[Thai]

Link: Debunking 7 fuel-economy myths - Yahoo! Autos

This is from Consumer Reports. The last point caught my eyes since i am a tire freak lately. So, i will likely get Conti EcoPlus next time around. But the other points are worth reading, like driving with windows open (thus, those window deflectors sure make sense now!) and no-name gas (esp. since i often use Chevron Fuel System cleaner every 5-10k miles anyways).

"Tires with low rolling resistance are always a smart choice

A lot of attention is paid to a tire’s rolling resistance, which is how much energy it takes to roll along. The lower the rolling resistance, the better your fuel economy will be. Maintaining the proper tire pressure will optimize the rolling resistance and real-world performance. Some tires gain low rolling resistance at the expense of wet-braking performance and tread life—a poor trade-off.

It’s better to look first for a tire that provides good all-around performance in important safety areas such as braking, handling, and hydroplaning resistance. Then use rolling resistance as the tiebreaker.

In our testing, we’ve found two all-season passenger-­car tires that deliver very good performance and low rolling resistance: the Continental ProContact EcoPlus+ and the Michelin Energy Saver A/S."

 

[Thai]

Note to Moderators...you can move this to General Discussion if you want....

 

[immortal_suby]

California passed laws for car and light truck and is working on implementing rolling resistance standards for commercial trucks. Many current tires don't meet that standard. I'd bet that other lawmakers will jump on the green bandwagon in the future.

It's not all about tread compound and grip. Inner tire construction is a large factor in rolling resistance. The tiremakers will be forced to find a way to improve without compromising safety. It's good to check out tirerack's reviews of overall performance and make an informed decision, as you have, when you try to improve fuel mileage.

 

[vr4Legacy]

I always thought the "fill up when it's cold" was a bunch of BS.

I tended to agree with the windows down hurts MPG until lately. I've tried my best to avoid AC just to see what effect it would have, and it seems my MPG are up 2-3 over a week in my Hyundai, which holds true. And there's nothing like some fresh air blowing through the cabin..

I've always been curiuos how much an "eco" tire really attributes. It's interesting to note that they didn't give any real numbers. The theory makes sense, but how much does it truly help in real life driving?

 

[plain OM]

Not sure about elsewhere, but in my neck of the woods, the gas station pumps actually monitor the temperature of the fuel being pumped and automatically adjust the volume delivered to 15 degrees C. So it doesn't matter when we fill up, or whether the ground temperature has changed, the amount we record, and pay for, is always the same. (The original idea was that we have to pay for the energy content, not the simple volume, and that takes car of the "myth".)

I've always been curiuos how much an "eco" tire really attributes. It's interesting to note that they didn't give any real numbers. The theory makes sense, but how much does it truly help in real life driving?

Yes, interesting that they didn't actually test the different tires for rolling resistance to see if the manufacturer claims can be substantiated. But then again, it's the myth that "tires with low rolling resistance are a good choice" that they are debunking.

I also found the comment about no-name gas interesting. It's true that the basic fuel is pretty much the same and the differences are in the additive package. By their own admission, the no-name might not have any additive package, so what about the "designed to clean the engine" that they do mention? Are the additives not effective?

Lots of gaps . . .

 

[Euchre]

This is a duplicate...
http://www.subaruoutback.org/forums/104-gen-4-2010-present/45881-fuel-economy-myths.html
(How many times can Yahoo regurgitate the SAME article?)

 

[Novablue]

100's of times.

Yahoo does this all the time which is one of the reason's they are not my home page anymore.

The part about 91 Gas is what I wish was out there more. Too many people who need to run 91 don't and several people upgrade "just because, it must be better" when there car doesn't need it.

 

[there4igraham]

This article typically shows up before summer and prior to Labor Day since more people are driving places and are likely to click on the article.

