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Selecting New tires 2018 Prius Two

Discussion in 'Gen 4 Prius Fuel Economy' started by KRDucky, Aug 5, 2024 at 3:25 AM.

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  1. KRDucky

    KRDucky Junior Member

    Joined:
    Mar 20, 2023
    26
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    Location:
    US
    Vehicle:
    2018 Prius
    Model:
    Two
    Good morning all, (night shift here)

    So my Prius seems to have a slow leak on all 4 tires since I put them at 36/35 F/R and about a week later they were around 32/30 F/R. Then I filled them to 39/38 F/R and this evening they were around 36/35 but when I got to work they were back at 39/38. Also, the tire temps went from ~84F to 130F over the space of a 40 mi drive in South Texas with the ambient air temp of 84F.

    My fuel economy used to be around 52-53 MPG but over the past month or so I have been seeing ~41-44. I am I lucky I can see 46MPG. Average driving speed is 70. Mostly flat terrain. No hills to speak of. Corpus Christi to Kingsville and back. I am starting to suspect the tires and/or something introducing drag? I don't hear anything out of place when driving but it does "feel" like it takes more oompf to get up to speed and letting off the pedal drops speed a good 5-10 mph really quick but it doesnt slow down to a stop any faster. I used to be able to drop into the green "EV"/"EV assist" mode frequently but now that I am having to basically keep it in gas mode to stay up to speed and with the traffic, the battery bar is full but I rarely drop into batt mode.

    So, I am going through Discount Tire and am looking at tires. I would like some recommendations. Road noise on these Continental ContiproContact tires the dealership installed when I bought the car is making me crank the volume on my sound system. I am considering Yokohama, Pirelli, etc
     
    #1 KRDucky, Aug 5, 2024 at 3:25 AM
  2. OptimalPrime

    OptimalPrime Member

    Joined:
    Sep 17, 2017
    113
    74
    0
    Location:
    Keene/Nashua
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    While I consider 52mpg at 70mph to be normal, I am used to driving on winter tires inflated to 50psi, which actually gives better mpg than stock tires. Having mpg drop 20% without a major change in speed or conditions, is not something I've ever experienced in any Prius, and it's 24 years since I got my first one.

    Personally, I'd check what the "max load at max psi" pressure on the tires might be (hopefully at least 44psi, preferably 50 or 51) and pump up all 4 corners to that value, to see what mpg you get.

    Every Prius has marginal tires specified, where you really, really, really don't want to be driving with any tire at 30psi, that is asking for a blowout due to overloading. Check out the load capacity of tires versus pressure, on tirepressure.org

    I recommend going up several numbers in load index, by buying XL tires. Note that XL tires don't usually reach their full rated capacity until 42psi, unlike standard SL tires which reach theirs at any pressure from 36psi to their max. Personally I go slightly up in size also, from 195/65R15 to 205/65R15 because again it adds load capacity, plus I've never met a Prius that couldn't use more ground clearance. It also got me from load index 89 up to 99, so the tires are expecting the weight of a minivan, and last longer with only the weight of a Prius (which is heavier that you'd think) on them.
     
    #2 OptimalPrime, Aug 5, 2024 at 5:34 AM
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