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Old 10-03-2007, 05:37 PM   #1
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How much of an increase in mpg can I expect with overinflated tires?

For the first time ever I overinflated all four tires on my VX today. I put 45 psi in the front tires and 40 psi in the rear tires. I have always run 30 - 35 psi never going over 35.

Do the other overinflaters in this org have pre and post mpg data that shows let's say a 2 - 5 % increase? For my car that would translate to 1 to 2 extra mpg. I'm just asking because I will probably need to check tire pressure weekly to maintain the "high" pressure. I don't check nearly that often now.

I didn't notice any handling difference on dry pavement today at 60 mph. Cornering felt a little weird but it didn't feel unsafe.

My goal is to achieve 50 mpg average through a variety of techniques - this one being the first.
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Old 10-05-2007, 03:46 AM   #2
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*bump* anyone?

I was wondering too...
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Old 10-05-2007, 05:43 AM   #3
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It really depends on the type of tire,size and weight of the vehicle,type of surface among other items . I can assure you the gains can be/are quite good ,but only up to a certain point. I've been told that point is at the outskirts of Stoopidville,USA and happens to be where I reside.
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Old 10-05-2007, 06:47 AM   #4
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I think that perhaps the best way to answer that question is to break it down for what it is. It's a method of reducing rolling resistance. You can isolate it and measure that with a slow roll-down test. The big question, is how well you are able to take advantage of lower rolling resistance. At speed it won't make as much difference because of aero drag.

On a porker like mine, it really extends the coast and makes continual coasting on the slightest of grades possible - good thing too because it sucks more than enough gas going up these very slight grades.
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Old 10-05-2007, 08:01 AM   #5
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I run 50 psi in my tires that are rates for 35 psi and it drives beautifully. I cannot give you a hard figure on FE increase on that one because I did that together with installing LRR tires.

Last weekend however I drove my wife's car, a 2003 Buick LeSabre (yes, a big *** full size car), all the way up to Michigan and back, with my wife and kid in there as well and luggage in the trunk. My wife and her stepdad who the car originally belonged to, never got past 29 mpg on the highway which I thought was already good for a big car like that.

Before we left I increased the pressure from the 33 psi that was in there to around 52 (sidewall said 44 psi max). We then left for our trip. It has a computer in there that lets you see live mpg and average trip mpg. I drove close to 65, say 63/64 mph and got an average on a 200 mile trip of 37 mpg, with a Buick LeSabre!
It even surprised me! What can I attribute it to? Well, I drive pretty much with FE in mind but apart from not going fast i did not use any 'tricks' other than increase the tire pressure. So without even calculating it you can see what a difference the tire pressure can make.
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Old 10-06-2007, 10:58 AM   #6
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With my 2007 Toyota Yaris, the increase in MPG is 5% to 7% when I take my PSI to 50. The tires are rated for max of 44.

Now if your tires are very low (under specified psi) this can cause a loss of 10% or more off your MPG...this is really bad!
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Old 10-07-2007, 11:52 AM   #7
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I put my tires at 55 psi. At 55 psi, I "feel" I am probably getting 5%-10%. I felt that their was a significant increase in my EOC rolling distance, when I changed it to 55.

I had run 45 for a short period of time, but I didn't feel their was a significant increase in rolling distance, over 35 psi. After I moved it to 55, the increase was significant enough that I decided to quit fiddling with it and just leave it at 55 psi.

I figure with it that high, even if it loses a few pounds, it is still probably not going to be real significant, until I think to check them again.

I have probably put about 15,000 miles on my car, since I went to 55 psi and I haven't had any issues with blowouts, bad handling, or all of the other issues people are uncomfortable about. FWIW.
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Old 10-07-2007, 10:01 PM   #8
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Here are some easy rules about rolling resistance you can use to estimate the effects of pressure and other tire properties--

1. Rolling resistance is inversely proportional to tire pressure-- double the pressure, cut the rolling resistance in half. I WOULD NEVER RUN MY TIRE PRESSURE HIGHER THAN THE NUMBER ON THE SIDEWALL. The tire pressure that counts is the pressure while you are driving. Tire pressure goes up about one psi for each 10 degrees F in air temperature. Well-pressurized tires only run one or two degrees warmer than what they touch, but road surface can get very hot. I run my 44 psi tires at 40 psi and that works well for me.

2. Rolling resistance is inversely proportional to tire diameter. That number is published in tire catalogs. An additional benefit not related to rolling resistance is that the engine becomes more efficient at lower RPM, which you also get when you increase tire diameter. Watch out: when you put on larger-diameter tires, your guages will read differently and you can be fooled into thinking that your mileage is going down when it actually went up. And, careful about getting tickets with a lower-reading speedometer.

3. Low-profile tires will always get worse mileage than the high-profile types, that read /55 or higher. Sorry, no formula rule here. Tire width normally has no effect on mileage.

4. Rubber formulation is very important. Tires differ a lot in efficiency. Do your homework and buy the best tires. Check your mileage change with the new tires, and return them within 30 days for a refund if mileage goes down. (Be sure to ask about the 30 day guarantee when you buy, and you may want to keep your old tires just in case.)

Now, drive carefully-- improves car mileage, and yours too.

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Old 10-07-2007, 10:25 PM   #9
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Quote:
1. Rolling resistance is inversely proportional to tire pressure-- double the pressure, cut the rolling resistance in half. I WOULD NEVER RUN MY TIRE PRESSURE HIGHER THAN THE NUMBER ON THE SIDEWALL. The tire pressure that counts is the pressure while you are driving. Tire pressure goes up about one psi for each 10 degrees F in air temperature. Well-pressurized tires only run one or two degrees warmer than what they touch, but road surface can get very hot. I run my 44 psi tires at 40 psi and that works well for me.
This was posted in another thread...
http://www.officer.com/article/artic...on=19&id=27281

Of course, always go with what's good for you
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Old 10-07-2007, 11:01 PM   #10
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Quote:
3. Low-profile tires will always get worse mileage than the high-profile types, that read /55 or higher. Sorry, no formula rule here. Tire width normally has no effect on mileage.
Granted the tire size I run is much larger than the average vehicle, but the width of a tire does a play a part in gas mileage. Larger contact path vs a smaller narrower one.
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