Tire Pressure Cost me!

[BailOut]

Originally Posted by silver_vios

So if I run at 1 PSI I'll still get over 29 mpg? You can't use a straight line for an exponential curve.

Well said.

[Canuck]

Originally Posted by silver_vios

So if I run at 1 PSI I'll still get over 29 mpg? You can't use a straight line for an exponential curve.

I would hazard a guess that those figures hold true for the drivable range of pressures.

[sbergman27]

Originally Posted by silver_vios

So if I run at 1 PSI I'll still get over 29 mpg?

Don't be silly. The rule of thumb holds true for pressures reasonably near the placard pressure. That's the most useful part of the curve to target. And apparently the Goodyear researchers agree.

And it's likely (almost certainly) not exactly an exponential curve, but a more complex polynomial curve. (Homework: Explain polynomial curves of degree X to a family member, and then consider why Goodyear might have opted for a linear approximation to present to the public.) It is, however, probably close enough to an exponential curve (exponent < 1) to make a further observation. Going significantly *above* the placard pressure is likely to result in diminishing returns. The placard pressure is typically quite a bit higher than required by the load tables in order to get into a favorable part of the FE curve, where it makes sense to stop. People who air their tires far above the placard pressure, expecting to see substantial improvements, are thinking "linearly", and incorrectly. So thank you for making that observation.

-Steve

[Yaris Hilton]

http://opinionator.blogs.nytimes.com...8/power-tools/

[sbergman27]

Originally Posted by Yaris Hilton

http://opinionator.blogs.nytimes.com...8/power-tools/

Who'd have ever have expected to find the Mind of God in a giant wad of toilet paper...

[BailOut]

Math can be fun but whatever results one finds simply cannot undo reality. I coast farther and faster at 40 PSI than 32, at 50 PSI rather than 40, and at 60 PSI rather than 50. I do indeed see less of a gain from 50-60 versus 40-50, so there is the beginning of diminishing returns, but it is still enough of a gain to make it worthwhile.

[sbergman27]

Originally Posted by BailOut

I coast farther and faster at 40 PSI than 32, at 50 PSI rather than 40, and at 60 PSI rather than 50.

So you claim. Claims are a dime a gross on the Internet. Pick any notion you like, however absurd. Google for a bit, and you'll find someone fervently advocating that viewpoint. A lot of the time it is apparent that they really believe it.

I'll buy that it is possible to measure a difference in coasting distance at pressures beyond the placard pressure. Here's a fellow who went to the trouble of trying to quantify it: http://tinyurl.com/ylokr46

I've not seen convincing evidence of that translating into real, measurable, fuel economy gains which justify the additional safety risks. The potential reduction in rolling resistance of inflation past the placard pressures is modest. And tire rolling resistance represents a fraction of total resistance. Fuel economy has again become a popular topic of research in the last year or so. Show me a controlled study that supports your position.

-Steve

Edit:

Here is an interesting thread regarding pros, cons, risks: http://tinyurl.com/ykejamh

Poster "CapriRacer" is, in my opinion, the one to watch in that thread. He's careful about what he says, says precisely what he means, and is in a position to know.

[BailOut]

Originally Posted by sbergman27

Here is an interesting thread regarding pros, cons, risks: http://tinyurl.com/ykejamh

Please provide the full and real URL. I do not click on blind links, and neither should anyone else.

[Loren]

Originally Posted by BailOut

Please provide the full and real URL. I do not click on blind links, and neither should anyone else.

I've been meaning to comment on that, myself. I like to hover over a link and know where I'm going before I click it.

Steve, rather than TinyURLing everything, just use the URL tag on the forum. It allows you to display text and hide a lengthy URL behind it, but without completely obscuring it as a TinyURL does. Like This

This will also allow you to title your links, so you can say why you're linking it instead of just posting a list of blind links and assuming that we think so highly of you and have so much time on our hands that we're all just going to blindly click them.

In other words, if you tell us what the link is and we can see that it's a legitimate website link, it's a useful reference. If you don't tell us what it is and you hide it behind TinyURL, it's a "mystery link" that most people will ignore.

[sbergman27]

Originally Posted by BailOut

I do not click on blind links

Then feel free to stick your fingers in your ears and sing "La! La! La!" for as long as you want. It's a very interesting thread with lots of good information, BTW.

-Steve

[Rick]

Loren,

It's a good thread over on ecomodder.com. I agree, I would also like to know where it goes before I click but I'm not in mortal danger like windows users are.

Steve,

I'm running the OEM Goodyear Eagle LS tires at 50 psig and it works great. Exquisitely low RR, excellent cornering, and no uneven wear in 32k miles. The car pushed like a pig in the corners at 32 psig and got almost 5 less MPG in my driving circumstances. I make no claim about ANY other kind of tire and I guess I really don't care whether anyone else does likewise.

[Hershey]

of all the YARIS liftbacks we own or owned been able to average 36 m.p.g. overall with tires set at 34 > 36 . Can live with that . As for the sedan it's close to 38 m.p.g. overall for the past year and 10 months . That too is kept at 34 > 36 p.s.i.. Keep record of all fills .

[Falconeer]

umm what is Winter gas and Summer gas?? Some special fuel?

[BailOut]

Originally Posted by Falconeer

umm what is Winter gas and Summer gas?? Some special fuel?

Hi Falconeer,

Many areas of the U.S. use a different blend of gasoline in the cold months that burns cleaner but steals some of the caloric content of the plain version. This has an immediate and noticeable impact on MPG. When coupled with lower intake and ambient temps as well as wet/snowy/slushy roads it does a real job on pushing down one's winter mileage.

[Falconeer]

Thanks Brian!

[jhsouders]

Originally Posted by silver_vios

So if I run at 1 PSI I'll still get over 29 mpg? You can't use a straight line for an exponential curve.

You use this method of linear estimation in math, but its only used when the majority of all, in this example, all tire pressures will be within a given error amount.

[Zaphod]

Originally Posted by RedRide

I don't think so...
Let's not loose sight of the fact that "gas" is simply a by-product of refining oil.

If we stop using gas tomorrow, we would still need just as much oil for all the other products we get from oil from jet fuel/diesel fuel to plastics and everthing in between.
This a a littlt detail that the polititions always seem to conveniently forget.

Even in WWII we did not have a serious gas shortage. Gas was rationed mainly because the US government did not want people to wear out their tires as synthetic rubber was not yet fully developed and rubber was in short supply.

If there really was a legitimate means to stop using gas tomorrow via. a renewable resource, then it would indeed reduce the amount of oil we consume.

Of course a dramatic reduction in demand like that would reduce the price of oil, which would in turn attract new users to this cheap again energy resource and drive consumption back up in developing nations that could afford it.

Still, I think it shouldn't be denied that REDUCING our consumption of oil would have a positive effect on our national deficit and economy as a whole.

Just think ... one day historians are going to look back on the U.S. economy in bewilderment. Spending billions on a military effort to protect an economy that's almost entirely based on service, borrowing money to buy oil to move the products to locations that consumers have to borrow to even buy in the first place.

Not criticizing anyone driving their Yaris how they like ... just driving one for the daily commute instead of a 10mpg SUV is a huge improvement. But sarcasm regarding one's observations of loss in fuel economy as it's related to tire pressure on a Yaris fuel economy forum is a bit odd, don't you think?

[BailOut]

Well said, Zaphod.