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Thread: MPG while cruising without hurry

  1. #11
    Here's some more - I've done a couple of tests comparing coastdown distances at various tire pressures, including with RE92's - same size & LRR like the Enasaves:

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    from: https://ecomodder.com/forum/showthre...tire-2721.html

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    from: https://ecomodder.com/forum/showthre...tire-2721.html


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        click to view fuel log View my fuel log 2014 Mirage ES 1.2 manual: 63.2 mpg (US) ... 26.9 km/L ... 3.7 L/100 km ... 75.9 mpg (Imp)


  2. #12
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    Quote Originally Posted by Loren View Post
    It has been proven.

    As I recall, it has to do with two things. 1. more pressure keeps the tire rounder, so that it's not constantly flexing the sidewalls and creating heat. (this is much of the principle of how LRR tires work) 2. you reach a point where you start crowning the tread and decreasing the contact patch.

    It's not great for a lot of other things, but it absolutely increases MPG!

    https://ecomodder.com/forum/showthre...ure-17151.html
    Control, 35psi (manufacturer recomendation)
    tyres at 10psi = 3.7% increase in consumption
    tyres at 30psi = 1.2% increase in consumption
    tyres at 40psi = 6.2% decrease in consumption
    tyres at 60psi = 7.6% decrease in consumption

    Those numbers don't prove much of a gain. A tire at 40 psi is probably not at the maximum psi rating of the tire. What is gained if the tire is inflated to the maximum rating of 44 psi verses an over inflated tire?

    If we are talking about a tire rated @ 44 maximum psi tire inflated to 44 psi (not over inflated), the gain of going above that would be what? Maybe 1%. From the data share above I wouldn't estimate any more than that.

    Looking at Metro's data below - a 50 psi tire did better than the 55 psi tire. How does that happen?

    I never run my tires @ manufacturer recommended psi, but I do stay below the maximum psi rating of the tire.

    When it's 90F plus in the summer & Eggman has just traveled a good distance in his Mirage, I would like him to pull out a tire gauge & share the psi of his tires at that moment. I sincerely hope he does that for us some day this summer.

    A somewhat lame study I have read on this was done by Popular Mechanics. They drove a Honda Fit with recommended 32 psi tires and 45 psi tires & found very little difference in mpg. I wouldn't tout that as super accurate, because I have problems with how this study was done myself. Wind speed & direction in particular have a huge impact. They didn't keep all the variables consistent enough for me. Even getting a tank of gas somewhere else changes things. As a science teacher, I think Popular Mechanics was lazy in their testing of this. So don't bash me for sharing it. I've already done that!

    https://www.popularmechanics.com/cars/a940/4199963/

    I am finding very little data that shows over inflating tires enhances fuel economy. I am not talking about comparing an under inflated tire verses a fully inflated one here. I am talking about going above the maximum psi rating on the sidewall of the tire. Maybe there's a good reason for that? Who wants to be sued for something that shouldn't be recommended in the first place?

    No one denies under inflated tires reduces fuel economy. I am just being the devil's advocate here. When I research this topic I find - over inflating tires to increase fuel economy is a myth.

    Metro's shared data -

    Raw results for PSI/feet travelled

    20 / 479.3
    25 / 524.8
    30 / 621.0
    35 / 621.0
    40 / 639.6
    45 / 687.5
    50 / 702.0
    55 / 699.3
    60 / 702.0
    Last edited by Mark; 04-14-2020 at 09:44 PM.

  3. #13
    Still Plays With Cars Loren's Avatar
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    Ooooh, I get where you are now.

    "Overinflation" usually refers to being over the CAR manufacturer's spec, which is usually somewhere between about 28 and 36.

    You're correct, most tires (worth having) have a max inflation pressure OF THE TIRE that's somewhere around 44-50.

    Sure, that's not a bad guideline to go by.

    But, 44 psi would be considered by most people to be significantly over-inflated. Mitsubishi said 32, you're running 44. That's the typical logic.

    And, YES, you're going to get better MPG running 44 vs running 32.
    Simplify and add lightness.

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    Quote Originally Posted by Loren View Post
    Ooooh, I get where you are now.

    "Overinflation" usually refers to being over the CAR manufacturer's spec, which is usually somewhere between about 28 and 36.

    You're correct, most tires (worth having) have a max inflation pressure OF THE TIRE that's somewhere around 44-50.

    Sure, that's not a bad guideline to go by.

    But, 44 psi would be considered by most people to be significantly over-inflated. Mitsubishi said 32, you're running 44. That's the typical logic.

    And, YES, you're going to get better MPG running 44 vs running 32.
    Keep in mind - I am questioning Eggman's suggestion of inflating Dunlop Enasave tires to 50 psi. I want to see the data that supports such a suggestion.

  5. #15
    I'm guessing there wouldn't be a noticable difference between 44 and 50psi? And variables like wind might or what you ate for lunch or how much fuel is in the tank might make more of a change? Should call up myth busters?
    Mirage videos:

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        click to view fuel log View my fuel log 2014 Mirage SE wussie cvt edition. 1.2 automatic: 37.7 mpg (US) ... 16.0 km/L ... 6.2 L/100 km ... 45.3 mpg (Imp)


  6. #16
    Moderator Eggman's Avatar
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    Quote Originally Posted by Mark View Post
    Can you show us any data or research that proves over inflating tires beyond their maximum psi rating increases mpg?
    Some people way smarter than me beat me to it. I would have only bumbled the explanation and gotten lost looking or a Wikipedia article as a reference.


