Over-Inflating the Tires

[Matt Timion]

Originally Posted by SVOboy

That's good to hear. I think I waited out at least 50 cents around my parts. Good to know we'll have at least three testers now, hope we can grab some more.

I'll be able to do this very soon, as soon as the wind stops and I can paint my car. this will be my first test for the group. After that I'll attempt to get the PCV catch can going, and then perhaps a few other tests like the K&N air filter and other small things.

Be sure to test tire pressure often, as air creeps out of the tires at a rather quick rate.

[SVOboy]

What happened to the 'tone? I thought it was gonna be your first testo?

[Matt Timion]

Originally Posted by SVOboy

What happened to the 'tone? I thought it was gonna be your first testo?

You're right... I totally forgot. I havn't had my coffee yet today.

[SVOboy]

First pictures of my tires for reference.

Before (35 psi):
<img src=http://www.filefarmer.com/cruisur/DSC02520.jpg>
After (45 psi):
<img src=http://www.filefarmer.com/cruisur/DSC02521.jpg>

It doesn't and didn't look like much of a difference. And the handling didn't seem to suffer. They are old busted *** tires anyway, I'm gonna order new ones soon and get them on in a few weeks. I went from 35 to 45 psi. The control mpg I am using is 41.5, cuz when I filled up this morning I got a miracle 45 mpg, haha, I am happy about that unless something got screwed up, but I think it is possible that I actually got that. Anyway, here starts the test. Three tanks. Everyone else who is working on this chime in!

[chasgood]

Still on my first tank. Noticed the car coasts better with the higher pressure.
The ride is a bit harsh. Feel small bumps and holes more. I can live with it.

[Flatland2D]

I've done my first highway test with 40psi all around. Here are the results:

<table border="5" cellpadding="5">
<tr>
<th colspan="2">
<b>9/21/05 - Tire Pressure Trial #1</b>
</th>
</tr>
<tr>
<td>Fuel economy:</td>
<td>35.0 mpg</td>
</tr>
<tr>
<td>Previous fuel economy:</td>
<td>34.7 mpg</td>
</tr>
<tr>
<td>Net gain:</td>
<td>0.3 mpg</td>
</tr>
<tr>
<td>Trip:</td>
<td>79.45 miles</td>
</tr>
<tr>
<td>Fuel used:</td>
<td>2.272 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>
</table>

Comments: I warmed up the tires for about 15 to 20 minutes before filling up with air. Tire pressures before and after listed below. The test went fine but when I went back to fill up, I had the early cut-off problem. I finally got the pump to stay on, but I can't be entirely certain it cut-off at the right time. It is in the ballpark of my previous test so that gives me some comfort in this method of measurement. I will conduct a second verification trial to try and confirm these results. So far it doesn't look like tire pressure plays a big role in my car. Even though the pressures were low, the tires were not saggy looking and didn't lift up much when filled up. Small bumps in the road respond sharper than before, but I also have an aftermarket suspension that makes the ride a little tighter anyway.

Another variable that should be held constant for all tests is fuel used during the test. Filling up on Shell one trial and Diamond Shamrock the next time could affect the results. If you absolutely have to switch, you should perform two more trials on the new gas to recalibrate your base mpg.

After one more trial of tire pressure I'm moving onto acetone. So far I've made two changes (PCV canister and tire pressure) and haven't seen any results. I'm eager to get some more mpg. I just hope my hydrogen generator doesn't flop, because right now that's what all my mpg dreams are built on.

<table border="5" cellpadding="5">
<tr>
<th>Tires</th>
<th>Before filling up</th>
<th>After filling up</th>
<th>After test</th>
</tr>
<tr>
<td>Front left:</td>
<td>27 psi</td>
<td>40 psi</td>
<td>40 psi</td>
</tr>
<tr>
<td>Front right:</td>
<td>26 psi</td>
<td>40 psi</td>
<td>40 psi</td>
</tr>
<tr>
<td>Rear left:</td>
<td>28 psi</td>
<td>40 psi</td>
<td>40 psi</td>
</tr>
<tr>
<td>Rear right:</td>
<td>28 psi</td>
<td>40 psi</td>
<td>40 psi</td>
</tr>
</table>

There is at least +/- 1psi of error in these measurements. I used the standard pencil gauge for checking pressure. As the results show, no rise/drop in pressure was noticed after test. I am led to believe the tires were sufficiently warmed up at the time I filled them up.

Addendum:
FYI for those participating in this experiment. I checked my tire pressure the other day. At night with the tires cool I measured 37 all around. The following day after driving around for a while with the outside temp 102, tire pressure was 41 all around. Temperature plays a big role in pressure, so drive around for a little and double check your pressure, then begin the trial.

[Flatland2D]

Here are the results of Tire Pressure Trial #2. Not exactly what I was expecting. There was a small drop in mpg measured. Not sure if there was error in the top-off method or other intangibles.

