MPG and Tire Pressure

In it's Shell !!!!!!

 

*hare

... And your post failed miserably.

 

You payed attention so that makes you the smart one.

 

*paid




I'm turning into a grammar cop like OZ.

 

File IFR

You are correct in that the ECU will compensate for thinner air by leaning out the fuel mixture to maintain a constant Stoichiometric balance, but what you are not accounting for is that you will be way down on power therefore you will need more fuel AND air to maintain the same speed as you would at sea level. If you run performance charts on ANY airplane you will see that FTC (fuel to climb) increases dramatically the higher your takeoff elevation is. That applies to turbine and Otto cycle engines.

 

I run 32 psi in my tires at all times if possible.
I get worse gas mileage in the mountain.
But I attribute it to the many incline I climb more than to the
air density.

But most likely it's due to using 4th gear. Over Drive shifts too much
so I drop it to 4 and roll on.

 

I'm in SE texas and run 47/45. Get pretty awesome mpg. The best thing to do is run a chalk test.

 

Yep, uphill you mash the gas to get going, and as soon as you back off the OD kicks in and you slow down. Mash the gas again and drop out of OD. Repeat. Or, you disable the OD which also has disadvantages.

Downhill is like freefall and you have to use your brakes too much.

Why I always buy manual transmissions.

 

You've summoned the OZ... He'll find you. Sneaky Canadians.

 

My experience has been the opposite - better mpg in the mountains, but probably a combination of factors - driving slower up hill, less a/c use, manual transmission, phase of the moon - who knows. But, on road trips, with a properly calibrated scangauge, I get about 15% better mpg (from 20 to 23) with my current truck, and similar increase with my previous truck.

 

I don't slow down in the mountains. I've seen them enough. I live in the foothill of the Smokey Mountains.
I maintain the speed limit and get to where I'm going.
Most of my travel is in 4th gear. I'd say at least 85% of it.

 

"Way down on power"? What do you mean.... considerable, extreme, dramatic?
A little? sure, but "way down"? Do you have any numbers to back it up instead of adjectives?

Not applicable here, sorry.

 

Good info here:

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=167

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=29

 

Let me throw some numbers at you. 03! 24! 13!

Seriously though, it's a few percent for every thousand feet of elevation. My Tacoma is probably about 35-45 HP lower here in CO than it would be at sea level. Not a huge deal. My mustang though is rocking about 150 hp lower here

As far as gas mileage is concerned, it's mostly a wash. If I had to pick one, I would say that the higher elevation gives you slightly better gas mileage.

 

Do I have numbers to back it up? Sure, I'll do a simple google search -

http://www.examiner.com/article/elevation-and-the-combustion-engine

A general rule of thumb is 3% power loss per 1,000 feet
If you are going from New Orleans to let's say Colorado, that's roughly 6,000 feet. That is a 18% power loss or 42.48 horsepower loss for the 4.0L Taco. I'd say that is way down...or "considerable, extreme, and dramatic".

One thing I will add is that because the air is less dense at altitude you also have less drag. As long as you don't work the engine any harder to compensate for lack of power you CAN increase your fuel mileage due to less air resistance.

What do you mean not applicable here?

 

There is no need to add that..... I've known that for a very long time.

 

Air current direction can make a big difference also.