Thoughts on Fuel Economy:How to Stretch a Gallon of Gasoline

I'm confused

Isn't that the one thing we DO have control over?

 

<div class='quotetop'>QUOTE(MikeSF @ Nov 27 2007, 04:07 PM) [snapback]544897[/snapback]</div>

I think he meant "the one thing they have no control over".

 

One thing that has always irritated me since I've been driving. And I don't know if this is true of older Toyota's as the prius is my first and the only Toyota I've ever driven, but many lower priced cars that were in my price range back in the 90's (sub $18,000 range) still only had 3 speed automatics. Seems like such a waste that the engineers did to save the company a few dollars which is one reason why I chose my 5 speed Manual back then. Now that times have changed just about all of the "Crossover" and "SUV" vehicles are coming with 5 speed automatics so that they get more reasonable fuel economy. This is how a larger vehicle like the Ford Edge manages to get an EPA highway rating of 29MPG. <-- which is practically as good as most midsize cars.

 

Heck my first car, an 83 toyota corolla only had one side mirror! how much cheaper could you get for trying to cut costs!

 

All in all... a good article.

But...

As usual many of us will take issue with some of the author's assertions. For instance just to pick one: Tire pressure and the consequences of running the tires inflated above the sidewall max. He claims that tires are likely to wear more aggressively in the middle (or suffer premature wear).

There are a few other out-of-date or simply exaggerated claims but heck... we're kind of used to it.


Cheers;

MSantos

 

good points. Everyone should take responsibility for any modification they do, good or bad.

I drive smart and get 55-85 in a car pool with 3 of us. That's even better than hypermiling by carring more people. Then when you drive for top miles you all do even better.

I also stay on local roads instead of highways. It's easier to get high mpg and safer. Speed does kill, 40,000 or more a year from vehicles. A little slower is much safer and less wind resistance.

 

When you overinflate tires you are creating higher heat inside the tire which could result in a tire failure which could result in an accident.

Also over inflated tires do not grip the road as well bcus the contact patch is now smaller which means your car will handle worse and have less effective brakes which could also cause an accident

 

Are you sure about that? Most of the heat should be generated by the friction between the tire and the road surface. Higher pressure in the tire shouldn't be affected by this. In other words, the pressure will still increase in a linear fashion with Temperature (assuming the gas in the tire follows the ideal gas law).

PV = nRT where P = Pressure and T = Temperature and n = # of moles of gas. If we assume V (volume) and R (the gas constant) to be constants <e.g. they don't change.....>

we get P = nT. We've added more moles of gas (higher pressure) thus the pressure went up. At this point n is now a constant.

Thus P = T. As the temperature increases, the Pressure increases. Increasing the temperature will not increase the # of moles of gas (air) in the tires, thus justifying our assumption that it is a constant.

You will have less "grip" on the road because the patch of contact is less (agreed) but you will also have a lower rolling resistance thus higher gas mileage (as you won't need as much energy to overcome the rolling resistance).

 

I read this yesterday: Hybrids: Seven worries, seven answers

This quote caught my eye: You could save more by simply accelerating and braking more gently in your current vehicle. (than "just drive it")

Explanation: Someone has a Toyota Camry and drive it like the typical driver (speed limit + 10mph, etc). Going the speed limit and going easy on the brakes and accelerator will save more gas than getting the hybrid Camry, although both will make substantial impacts.

 

Math was never my strong suit so I'm still recovering from your formulas

but wont the heat from the contact patch eventually transfer to the air inside the tire thus increasing the pressure even higher and making it that much more likely that the tire will fail when it was laready Over the manufacturers rating at the begining ?

 

Buying a used diesel Jetta will also do a lot more towards helping the environment than buying any new car

 

Sorry, wrong. You generate LESS heat in a better-inflated tire
when it's rolling. Unless you're layin' rubber all over town,
heat is not generated by the contact patch, it's generated by
flexing *around* it particularly in the sidewalls. Minimize
that by running 'em harder, and you wind up with COOLER tires,
firmer handling, SHORTER stopping distances and better traction,
etc etc. Read this. The whole "soft for more traction" myth is
total crap in every situation except soft sand or dirt where you
actually need to spread out the footprint a little.
.
Sorry for the abruptness, but we really need to NOT spread
incorrect information.
.
_H*

 

Well, I have a Prius and a Diesel Jetta. Here is my observation on "cleanliness".

1) I can't start the Jetta in the garage if I am facing out. Even with the garage open, it spews toxic exhaust all over the place. It is a major disadvantage. Not a problem with the Prius. So if you relate that to what is going into the air the Prius is much cleaner.

2) Vehicle washing. The Jetta requires the rear of the vehicle to be washed at least once a month. The reason is, soot from the exhaust deposits on the rear of the car. It gets caked on the paint and bumper. I'm sure you have seem this on any number of diesels. It is worse right around the exhaust but really covers the whole back of the car to some extent. The Prius does not have this problem. What comes out of the eshaust of the Prius is much cleaner.

3) Oil. I like to do my oil changes. I don't know why I just do. The Jetta oil is much dirtier than the Prius oil. This oil has to go somewhere. If it is not recycled it goes to the environment. The Prius oil is much cleaner at oil change time.

4) Brake dust. The Jetta wheels require cleaning every month. If I don't, then the brake dust gets caked on and is difficult to clean. The Prius hasn't needed its wheels cleaned for brake dust since I have had the car. The Prius is much cleaner.

These are just my personal observations. I don't know about manufacture, batteries and the like as they relate to the environment. I really like the jetta and I am not knocking it at all. It is my wife's primary car and the car we take on trips. I also really like the Prius. It is my primary car.

The Prius is just a cleaner car. This has to relate somehow to a cleaner environment when you figure there well are over 200,000 Prii on the highways.

 

Slightly off-topic ....That was an interesting article. I did notice in point 4 ("justify the premium") that the author mentioned "fast depreciation" (and the later point 6 about resale value). Is there any solid evidence for this assertion? Do Prii really depreciate at a faster rate than non-hybrid (or hell, even other hybrid) cars? Sorry if this has been discussed and debunked before. It's getting annoying seeing that in articles and floating around as "common knowledge". If there are significant data and or wide enough experiences from private sellers to back that claim up that's one thing, but right now it really strikes me as another "CNW/Hummer" runaway urban legend.

 

Yes, when you compress a gas, it gets hot. But only until the heat conducts out into the enviorment. Which is like maybe 1/2 hour. Then the air in the tire has the same temp as the air outside the tire. At least until you start to drive.

With regards to the Prius tire pressures, its well documented here that a Prius with the 15 inch tires will burn through the outside edges of the tires in as little as 20 K miles when inflated to the door panel values. And these are 40 K mile rated tires. This means that the center of the patch is not at the same road contact pressure as the outer rings of the patch as the two zones wear differently. Inflating the tires to 42/40 greatly improves the tire wear pattern, and thus indicates that the center of the patch is more properly loaded.

When a tire rotates, the sidewalls flex. If there is higher air-pressure in the tire, the flex is less. With less flex, there is less heat disipated in the sidewall. And better mileage. Take a piece of rubber and flex it over and over. Now feel the area where the bending occured. It will be warm.

 

Hi Morpheusx,

MB even has a station wagon with a 7 speed automatic tranny!

http://www.mbusa.com/models/main.do?modelCode=R350V4