Over-Inflating the Tires

[SVOboy]

95 bucks seems like a lot. <a href=http://www.greenseal.org/recommendations/CGR_tire_rollingresistance.pdf target=_blank>This PDF<a/> <font color=black>says they should be a lot less. I looked for some on the place I bought my tires online (free shipping) and I didn't see any though, but I didn't look anywhere else cuz I should be working.
You're running the hx 14s with the, right?

[Matt Timion]

Originally Posted by SVOboy

95 bucks seems like a lot. <a href=http://www.greenseal.org/recommendations/CGR_tire_rollingresistance.pdf target=_blank>This PDF</a> <font color=black>says they should be a lot less. I looked for some on the place I bought my tires online (free shipping) and I didn't see any though, but I didn't look anywhere else cuz I should be working.
You're running the hx 14s with the, right?

Yeah, $95 seems like a lot to me too. I might check around (discount tire,etc.)

buying from Big-O makes sense though. They offer free rotation and balancing for the warranty of the tire (these ones are 60,000 miles). Getting your tires rotated and balances usually costs around $50 each time. Big-O also offers a free replacement. You don't get prorated like other tire places, you get a whole new tire for free if it is damaged, etc.

Anyway, I'm not sure the guy actually was showing me a LRR tire though, so i need to do some more research.

I am using HX 14 inch rims (or I WILL be using them). This means that I'll have to get 185x60R14 so my speedo doesn't get screwed up.

[kickflipjr]

I just bought some 195 60 15 tires for my saturn for $40 each. I know you can find civic tires for a similar price.

[Flatland2D]

This is the final trial I am doing for tire pressure. Sorry it took me a while to post my results.

<table border="5" cellpadding="5">
<tr>
<th colspan="2">
<b>10/2/05 - Tire Pressure Trial #4</b>
</th>
</tr>
<tr>
<td>Fuel economy:</td>
<td>34.0 mpg</td>
</tr>
<tr>
<td>Previous fuel economy:</td>
<td>34.7 mpg</td>
</tr>
<tr>
<td>Percent difference:</td>
<td>-2.02%</td>
</tr>
<tr>
<td>Trip:</td>
<td>132.1 miles</td>
</tr>
<tr>
<td>Fuel used:</td>
<td>3.885 gallons</td>
</tr>
<tr>
<td>Fuel grade:</td>
<td>Shell V-Power 93 octane</td>
</tr>
<tr>
<td>Driving type:</td>
<td>Highway</td>
</tr>
<tr>
<td>Target speed:</td>
<td>65 mph</td>
</tr><tr>
<td>Temperature:</td>
<td>80/78 degrees</td>
</tr>
</table>

Comments: The two temperatures are for the trip there and the trip back respectively. Fuel economy was right where I expected given the temperature I conducted the trial.

It does not appear that there is any substantial gain for my car by over inflating the tires. It is possible that the base MPG was off because I didn't have values over a range of temperatures. That is one thing I gain from all these trials for future tests. I know precisely how my car will run during different times in the day.

I have not fit my values to a curve yet, but I'm wondering if there should be some scaling factor to normalize fuel economy at a constant temperature. It's not possible for everybody to do their trials at the same temperature, but maybe we could come up with a method to calculate fuel economy at a standard temperature, like 72 degrees for example. That way our results will be easier to compare to each other and to our other trials if they were done at a different temperature.

Here's a summary of my trials for this experiment. Notice the strong correlation of temperature and fuel economy:
<table border="5" cellpadding="5">
<tr>
<th>Tire Pressure Experiment</th>
<th>Trial #1</th>
<th>Trial #2</th>
<th>Trial #3</th>
<th>Trial #4</th>
</tr>
<tr>
<td><b>Fuel Economy</b></td>
<td>35.0 mpg</td>
<td>33.8 mpg</td>
<td>37.0 mpg</td>
<td>34.0 mpg</td>
</tr>
<tr>
<td><b>Temperature</b></td>
<td>81 degrees</td>
<td>78 degrees</td>
<td>94 degrees</td>
<td>80/78 degrees</td>
</tr>
</table>

I obviously learned more about the effects of temperature than tire pressure, but that is even more valuable to know because it will effect every test we do. Ultimately tire pressure played very little into my results but I'll probably keep them around 40 psi anyway. I don't think there's any reason to go overboard with tire pressure in attempts to maximize fuel economy. Just keep them filled up to the recommended pressure and check them about every other tank.

[bagpipe goatee]

i just messed up my experiment, so i'll start over. I changed the oil, and it did have an effect on my gas mileage. darn.

[SVOboy]

What kind of oil to did change to and from? Was it a positive effect on the gas mileage?

[Compaq888]

My test results. My tire pressure before was 32F and 30R. I got 23.8-24.5mpg

I filled up the tires 37F and 35R and got 28.3-28.7mpg. The 27.4mpg is when I had 2 other people in the car and I was going 70mph.