Tire pressure was checked before and after the trial. I had to add about 2 psi to each tire to get up to 40 psi. There was no change in pressure after the trial.

<table border="5" cellpadding="5">
<tr>
<th colspan="2">
<b>9/30/05 - Tire Pressure Trial #2</b>
</th>
</tr>
<tr>
<td>Fuel economy:</td>
<td>33.8 mpg</td>
</tr>
<tr>
<td>Previous fuel economy:</td>
<td>34.7 mpg</td>
</tr>
<tr>
<td>Percent difference:</td>
<td>-2.59%</td>
</tr>
<tr>
<td>Trip:</td>
<td>79.40 miles</td>
</tr>
<tr>
<td>Fuel used:</td>
<td>2.349 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>78 degrees</td>
</tr>
</table>

Comments: I'm not sure how to explain the drop in mpg after inflating the tires nearly 13psi. All I noticed tonight was that the winds picked up during the drive back. I could feel my car being blown around a little. It was a little colder since the last trial. That could have some effect.

As for the top-off method, I still think it's the most accurate way to measure mpg at this time (except for OBD2 + ScanGauge). I am referencing <a href="http://pesn.com/2005/03/25/6900071_Acura_Acetone/">Sterling D. Allen</a> at the PESWiki site and his results with this method. He got very consistent results which somewhat confirms the accuracy when topping off. He also noticed a slight change in mpg with a change in temperature.

I only planned on doing two trials for this experiment but I think I'm going to do one more just to see what happens before moving on to acetone. Hopefully it will be done in the next few days.

[Flatland2D]

So I have to admit, today's trial was really testing the spread in fuel economy at different temperatures.

<table border="5" cellpadding="5">
<tr>
<th colspan="2">
<b>10/1/05 - Tire Pressure Trial #3</b>
</th>
</tr>
<tr>
<td>Fuel economy:</td>
<td>37.0 mpg</td>
</tr>
<tr>
<td>Previous fuel economy:</td>
<td>34.7 mpg</td>
</tr>
<tr>
<td>Percent difference:</td>
<td>+6.63%</td>
</tr>
<tr>
<td>Trip:</td>
<td>85.10 miles</td>
</tr>
<tr>
<td>Fuel used:</td>
<td>2.302 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>94 degrees</td>
</tr>
</table>

Comments: That's a 3.2 mpg increase from last night's test. I was expecting to see some difference and that's why I decided to do this test today in the heat. Temperature was 16 degrees hotter than last night's test.

I hit a lot of red lights getting to the highway, which is about 3 miles from my gas station. It doesn't look like it screwed up things since my fuel economy went up.

I still had a full tank from topping off last night, so I drove around for about 10 miles to kill some gas. If gas volume does change with temperature, I wanted to eliminate that as a variable. Fuel economy for those 10 miles was calculated at about 26 mpg, about what it should be for city driving.

I don't plan on doing another test in the daytime because I was dripping sweat during this trial. I had to keep everything else constant, which means no A/C and windows up. It's all in the name of science though, so I'm ok with that. My other trials were all done around midnight so heat is not an issue. Outside temperature is more constant at this time anyway so that should partially eliminate it as a variable. At least today I could enjoy the drive through the beautiful Texas hill country though.

I missed my usual turn-around exit, so this trial went a littler further than the others.

One thing I haven't mentioned is that I always have my stereo system on pretty loud during the trial. It helps the time go by faster. As long as I do this for every test it shouldn't introduce error. I don't think eletrical load would play a huge role in fuel economy anyway. I overheated my amp today and in trial #1. It's rated for 300W which is a little too small for the rest of my system.

I'll be travelling about 130 miles tomorrow, almost all highway and 65 mph except for a small stretch of 55 mph. I'll use this as my last and final trial for tire pressure. I'll leave in the morning and return in the evening, so hopefully temperature will be about the same both ways. After tomorrow, it's all acetone.

[squala]

Here are some pros and cons of different tire pressure settings.

Low

+ better handling
+ less chances of getting a puncture
- outer parts of tire wear out more easily

High

+ less rolling resistance
+ better fuel economy
- middle part of tire wears out more easily

Keep in mind that we also spend money on tires, not just fuel. It's important to make them last as long as possible in order to save.

[Matt Timion]

Originally Posted by squala

Here are some pros and cons of different tire pressure settings.

Low

+ better handling
+ less chances of getting a puncture
- outer parts of tire wear out more easily

High

+ less rolling resistance
+ better fuel economy
- middle part of tire wears out more easily

Keep in mind that we also spend money on tires, not just fuel. It's important to make them last as long as possible in order to save.

These are all things I've thought about recently. I was quoted $95 per tire for good LRR tires at Big-O. I might try somewhere else. Quite honestly, if I end up paying $95 per tire, there is no way I'll over-inflate them. I do'nt need the center wearing out any faster than normal. I'd rather just check every week and keep them at max PSI.