Over-Inflating the Tires - Fuelly Forums

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Old 09-06-2005, 08:18 AM   #1
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Over-Inflating the Tires

So, here is the experiment: Putting more air in your tires than you are told by the manufacturer. This is pretty common, and unless you go crazy with it, not dangerous at all. In any case, the idea is this:

<strong>First: </strong>You figure out your average gas mileage and what PSI (pounds per square inch) your tires were running at.
<strong>Second: </strong>Pick another PSI somewhere higher that you would like to air up your tires to, and drive three tanks of gas and record you MPG each time by the standard fill-up and reset your trip odometer method.
<strong>Third: </strong>Figure out if there is any difference is fuel economy or handling and other such things. Then report it in this thread and I will crunch the numbers. After a sufficient amount of people report I should be able to come up with so solid numbers on the effects.

<strong>Note: </strong>Do not fill up your tires more than 10 PSI above the max. load printed on the tire. PSI should always be measured cold, that is also how the manufacturers so it (when the tire heats up it gets higher). Always fill up at the same pump and station, due to things like gas detergents and pump errors. Also check out this link given by chasgood about how to check tire pressure for more info on that:

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=1&currentpage=29

Here is the information you will need to report after your three tanks of driving:

PSI (before/after):
MPG (before/after):
Make/Model/Year:
Manufacturer and Type of Tire:
Size of Tire:
Tire Ratings:

Here is a sample (not my test):

PSI (before/after): 32/43
MPG (before/after): 42.9/45.6
Make/Model/Year: Honda/CRX/1991
Manufacturer and Type of Tire: Sumitomo All-Season
Size of Tire: 175/70/R13
Tire Ratings: A B 800

So there ya go, piece of cake. Just post up when you start so we'll know who is running it and then again when you're done and have results. Best way to submit the results is just to cut and paste the first little form thing and plug stuff in. Thanks.

PS: I start next fill up.
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Old 09-06-2005, 09:25 AM   #2
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If at all possible your base MPG should be based on 3 tanks of gas as well. It should go like this: 3 tanks of gas to get base MPG, then inflate tires, and then another 3 tanks of gas to get new MPG. This way we can measure even the smallest difference, and we don't have to rely on, "I get around 34ish miles per gallon."

exact is always better.
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Old 09-06-2005, 06:51 PM   #3
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We need to set up guide lines for checking air pressure. I suggest having a look at this link from a tire store as to how to check the pressure.
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=1&currentpage=29

Use the same tire pressure gauge for all testing. These things can varry + or - 1 psi.

The pressure sould be checked twice a week for these tests. Some tires loose air faster than others. Plus if there is a hot or cold weather spell the pressure will change.

Use the same gas pump and nozzle for all gas fills. Meters on pumps can varry up to a tenth of a gallon on a 5 gallon fill and still be legal.

If your car manual says the pressure front and back should be the same maybe try a third test with more air just in the front tires just to compare. Most FWD cars have 60% of the weight on the front wheels.
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Old 09-06-2005, 07:28 PM   #4
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Definately good suggestions, I think some of those things like same pumps are in Matt's general testing thing, but I dunno about the gauges, that is prolly a specific to this thing, so I will add it to the instructions up top, thanks.
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Old 09-06-2005, 07:42 PM   #5
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I totally forgot about gauges. Remember, the best way to determine if something acually affects mileage across cars is to keep as much the same as possible. It would be nice if we could all use the same meters, gas stations as each other. That would really solve a lot of error. Unfortunately we all live in different states.

I think a good digital pressure gauge would be wonderful for this experiment. if my car is up and running soon I'll be able to participate in this study.
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Old 09-10-2005, 06:47 PM   #6
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Okay, everyone who is interested now is the time to pipe up or ask questions in this thread of by messaging me on this site. I am about to start my official testing of tire inflation ripe and early monday morning! I will take befor and after pictures of my tires as well as stating before and after statistics to try and give a better idea of what is going on with the tire.

Quote:
A 10 percent reduction in rolling resistance would yield gas savings of 1 to 2 percent on average, according to Green Seal, a Washington-based nonprofit environmental advocacy organization.
We will be testing this principle to see the truth there. I'm hoping I can squeeze a few mpgs out of it at least, but that's what the test is for.
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Old 09-10-2005, 07:06 PM   #7
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I would love to participate in this study, but right now my car has mismatch tires on it. the rabbit has matching tires, but it needs a transmission and suspension, etc. so, do you think i should do it now, or wait till i have the rabbit together?
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Old 09-10-2005, 07:10 PM   #8
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Mismatched tires shouldn't make that much of a difference really I dun think. Just make sure to give the different ratings on the tires when you're done and then do it again when the rabbit is together. If the data with the mismatched tires doesn't fit a curve properly then it can always be thrown out, though I don't think it will create such a variation, however, in the interest of testing purity just report both types of tires and blah blah blah and we shall see if it works out crappily, though I doubt it, so go for it I think.
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Old 09-10-2005, 09:06 PM   #9
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Checking my tires tonight. Gasing up in the morning on the way to work. Set the pressure at 44/40 a few days ago. Will do the stock pressure after the over inflated test. Waiting on gas prices to go down to fill up and start the test. Good thing. Gas has gone down 20 cents in the last 4 days here.

So the testing begins.
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Old 09-10-2005, 09:32 PM   #10
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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.
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