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Higher PSI for better MPG? Maybe not?

Discussion in 'Ford/Lincoln Hybrids and EVs' started by acdii, Dec 13, 2012.

  1. acdii

    acdii Active Member

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    Here is something interesting I ran across today. Before my trip from IL to FL, I raised the PSI from 38 to 45 in my Goodyear Eagle LS-2 tires on my Fusion Hybrid. Well the resulting MPG was far from stellar, horrid even, far below expected.

    This morning before taking it to the local dealer, who failed miserably in getting a tech to test drive the car and confirm the drag, I reduced the tire pressures to 36 PSI. My MPG improved.

    Looks like the Goodyear tires, dont do very well overinflated. Car still has drag, still is far under EPA, but city driving i saw an improvement up to 50 MPG on an 8 mile trip.

    Tomorrow I head home, and reduced tire pressures down to factory of 34 PSI and will see how it goes.
    Will be interesting to see if reducing the tire pressure helped, would be just the opposite as I have done on my previous 3 Hybrids.
     
    #1 acdii, Dec 13, 2012
  2. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    there are other forces at play here. increased tire pressures to a point will reduce rolling resistance and increase your mpg's assuming no other changes.

    at this time of year there are a million things that can affect mileage. wind speed, cold, precipitation, etc.
     
    #2 DaveinOlyWA, Dec 13, 2012
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  3. xs650

    xs650 Senior Member

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    Correlation ≠ Causation
     
    #3 xs650, Dec 13, 2012
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  4. DavidA

    DavidA Prius owner since July 2009

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    I always see MPG go down on longer road trips, where the average highway speeds are in the high 60's and low 70's or beyond. Past 70mph, I see 5 MPG drops, or more, immediately.

    The difference in wind drag between highway and local speeds probably far outweigh the difference in tire pressures.
     
    #4 DavidA, Dec 13, 2012
  5. cwerdna

    cwerdna Senior Member

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    #5 cwerdna, Dec 14, 2012
  6. Codyroo

    Codyroo Senior Member

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    This is one of my wife's main mantras
     
    #6 Codyroo, Dec 14, 2012
  7. xs650

    xs650 Senior Member

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    #7 xs650, Dec 14, 2012
  8. F8L

    F8L Protecting Habitat & AG Lands

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    You must perform a more scientifically sound test before making any conclusive statements about the effect if tire pressure on fuel economy. I suggest designing an ABA test.

    In clinical work
    Copied from EcoModder.com

    Keep reading: How to properly test modifications (AKA: don't believe every MPG claim you read) - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com
     
    #8 F8L, Dec 14, 2012
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  9. Paradox

    Paradox Prius Enthusiast / Moderator
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    #9 Paradox, Dec 14, 2012
  10. SageBrush

    SageBrush Senior Member

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    Yep!

    For a bit of history and smart thinking, Koch's postulates were used in the early days of determining if a bacteria caused disease is a gem:

    1. Find the bacteria in a sick person
    2. Inject the bacteria into a healthy volunteer, and see if disease develops
    2a. Find the bacteria in the volunteer.
    3. Inject serum from the (previously) sick person into another healthy person and see if disease develops.


    This is really an expanded version of ABA, designed to differentiate association from causation. Nowadays though, we just refer to XKCD:

    [​IMG]
     
    #10 SageBrush, Dec 14, 2012
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  11. Codyroo

    Codyroo Senior Member

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    Acdii,

    It will be interesting to see if you do see continued improvement at lower PSI. I realize it seems that we are piling on, but it is just that your observations/results/conclusions seems to contradict what many others have experience or measured. Thus, assumptions need to be inspected and clarified and the conclusion will need to be supported by more data.

    For example, we assume that your commute is on a relatively smooth surfaced road. If you mentioned that there is a ton of pot holes in your drive and your tires are constantly bouncing around, then you'd get some converts who understand that such condtions would be detrimental to MPG's for someone with full inflated tires.
     
    #11 Codyroo, Dec 14, 2012
  12. acdii

    acdii Active Member

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    Well, my return trip I gained ~3 MPG. I had reduced the tire pressures to 34 PSI, which is what the manufacturers recommended on the car. I had taken a 10 mile trip in ~40 MPH traffic and saw 50 MPG for the first time on this car.

