that if you have a pick up truck, the fuel saving comes from dropping the tail gate, as in fully open. That save a lot of fuel.

The mod then is to remove the tail gate completely. A simple net holds any items inside the pick box and stops stuff falling out. Popular in Africa to see pick up trucks with no tail gate, to save fuel. Popular in Sweden too, to see dump trucks running with the tail gate fully opened and secured to the sides of the dump body when the body has no load. It cuts down a great deal of drag.

That is a long standing myth and leaving a gate down actually decrease mileage.

Even GM will tell you to leave the gate up as trucks are designed that way.

However, a tonneau will help, but a gate down does not and can actually cause aerodynamic lift of the rear at highway speeds - a bad thing for vehicle control of an empty truck.

If you believe different, just have a look at NASCAR truck racing. Tail up or down?

http://www.youtube.com/watch?v=r3aqHbD-O9E

Thanks.

Can't argue with that, though I am surprised. Thanks for this.

If memory serves, Mythbusters tackled this, and they found that the results wer as follows:

Best: Cargo Net

Tailgate Up

Tailgate Missing

Worst: Tailgate Down

With the tailgate up, you create a 'locked vortex,' the air behind the cab and in the bed circulate counter to the wheel rotation, and the aerodynamic effect is as if you have a hard shell from the top of the cab to the top of the tailgate.

The theory about the cargo net is that it creates a 'locked vortex' effect, but it tapers down closer to the bed, so the aerodynamic effect is even greater.

Tailgate missing does not create a locked vortex, so the turbulence behind the cap sucks your gas mileage down the tailpipe.

Tailgate down causes the same drag problems as tailgate missing, plus the handling problems from 'tail lift.'

I beleive we knew it, but not the actual numbers

I was on vacation the past two weeks, and I noticed on semi tractor trailers, I saw more trailers having adjustable fairings on the back. As well as fairings under the trailer, which I have been seeing more and more for the last couple of years.

http://www.atdynamics.com/aero.htm

"Popular in Africa to see pick up trucks with no tail gate, to save fuel. Popular in Sweden too, to see dump trucks running with the tail gate fully opened and secured to the sides of the dump body when the body has no load. It cuts down a great deal of drag."

"Popular wisdom" is not always correct, Here in the States, there used to be "Popular wisdom" about how the color of one's skin was linked to ones intelligence and ability, and there was also "Popular Wisdom" linking ones biologic gender to ability and competence. Science isn't about popularity and majority opinions, it's about facts and numbers.

Remember back when it was common to see trucks with chains hanging off the back, sparking ans skittering as they were dragged along the street? That was to prevent 'static electric buildup' that 'Popular Wisdom" said was a problem for Big Rigs. You don't see the chains anymore. Or remember the stickers at the gas stations that said cell phone use was dangerous around the pumps and could cause a fire? Those stickers now say it's dangerous to get into and out of the vehicle while fueling. That was pretty much due to researchers duplicating the 'cell phone gas station' myths tested by the Mythbusters and confirming that A) Cellphones do not produce enough of an electric potential to start a fire, and B) sliding synthetic fabrics over seat covers while entering or exiting a car CAN produce static charges that are hazardous around active fueling operations.

I think the greater danger is from the door switch, that turns the cabin lights on / off.

Is it possible that the spark can start a fire?

Never heard of any such fire, but can happen.

Um....no. Especially in nations which go below zero, the relative humidity is so low that sparks are formed by simply sliding across the seat, or pulling a coat (or jumper or sweater) off to cool down a bit. Static sparks resulted in my Corporal blowing the top off a fueling bowser (tender) and also blowing his face off at the same time. He now makes a living telling people about the dangers of static electricity, the ultimate point he makes is when he says nothing but takes his mask off.

Static is a serious force in Canada...beats the New Democratic Political Party in shear danger hands down!

Yes you are right. In India most places the humidity is high enough to prevent static buildup. Long time back on a visit to friends at Mississauga no one was willing to insert the key in the apartment lock as the passage had an acrylic carpet and the static shock was pretty bad.

We used to see chains hanging from tanker trucks, but not very common these days.

Make sure you discharge before refueling.

His was an unusual accident...everything was in place and should have worked. But the static still ignited the mostly empty space above the fuel. It does not happen that much (explosions that is) but when it does there are calls all over the place to have CO2 or nitrogen additive systems put into place. Thats what my corporal advocated over 40 years ago! Think it will happen?

That's actually pretty common. Had a 91 Chevrolet S10 and the with clothes seats that did that.

Close to every time I stepped out and touch the body of the truck, I got shocked.

" the ultimate point he makes is when he says nothing but takes his mask off."

Most people underestimate the effect of a Dramatic Reveal, but you can bet that when he does that little demonstration, the experience and the wisdom of 'static electricity is BAD' gets indelibly burned into the audiences brains.

.. If you'll pardon the unfortunate metaphor. I mean no disrespect to the unfortunate Corporal.

Or just stop driving the car in stop and go commuter traffic.

When it comes to *dynamics (aero or hydro), It. All. Depends. (I am not formally trained in the subject though.)

This becomes clear once one spends enough time trying to go fast without power (skiing, cycling, skating or even skydiving I guess), observing wind tunnel tests (either in a lab or on a TV ad), or merely looking at the aerodynamic designs of various vehicles. Just because something looks boxy or blobby doesn't mean it's not efficient.

The speed and fluid are the primary parameters of drag. A large frontal area may not be slow if you eliminate turbulence. That's why those slightly curved roof extenders on semi truck cabs help streamline the vehicle. You see it also in the trailer extension flaps now appearing.

My convertible's mileage hardly varies with the top up or down, if its real-time mpg readout can be trusted. A car can be designed to be efficient with the windows open, but it's much easier to make a streamlined design out of an enclosed cabin and the fashion is to use A/C most of the time anyway.

The non-aero parameters they played with are still completely relevant of course. But one of my favorite Mythbusters was when they added a ton of modeling clay to a Ford Taurus, dug dimples out of it, and thereby greatly improved the vehicle's mileage.

I almost laugh at some of these "Studies"

My daily beater, a 1983 Mercedes 300D Turbodiesel, averaged 32 MPG om a trip halfway across the country and back most of it averaging 80 mph, and as high as 90 mph for long stretches....not just once but two different times. And I kept records during the trip.

I'm lucky to get 26 on my average driving at much lower highway speeds, and thats been consistant over the 9 years I've been driving it.