Inconsistent Fuel Economy

Discussion in 'Gen 3 Prius Fuel Economy' started by PriusHog, Aug 23, 2013.

  1. PriusHog

    PriusHog New Member

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    2012 Prius Two, 60k miles.

    I drive the same route everyday to work. It's 125 miles round trip and almost all flat highway driving and I cruise 60 mph to and from. My work commute covers at least 90% of my total driving miles. From the time I bought the car until 40k miles, I got about 56 mpg on every tank as I would reset the trip-A every time I filled up. At 40k miles my MPG went up to about 61 MPG and maybe even 62 MPG. I attributed this to the "break-in" of the car. The last three tanks have been down to about 53 MPG with no change in the car. My tires had not been replaced since purchase and I bought the Yokohama Avid Ascend which is actually a step up from what came on the vehicle. Still the gas mileage is low after new tires. Both sets have/had nitrogen. I know there are many factors that effect MPG but just curious if anyone has had the same experience. Thanks
     
  2. xpcman

    xpcman Senior Member

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    New tires need to be "broken in". Also, old worn tires give the best MPG. Sum up these two factors and you can get a 4 to 7 mpg difference.
     
  3. bisco

    bisco cookie crumbler

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    but you're saying your mpg's dropped with the old tyres and didn't improve with the new ones?
    i have no idea why you mileage went up, don't think it 'broke in' at 40k, so i would be thinking more like you dropped from 56 to 53, which isn't much, and could be caused by something as small as air conditioning.
     
  4. nh7o

    nh7o Off grid since 1980

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    You might get better advice in the GenIII forum, this is for GenII and there are some differences. But winter vs. summer gas makes for MPG change. What is the tire pressure? Set them to ~40 psi. (Nitrogen is of no consequence.) Cold vs. hot weather is a noticeable effect, with heater or A/C etc. You are doing fine in any case.
     
  5. Britprius

    Britprius Senior Member

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    New tyres will normally lower mpg.
    New tyres will need to bed in (cure) before they begin to get better mpg. New tyres are also larger in diameter than the worn tyres removed from the vehicle.
    Say you have 1/2 an inch of tread on a new tyre, this will increase the diameter by 1 inch or the circumference by 3.142 inches.
    Now a typical Prius tyre rotates about 850 times per mile. 850 x 3.142 divided by 12 to give answer in feet = 222 ft. This is 222 ft per mile extra distance that your odo does not record, this is 2.1 miles extra in 50 miles not recorded since your odo only records wheel revolutions 850 to the mile.
    Your car actually travels further but does not record it.

    John (Britprius)
     
  6. PriusHog

    PriusHog New Member

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    Thanks for the replies. And yes, the MPG dropped before I installed the new tires and did not get better afterwards. I live in Arkansas and I was getting fantastic MPG for the past 20k miles during hot and cold temps and then the sudden drop. The tire pressure is fine as I check at least once a week and I just had the 60k mile service this week as well. I will continue to monitor and hopefully it will get back to where it was. By the way, I have never reset the 'trip-B' on my car and it reads 55.6 MPG. I love this car!
     
  7. Marcius

    Marcius New Member

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    How's the mpg now?
     
  8. bisco

    bisco cookie crumbler

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    not bad for a 2012, you?
     
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