    Since these are not LRR known tires, it could be that the Goodyears are affected by higher pressures in such a way that they gain resistance instead of reducing. Maybe the tread pattern scuffs more? I dont know, but I was Extremely surprised when the car acted more Hybrid like with 34 PSI vs 45 PSI.

    However, the car does not get anywhere NEAR EPA! I tried from 55 to 65 and the results were the same, ~38 MPG, with cruise, without cruise, its pretty consistent at 38 MPG. Increased it to 70 and 75 and got around 35 MPG.

    It's going to the Dealer next week and have Ford deal with it. I never had this much trouble getting decent mileage out of my 2010 FFH. I could EASILY get 38 using cruise at 70 in the 2010, and exceed it by quite a bit at slower speeds. Heck I got 50 MPG on a 65 mile highway trip with temps in the 60's, and where I was with temps in the 70's could barely crack 40.
     
    #12 acdii, Dec 15, 2012
  13. Trollbait

    Trollbait It's a D&D thing

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    Maybe the higher pressure magnified another issue like the alignment.
     
    #13 Trollbait, Dec 16, 2012
  14. F8L

    F8L Protecting Habitat & AG Lands

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    Your tires are LRR if they are the factory tires. Nearly all cars in this segment are equipped with LRR tires as designed to the car manufacturer specifications. Manufacturers equip cars with LRR tires in an effort to meet CAFE standards.

    You also state that you drove one direction then changed tire pressure and drove back. Unless you drove on the same exact stretch of road, in the same direction, in the same weather, and at the same speed there is no way to know if the air pressure change had any effect. You could have been driving downhill on the first trip and uphill on the return trip or into a slight headwind. See where this is going?
     
    #14 F8L, Dec 16, 2012
  15. acdii

    acdii Active Member

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    2400+ miles up and down mountains, from Rockford IL to Florida to Rockford IL, dry weather, and rain, Cold temps and warm, Seems like the MPG went up a couple when I reduced pressure, see where I went on this? I took the same roads going down and coming up, and the temps were pretty consistent throughout the trip. I saw no significant difference when I went from cold to warm, and the only real change I saw was going from the rain to dry, which is expected, and was roughly 2 MPG. I used the Ecocruise, and kept the speeds at 70 or below, mostly below, between 60 and 65 for the most part.

    F8L; As far as the tires, Take a look at what comes standard vs the premium 18" tires.

    Michelin Energy Saver A/S

    Goodyear Eagle LS-2

    If you look at the Michelin, it clearly states it is a LRR tire, and I agree with you on that, but the second tire, which is what came on my car, goes totally against what you said, it is not a LRR tire, otherwise it would be noted.

    I am almost positive the tire is what is causing my grief with this car, and nothing else.
     
    #15 acdii, Dec 16, 2012
  16. F8L

    F8L Protecting Habitat & AG Lands

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    The tire does not have to be noted for LRR by TireRack. There is often a difference between tires that comes as OEM and the same model tire that is sold aftermarket. The car manufacturer decides the design for OEM and the tire manufacturer can make changes to the aftermarket tire. This is often the case but not always. The fact you have an 18" tire would lead me to suspect it is likely not very efficient even if it is considered LRR by Ford.

    I'll submit the Toyo Proxes A20, OE 17" tire for Prius, as an example of a very LRR tire that is not labeled as LRR on TireRack.com.

    Toyo Proxes A20
     
    #16 F8L, Dec 17, 2012
  17. F8L

    F8L Protecting Habitat & AG Lands

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    I wouldn't argue the tire is hurting you. The Energy Saver A/S is the most fuel efficient tire we know of in North America. The LS2 not so much.
     
    #17 F8L, Dec 17, 2012
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  18. acdii

    acdii Active Member

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    Have to agree there, those who have the Michelins, are seeing very good numbers on the same car, those with the goodyears, not so good. I have the Michelins on my 2010 and I get EPA all day long in that.

    Going to see if Ford will do something regarding the tires so I dont come down on them like a brick banshee. I did it with the F150( maybe thats why they are ignoring me), and they stepped up on that one.
     
    #18 acdii, Dec 17, 2012
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