I tell you, check your tire pressure

<div class='quotetop'>QUOTE(siliconhybrid @ Jun 21 2007, 02:56 PM) [snapback]465910[/snapback]</div>

That is an impressive increase. Time to check my tires B)

 

Tire rolling resistance is a particularly large slice of the 'energy pie' at low speeds. At higher speeds, suitable high inflation will help keep your tires cool and also help them to last longer. So, when going slow, it saves fuel money. Fast, it saves tire money. That's all I've got.

All Prius drivers ought to have an accurate pressure gauge and use it. A 12 volt plug-in air pump would not be a bad idea either. Find the maximum cold psi of your tires (printed on the sidewall), and work down from there as ride comfort dictates. Keeping the fronts 2 psi higher than the rears is a common suggestion. If this is not enough to keep your edge treads from wearing out faster, check the suspension alignment.

 

Don't forget that the new Prius has new tires, and they have to break in a bit, too, for the best MPG.

 

Increased tire pressure to 44/40 on my 07 with 5200 miles on the clock, still getting 44mpg even after hitting reset on the MFD. Not trying hard to drive like an old man either, and use AC more often than not. 44mpg is still great, but I wonder if the people getting 53mpg know something I don't know...

 

Yea, we don't use the AC. The AC literally kills the mileage man. I go from averaging 65 a tank without AC, to like 35 with AC.

 

<div class='quotetop'>QUOTE(siliconhybrid @ Jun 21 2007, 11:56 AM) [snapback]465910[/snapback]</div>

Having heard similar testimony from others in these forums, I bumped mine to 42 some time ago -- and haven't seen any significant increase... I guess it depends on your driving style, eh?

 

<div class='quotetop'>QUOTE(Mr. Zorg @ Jun 21 2007, 06:36 PM) [snapback]466085[/snapback]</div>

Driving style and conditions are a big factor. With so many variables it is impossible to attribute the effects to the causes. Driving in the low 90F temps in the evening can knock 2mpg off my current tank. I can get 1mpg back driving in the high 60F temps in the morning. Harder tires and a partially blocked grill help. With an almost 20mpg difference between "identical" cars (all Prius were hatchbacks) on the same route I still believe the driver makes the most difference.

Rank by mpg
mpg
M.M. Insight Hybrid 79.88
W. Phila. Attack Biodiesel 66.52
Hobbit Prius Hybrid 63.74
R. G. Jetta Diesel 62.03
W Phila. Jetta Biodiesel 59.30
N.H. Prius Hybrid 58.65
JimN Prius Hybrid 56.68
M.S. Insight Hybrid 54.94
E.K. Prius Hybrid 53.82
St Mark's Jetta Biodiesel 44.47
J.A. Prius Hybrid 44.23
T.H. Camry Gasoline 33.53


My interpretation of the results of
The Tour to the Shore 2007

 

There's just no physics to back up such a huge MPG increase from such modest pressure increases. Tire rolling resistance simply can't add (or subtract) that much from the equation. Not within those boundries!. If you'd gone from square to round tires we might have something.

But hey - If it is working for you, keep it up. Nothing to complain about if you can maintain that kind of mileage. Try going to 50PSI and see if you can get up into the 70's!

 

Using the Prius MPG simulator, increasing tire pressure in Goodyear Integritys from 38/36 to 44/42 raises MPG from 58.62 to 61.11 MPG at 55 MPH. At 35 MPH it goes from 82.12 to 86.76 MPG. This assumes the following:

Steady speed on level terrain
Smooth dry pavement
E10 fuel
80F ambient temp
No winds
300# load, occupants + cargo
No AC use

 

<div class='quotetop'>QUOTE(darelldd @ Jun 22 2007, 02:39 AM) [snapback]466243[/snapback]</div>

If there is an alignment problem, lower tire pressures will put more tire edge material in contact with the road and lead to higher drag. I used an IR thermometer to measure the tire tread temperature as a function of different pressures last fall when I knew I had a rear wheel alignment problem:



The right front tire had -0.86 degree camber versus the left front tire -0.53 degree. But I noticed that using max sidewall pressure changed the temperature profile and reduced the outer tread temperature. I used high tire pressure to mitigate an alignment problem until I could get the alignment fixed.

On my first tire rotation, the front tires were even at .53 both inner and outer for both front tires. However, one rear tire measured .77 and .78 giving some evidence to asymmetrical wear. Since I had received a shim kit, I also bought the "life-time alignment" service. I used this service to get a measure of which size shim provides what amount of correction. Now my rear tires are at -.08 and -.07 toe and -1.1 and -1.1 camber.

I still have an asymmetry on the front camber, -.50 and -1.0, and hopefully will get that corrected this weekend. Then I'll be ready to repeat the tire temperature profile test. BTW, I had some rolling resistance data pre-alignment but the results look "too good." I don't post data that I don't feel good about. Since I can install and take out the shims easily in the field, it is similar to changing a tire, I may do this just to find out.

Bob Wilson

 

Regardless of WHY you're getting the high numbers, the most important part here is that you ARE getting the high numbers. That's awesome. I run high pressure too (higher than you) but it is my technique that has the most impact on mileage. I can get 40 or I can get 55. I normally get 51-52 - you're doing better than I am, certainly. At least so far!

 

Checked my pressure today, all 4 are around 35PSI, but I just picked up the car on Wednesday, so they haven't broken in yet. Getting fairly decent mileage, its at 50MPG now (134miles on the car) But I also drive with AC CRANKED as its 108 today. I notices the worst mileage while going up the hills & accelerating. I still haven't managed the accelerating properly!