I dropped my tire pressure on my rear tires to 60psi weeks ago to try to improve my ride & my mpg's have been consistantly 1-2 mpg down from what I thought was going to be normal. I have less than 7K on my 2500 140 cargo, so I thought that my milage would improve some, but it hasn't. Just a coincidence that I happened to drop my tire pressure during this period?
Steve

 

Tire pressure does affect mpg, dropping the pressure will cause more tire on the pavement. Its just that much more harder to move that extra rubber on the road, so your engine works harder thus reducing your mpg. hope that helps

 

Thanks Shadowman,
I'll put the air back & see what happens. What year is your Shadow?
Steve

 

Your welcome. And my Shadow is a 1994. Last year production model. It is one of the last ones made. So I think that is pretty cool.

 

I do 60k plus miles a year with my 158" wb and I have always ran 60psi in the rear tires ever since noticing that the recommended rear tire pressure of 79psi tends to waer out the center of the tread faster than the rest of the tire. Or at least it does when you don't carry much wheight. I run the recommended psi in the front and 60psi in the rear and I seem to get the best tire wear. Right around six months of driving with the rear tires before they need replacing and about 8-9 months on the front. in the front I run Firestone transforce AT and BFGoodrich commercial traction in the rear. If you own an 03 this tire combo is OK since you can deactivate the traction control because the tires have slightly different diameters. Just my .02 about tires.

 

I have changed from air to Nitrogen gas in the tires. It cost $50 at dealer, but we use N2 at workand it is cheap to fill a bottle. Driving in extreme conditions as in mountains to desert I was getting trouble lights which indicate brake problems. It turns out the fluxtuation of pressure from altitude and temperature affects the sensors and the pressure and you can get that reading. The N2 is a harmless inert gas which maintains it pressure and cubic capacity under extreme condtions. No warning lights is better for the blood pressure and consistant tire pressure is a win for mileage too.
Jim

 

I keep 65lbs air pressure in my 3500 tires.

 

Generally anything that increases the 'flat spot'
at the spot where the tire tread meets the pavement
will hurt MPG
by increasing tire rolling resistance.

Deep tread depth where the rubber 'squishes' more
also hurts tire rolling resistance.

The way that this is taught in engineering classes
is first you teach the student that it takes more energy to climb a hill.

Then you teach the student that the flat spot at the bottom of the tire
is like constantly trying to climb a little hill. The 'grade' of a hill is treated exactly like the 'coefficient of tire rolling resistance' in the way that they take horsepower to overcome.

One last strange fact:
below the tire
the pavement ever so slightly depresses into a little rut.
Blacktop depresses into a deeper rut
than stiff concrete pavement.
Both blacktop and pavement depress less if the 'foundation' below them is well built, strong and hard.

The type of pavement you drive over also changes your MPG.
Blacktop is usually 1-2 MPG worse than concrete.
{hey...I hate concrete expansion joints too...but facts are facts}

more stuff along this line:

http://www.everytime.cummins.com/eve...Whitepaper.pdf