There's no substitute for driving responsibly. Accelerate leisurely, follow from an appropriate distance, don't accelerate towards stop lights, etc. If you find yourself at the head of the pack you're probably not driving responsibly. I used to win pretty much every stop light race until I started paying attention to the traffic behind me. Incredibly, they always caught up with me.

The AC myth goes both ways. If it's not too hot you should roll the windows down below 45 mph. On the freeway it's more economical to use the AC.

You should also make sure your tires (low rolling resistance or not) properly inflated.

 

[JoeCool]

my mileage went up from.....

I use only Michelin HydroEdge tires.....
I put 40 PSI in them for highway driving....
I can only fill up with gas when my engine is off as the pump nozzle keeps shutting off....
I use synthetic oil at the right weight......
take stuff out of your car that you don't need to reduce weight....
I get 30 MPG on the highway.....that's awesome considering how heavy these cars are.
I only use NGK Iridium plugs and man what a difference!

 

[uncljohn]

Mythbusters did the windows up vs. windows down and showed windows up w/ AC on was more economical on the highway. And I trust Mythbusters much more than Yahoo....

 

[Storkiln]

These efficiency principles are not demonstrated in clearer fashion than for anyone who has ridden a bicycle over a good distance. Because the rider is the power plant of that vehicle, a bike can acutely demonstrate the importance of efficiency. Tires that aren't properly inflated, chain not properly lubed, extra accessories attached to the bike that are just dead weight. These all manifest their presence by making life harder for the rider. I always say this as analogous to a car. Under-inflated tires, improper oil changes, and unnecessary cargo in the car all make the engine work that much harder. But instead of tiring out the rider, it just sucks more gas.

 

[Euchre]

Mythbusters did the windows up vs. windows down and showed windows up w/ AC on was more economical on the highway. And I trust Mythbusters much more than Yahoo....

I've seen that test. Do you call 45mph your highway speed? Not in my world. They seem to have chosen 45mph as an average of ALL driving speed, not 'highway'.

The story was actually written as part of Consumer Reports. I know, they're completely unscientific, right?

 

[AWDsome]

no one seems to even consider wind direction in the argument of windows up vs down. Driving into a headwind vs a tailwind can affect fuel economy 5 - 10% depending on how aerodynamic your car is. Subis aren't generally the greatest, typically being higher off the ground and often sporting roof racks.

To get to the point... If you're driving with a 10 or 15 mph tailwind, it'd then make more sense to keep the windows open even up to 55 or 60 mph. Turn that into a headwind, and you might consider rolling the windows up even around 40 mph. However, if you're in stop-and-go traffic, keeping the windows down may still prove more economical, since accelleration with the AC on saps so much power from the engine... especially on the smaller engines.

 

[Startiger]

Euche, If you notice the article says that CR didn't even test what the fuel economy was like with the windows down, so I would take that whole section with some massive salt. Not testing something is about as unscientific as you can get.

Mythbusters actually tested it twice. The second episode they measured both a several speeds, up to 65. Their results: below 50, windows down is better, above 50, AC has lower mileage.

If you think about it that is exactly what it should be. Windows down increases your air drag a lot. Drag is a function of speed squared. So while the effect is minimal at a low speed, the gets bigger bast. If you double your speed, it quadruples your drag.

AC is a constant load. At a low speed when the engine is not putting out much power, the AC load is a large hit on the mileage. As you go faster, your engine puts out more power and the percentage of the power produced that the AC uses drops. AC will be a smaller hit to mileage when you engine is putting out 120 HP vs when it is only putting out 50 HP.

So in the end, to cool a hot vehicle, windows down is best at low speeds, AC at high. The question is where will the cross over point be. it will vary for every vechle design. On average it is around 50, but YMMV.

 

[Looby]

Drag is a function of speed squared.

Drag force goes as speed squared, but drag power goes as speed cubed.
Doubling your speed requires 8x as much horsepower to overcome drag.

So, gallons/mile depends on speed^2; gallons/hour depends on speed^3.


...just picking a nit, I agree 100% with your overall analysis,

Looby
.