Tire Pressure & Gas Mileage

[yoda]

Hi Everyone,

Well I've read (and even repeated it myself in posts) that it's important to keep the correct tire pressure for best mileage. I read somewhere that the recommended best pressure is 40 in the rears and 42 in the fronts...?

Anyway - I've had my car 2 months now and I finally got around to buying a tire guage and checking my pressure. Turns out the the pressure (to my surprise) is currently 33 in the rears and 34 in the fronts.

I'm gonna stop at a gas station tomorrow after work and get them up to 42 and 40.

I've been getting about 43mpg on my current tank (my mpg seems to get a little better with each tank) - I can't help wondering if it'll make a noticeable difference when I pressure-up the tires. I'm hoping for at least 1 or 2 mpg.

Any comments?

Thanks.

Yoda

[hdrygas]

Get one of those battery operated home pumps. Sunday is the day I check tire pressure. God helps those who help themselves.

[jayman]

Last year I tried playing with tire pressure after joining this forum, and concluded that in city driving there was no difference in MPG running the higher pressure.

At typical Trans Canada speeds of 100-110 km/h, usually there was no difference. A couple of times I appeared to gain around 2 MPG.

I also gained a rock hard ride, and with the roads the way they are around here, that is a good way to shake a car to pieces. I went back to 35F / 33R.

[dipper]

Well when I first picked up the Prius, I was getting only 42mpg on my work trips. A week later, checked the tires and found out that Dealer prep setup for 31psi all around. Adjusted to 36/34, the next week netted to 46mpg. Looks like having under-inflated tires are very BAD (less rolling resistance, I guess).

[KTPhil]

Break-in probably accounted for most of the gain.

[smtrader]

Here is my $.02 about the tire pressure deal. I was running on factory recommended pressure till I got on this forum. I thought 40ish was too extreme, so I went about half way...35 psi on all 4. My mileage went up slightly (1mpg-ish). I ran this way for about 6 months and basically forgot about it.

Then, about a month ago, took the car in to Firestone for an alignment and they reset my pressure to factory spec. Suddenly, my mileage is around 54! Best I've ever had. My driving habits have not changed, the alignment was not off, there is NOTHING that was different. The weather got a bit warmer but that's about it. I do mostly Southern Cal freeway driving to and from work, and I know traffic patterns haven't changed.

I'm riding on factory spec from now on! But...to each his own...

Brian

[jamarimutt]

I use 36/34. Above this the ride is too hard and the rattles are too loud.

[DaveinOlyWA]

<div class='quotetop'>QUOTE(smtrader\";p=\"97390)</div>

 I thought 40ish was too extreme, so I went about half way...35 psi on all 4.  
[/b]

for anyone thinking of not offseting pressure front to rear might want to consider that the lower pressure in the rear is because of the weight distribution in a stop creates a much lower coefficient of friction in the rear. this can cause you to spin in an emergency stop. the lower pressure in the rear is to create more stick to prevent this from happening. for safety conscious people if you have your fronts at 42 psi, your rears should be offset greater than the recommended 2 psi like 38 psi max.