    Quote Originally Posted by Mark View Post
    Those numbers don't prove much of a gain. A tire at 40 psi is probably not at the maximum psi rating of the tire. What is gained if the tire is inflated to the maximum rating of 44 psi verses an over inflated tire?

    If we are talking about a tire rated @ 44 maximum psi tire inflated to 44 psi (not over inflated), the gain of going above that would be what? Maybe 1%. From the data share above I wouldn't estimate any more than that.
    Not much. But that Vredestein number that goes to 51 looks pretty sweet, don't you think? Yet another Spinal Tap reference (Whew - got in my requisite Wikipedia link.)


    Quote Originally Posted by Mark View Post
    When it's 90F plus in the summer & Eggman has just traveled a good distance in his Mirage, I would like him to pull out a tire gauge & share the psi of his tires at that moment. I sincerely hope he does that for us some day this summer.
    I doubt I'll get to this. I don't put a lot of miles on Speck, and if last summer is any indication, it will sit in the driveway a lot.

    However (and this is debatable) it is my understanding that an overinflated tire will develop less heat through internal friction than a normally inflated tire. Discuss.


    Quote Originally Posted by Mark View Post
    I am finding very little data that shows over inflating tires enhances fuel economy. I am not talking about comparing an under inflated tire verses a fully inflated one here. I am talking about going above the maximum psi rating on the sidewall of the tire. Maybe there's a good reason for that? Who wants to be sued for something that shouldn't be recommended in the first place?

    No one denies under inflated tires reduces fuel economy. I am just being the devil's advocate here. When I research this topic I find - over inflating tires to increase fuel economy is a myth.
    A-ha! Here we have something nit-pickable. If you mean inflating more then the vehicle manufacturer's recommendation as found on the door jamb placard, then there are fuel economy gains to be had. If you mean inflating more than the tire manufacturer's criteria as found on the tire sidewall, you are spot-on correct - little is to be gained. But of course, all along you focus on the tire manufacturer criteria and not the vehicle manufacturer, so really there's nothing to see here.


    Mark, I hear what you're saying and you make a lot of good points. If you think overinflating tires is not for you, I think that's great.
    Last edited by Eggman; 04-14-2020 at 10:11 PM.

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        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.5 mpg (Imp)


  7. #17
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    Quote Originally Posted by Fummins View Post
    I'm guessing there wouldn't be a noticable difference between 44 and 50psi? And variables like wind might or what you ate for lunch or how much fuel is in the tank might make more of a change? Should call up myth busters?
    No need for Myth Busters. I'm guessing the best benefit is the overinflation would last longer as it leaks down to the sidewall max. Think of it as shooting for the stars...

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        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.5 mpg (Imp)


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    Come on 70 PSI on a 40PSI tire? That sounds dangerous lol. I will give 44 a shot. 50 is not beyond reason. But 70 is almost double the tire manufacturer! As it is every time I take the car in for service they seem to deflate them back to 32.
    Last edited by Mirageman38; 04-14-2020 at 10:15 PM.

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        click to view fuel log View my fuel log 2019 Mirage ES 1.2 automatic: 38.8 mpg (US) ... 16.5 km/L ... 6.1 L/100 km ... 46.5 mpg (Imp)


  9. #19
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    Quote Originally Posted by Mirageman38 View Post
    Come on 70 PSI on a 40PSI tire? That sounds dangerous lol. I will give 44 a shot. 50 is not beyond reason. But 70 is almost double the tire manufacturer! As it is every time I take the car in for service they seem to deflate them back to 32.
    Who said 70 psi? I can't find it.

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        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.5 mpg (Imp)


  10. #20
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    Quote Originally Posted by Mirageman38 View Post
    Come on 70 PSI on a 40PSI tire? That sounds dangerous lol. I will give 44 a shot. 50 is not beyond reason. But 70 is almost double the tire manufacturer! As it is every time I take the car in for service they seem to deflate them back to 32.
    Just sharing information (quoting common sources here) -

    "How hot does the tire get? Typical tires experience a temperature increase of roughly 50 degrees after running on the highway for a half-hour. If it's a 70-degree day, this suggests a tire temperature of about 120 degrees."

    "Just as colder weather can cause PSI to drop, excessive heat can cause your tire pressure to temporarily increase. For every 10 degrees of increased temperature, your tires can be expected to increase by 1-2 pounds of pressure."

    "Remember that tire pressure will increase as the outside air temperature rises. In fact, tire pressure will go up approximately one pound for every 10 degrees Fahrenheit. So, tires that were at 35 PSI back in January when you drove to the slopes could easily be closing in on 45 pounds on a hot July day at the beach. Under some conditions that increase in pressure is enough to blow the tire! If nothing else, a tire that's overinflated will wear prematurely and will cause the car to handle and brake poorly. Don't count on your electronic tire pressure monitoring system to alert you to an overinflated tire, either — the warning light will only get illuminated when a tire’s air pressure is too low, not too high."

    My conclusion - Buy a good tire gauge & check your tire pressure. Even if your tires don't lose much air over time, changes in temperature warrant checking your tire pressure. The TPMS system on a Mirage isn't all that useful.

    Top Fuel has covered this quite well for us - For $50-100 you can add a TPMS system that reports the psi of each tire. If an aftermarket items like this are so cheap, how expensive would it be for Mitsubishi to add something that's actually useful to owners?

    By the way - when one of my Enasave sidewalls blew out, I knew that I had an issue by the sound of the tire while going down the road long before the TPMS light came on. The TPMS light coming on was an after thought long after I had already pulled over. TPMS signals are not constant.

    Just venting - I find TPMS to be more annoying than useful.



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