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New Tires- Big Mileage Drop

Discussion in 'Prime Fuel Economy & EV Range' started by BirbLuver, May 12, 2024.

  1. BirbLuver

    BirbLuver New Member

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    I replaced the OEM Ecopia EP422 tires on my 2017 prime back in December. I choose Continental True Contact Tour which are marketed as low rolling resistance ["EcoPlus Technology"].

    I saw an immediate and dramatic drop in mileage on my daily commute (100 miles roundtrip on the highway, same route every day). Initially the drop was about 20%. After 5 months/7000 miles, I am seeing something closer to 15% higher gas consumption than the OEM tires for the same weather conditions.

    I thought that part of the issue was change in tire diameter (revs per mile) but I checked the odometer reading for my commute and it is actually reading higher (higher revs per mile) with the new tires. Odd given that the old tires were practically bald. Based on this, the mileage loss probably a bit worse (by a few percent) than I thought initially.

    Has anyone else seen such a dramatic drop in mileage with new tires ? Anyone have experience changing out the OEM tires for Continental True Contact Tour ? If so did you see a big drop in MPG ?

    Anyone know of a source for accurate rolling resistance test data on new tires ? I thought I was buying low rolling resistance tires but apparently you can market anything as LRR regardless of the actual performance. Would like to avoid this problem in the future but how ?
     
  2. bisco

    bisco cookie crumbler

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    percentages can be misleading, what were your former mpg's and what are they now?

    what tyres pressure are you running?

    who installed them, could any of the brakes be dragging?
     
  3. BirbLuver

    BirbLuver New Member

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    My MPG varies quite a bit with temperature. The initial 20% drop (back in December) was from ~62MPG to ~50MPG. Right now (mid May) I am seeing about 56 MPG. I would have expected about 66 MPG this time of year with the old tires.

    I run about 2psi over the factory recommended pressure.

    The work was done at Walmart and they did use the wrong wheel nut torque (off by a different amount on every nut) and underinflated one tire. I did not see any obvious problems beyond this.

    My initial thought was that there must be a problem with the brakes. In an attempt to rule this out I did all new rotors & pads and cleaned/greased everything. I don't think the brakes are dragging, although I guess there could be something weird going on that was not obvious with the car jacked up and the wheel off.
     
  4. Kenny94945

    Kenny94945 Active Member

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    FWIW, short answer tire pressure - increase by 4 pounds and report back.

    The long answer is the rolling resistance rating difference of the OEM (or former) tire vs. the Conts.
    Even if both say 400, the rating is as compared to same-brand tires, not between competitor brands.
    Ditto, the tire pressure door sticker is for OEM tires and may be different settings for aftermarket/ other brands.
    A pyrometer is a great tool to own (as is an accurate tire pressure gauge).

    Lastly, brake drag is a valid comment as mentioned above.
    Lubing the brake pad pins is good maintenance plus a failing/ old 12volt battery is also known to reduce mileage.
    Both items have been discussed on our forum before.

    Good luck.
     
  5. bat4255

    bat4255 2017 Prius v #2 and 2008 Gen II #2

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    New tire tread is typically less stable (squirrly) than worn tires due to the tread depth. It does take some time for them to "scrubb-in"

    When I changed my tires I saw a 2-3 mpg drop even after 2-3 PSI increase from normal (33 to 36 psi).

    After 5,000 miles I did get 1-2 mpg back.

    I also noticed you changed out in December. Did it get colder temps after the tire change?

    Cold weather really eats mpgs. Typically I get 35 in winter and 45 in the summer heat. (40 mpg avg.).
     
  6. Danno5060

    Danno5060 Member

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    It's probably too late, but were there any signs of unusual wear on the old tires?

    Jack up the front end and try to wiggle the wheels side to side to check the tie rod wear and bearings. Wiggle up and down to check the ball joints and bearings.

    Maybe try the same on the rears to see if there are any bearing problems there too.

    Maybe check the alignment?
     
  7. Mendel Leisk

    Mendel Leisk Luddite

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    Replacing the the stock Michelin Pilot HX MXM4 (in 215/45R17, on our 2010), with Michelin Primacy MXM4, our mpg dropped, near 10% IIRC. That was a few years back, and it’s only partially recovered to date. Is what it is.
     
  8. BirbLuver

    BirbLuver New Member

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    Not sure if folks saw my response to Bisco. My response was held up for moderator review. Just in case, I have copied it below.

    kenny9494, I replaced the 12V battery (no improvement). "the rolling resistance rating difference" do tire manufacture's publish a rolling resistance rating ? This is news to me. I did not run into this when I was shopping for tires.

    danno5060, I have not see any evidence of alignment or suspension problems. The tires I replaced had 80,000 miles on them and tire wear was remarkably even.

    Mendel, what you describe seems similar to what I am seeing except I think I am seeing a slightly larger drop.

    bisco:

    My MPG varies quite a bit with temperature. The initial 20% drop (back in December) was from ~62MPG to ~50MPG. Right now (mid May) I am seeing about 56 MPG. I would have expected about 66 MPG this time of year with the old tires.

    I run about 2psi over the factory recommended pressure.

    The work was done at walmart and they did use the wrong wheel nut torque (off by a different amount on every nut) and underinflated one tire. I did not see any obvious problems beyond this.

    My initial thought was that there must be a problem with the brakes. In an attempt to rule this out I did all new rotors & pads and cleaned/greased everything. I don't think the brakes are dragging, although I guess there could be something weird going on that was not obvious with the car jacked up and the wheel off.
     
    Danno5060 likes this.
  9. Mendel Leisk

    Mendel Leisk Luddite

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    See rear brake drag link in my signature (on a phone turn it landscape to see signatures). It’s Gen 3 but Gen 4 rear brakes may be similar. The rear brakes can be reassembled with misaligned brake caliper piston, and this imposes drag on wheel rotation. May or may not be a factor, but good to check.
     
  10. pasta4breakfast

    pasta4breakfast Junior Member

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    How many miles did the OEM tires have on them when you replaced them? If these were the factory installed tires in 2017 and you are driving 7000 miles in five months, I would assume the old tires had a lot of miles on them. I would think really worn tires would get phenomenal fuel economy. when I switched from the OEM Dunlop East save tires with 43,000 miles on them to new Michelin X tour tires, I noticed a 10% drop in EV efficiency. It took over 20,000 miles on the x tour tires to notice any improvement. It took almost 40,000 miles to gain half of the loss back. I don’t know what the loss would have been if I had something like 70,000 miles on the OEM tires.

    Also, because the MPG includes the EV range, small changes in efficiency can wildly swing the number. For example, take a 90 mile commute with 30 miles EV range and 60 miles per gallon when driving in HV mode. If the drop in efficiency of new tires changes your EV range to 25 miles and your mpg in HV mode to 50 miles per gallon, your total MPG drops from 90 MPG down to 69 MPG. In this example a 16.7% drop in efficiency lead to 23.3% drop in the mpg displayed on the dash. I think the miles per kWh gives a less distorted picture. There is a display where it shows you the monthly miles/kwh. I recommend looking at that. I included a picture on my dash as a reference.
     

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  11. BirbLuver

    BirbLuver New Member

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    Mendel, I read you posts regarding parking brake & rear brake drag before I did the rear pads/rotors. Pretty sure that I got it right when assembling.

    pasta4breakfast, I am not charging so the MPG is not affected by EV operation.

    I think I got unlucky with my choice of tires. Going to have to consider replacing them early. Wish there was some way to determine rolling resistance prior to purchase.
     
    Mendel Leisk likes this.