1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Random Fishtailing of the Rear Wheels of e-AWD at Slow Highway Speed

Discussion in 'Gen 4 Prius Main Forum' started by Cricky, Jan 24, 2022.

  1. Cricky

    Cricky New Member

    Joined:
    Jan 24, 2022
    9
    0
    0
    Location:
    Michigan
    Vehicle:
    2020 Prius
    Model:
    LE AWD-e
    About a month ago, we had our first significant snow and I was anxious to see how my e-AWD performed. I did experience some oversteer going around turns and highway ramps. Then I was going straight on a local highway, about 50 - 55, when the car started to fishtail. I took my foot off the accelerator, steered into the skid and regained control. It was odd but no big deal. The same thing yesterday and I wasn't so lucky -- very sad too.

    I was wondering if anyone has experienced this. I had just bought two Michelin all season radials and put them in the Front. I know the rear wheels are supposed to disengage at 45 but what if there's a fuzzy area where the computer gets confused. Or it could be my shitty tires in the back. But why would a FWD car fishtail going straight?

    I'm just curious.

    Cricky
     
  2. Tideland Prius

    Tideland Prius Moderator of the North
    Staff Member

    Joined:
    Oct 2, 2004
    44,767
    16,016
    41
    Location:
    Canada
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    So there are new tires in the front and old ones in the back? Are they same type?

    The differences in tread depth could cause the unbalance, yes.
     
    Pulse07 and Rmay635703 like this.
  3. Cricky

    Cricky New Member

    Joined:
    Jan 24, 2022
    9
    0
    0
    Location:
    Michigan
    Vehicle:
    2020 Prius
    Model:
    LE AWD-e
    Maybe, I'm not a tire expert. It could be tire pressure also? I was just wondering about other Prius/eAWD owners. I love(d) the car.

    It was really cold and I don't inflate my tires every time I get a pressure warning because it happens every time there's a 5 degree temperature drop at night.

    Cricky
     
  4. Tideland Prius

    Tideland Prius Moderator of the North
    Staff Member

    Joined:
    Oct 2, 2004
    44,767
    16,016
    41
    Location:
    Canada
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    Possibly but it has to be significantly different. I have a Prime with a bigger battery in the back so you’d think the pendulum motion would be more greatly exaggerated in a Prime vs a regular Prius.

    How worn are your rear tires?
     
  5. Cricky

    Cricky New Member

    Joined:
    Jan 24, 2022
    9
    0
    0
    Location:
    Michigan
    Vehicle:
    2020 Prius
    Model:
    LE AWD-e
    Possibly, like 30 percent. Remember that I have more weight in the back also due to the rear AWD.

    Cricky
     
  6. Tideland Prius

    Tideland Prius Moderator of the North
    Staff Member

    Joined:
    Oct 2, 2004
    44,767
    16,016
    41
    Location:
    Canada
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    Not by much. I’d imagine not much more than those with a temporary spare tire. It’s a 7hp induction motor.

    And again, a Prime has much more weight (it’s about 150kg, 350 lbs) more than a FWD Prius.

    Also I just re-read and noticed your speed. The rear motor won’t be active at 50-55mph, so it’s strictly rotational moment of inertia. Either the calibration of the suspension is wrong or I’m blaming your mismatched tire wear for your somewhat unstable handling.

    I guess one way to check is to put 4 new tires on the car and repeat what you did and see if the results are the same or different.
     
    Pulse07 and fuzzy1 like this.
  7. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    17,035
    10,010
    90
    Location:
    Western Washington
    Vehicle:
    Other Hybrid
    Model:
    N/A
    Did you let up on the gas and get a bit of regenerative braking just before the fishtail?

    In theory, if tires are mismatched, the best should be on the rear. Mismatched tire grip, with best in front, is naturally unstable when slowing in poor traction conditions. That is one reason some of us prefer reasonably closely matched tires on all 4.

    Do remember that AWD is not a substitute for good winter tires. All-Season tires are no match for real winter tires, and relatively quickly wear down to just 3-Season tires.
    Either your pressures are too low for this season, or you have the TPMS alert threshold set artificially high. If set normally, it should take around 25% drop to trigger the alert, which is at least 8 psi. By the normal rule of thumb of 1 psi per 10 degrees F, that requires about a 80 degree temperature drop.

    Pump them up higher.
     
  8. Cricky

    Cricky New Member

    Joined:
    Jan 24, 2022
    9
    0
    0
    Location:
    Michigan
    Vehicle:
    2020 Prius
    Model:
    LE AWD-e
    I usually inflate them to 37: 1 PSI higher than the recommended PSI.

    Cricky
     
  9. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    17,035
    10,010
    90
    Location:
    Western Washington
    Vehicle:
    Other Hybrid
    Model:
    N/A
    Did you play some games with the TPMS reset button in order to raise the warning threshold? If so, and a 5 degree drop trips the alert, then you may have set it too close. I've had enough valid TPMS alerts over the years to not want to be misled into dismissing some as false.

    If you didn't play TPMS games, then something is off.
     
  10. sam spade 2

    sam spade 2 Senior Member

    Joined:
    Mar 31, 2018
    7,035
    2,780
    0
    Location:
    USA
    Vehicle:
    2017 Prius c
    Model:
    Four
    This is a BAD habit.
    You don't KNOW why the warning happened unless you check them.
    One might be WAY low due to a leak.
    And if you add a couple of extra pounds in that situation, the alarms should be less frequent.
     
  11. sam spade 2

    sam spade 2 Senior Member

    Joined:
    Mar 31, 2018
    7,035
    2,780
    0
    Location:
    USA
    Vehicle:
    2017 Prius c
    Model:
    Four
    Most all the experts say to put your best tires on the REAR.
    Probably because of the very thing that you are experiencing.

    AND it sounds like you have been driving too fast for conditions.
    The results pretty much prove that.
     
    Rmay635703 likes this.
  12. ColoradoBoo

    ColoradoBoo Senior Member

    Joined:
    Jul 19, 2019
    903
    593
    4
    Location:
    Monument, Colorado USA
    Vehicle:
    2017 Prius
    Model:
    Two
    I haven't noticed any fishtailing in my 21 AWD, even when driving up a very icy hill a few weeks ago, it went pretty straight. I don't think the AWD acts like a 4-wheel drive even in bad conditions...the rear motor only comes on at low speeds and only if the front are spinning.
    And FWIW, the GVWR on my wife's 2017 Prius LE is 3,915 pounds and the GVWR on my 2021 Prius AWD is 4,070 pounds. The AWD has the lighter lithum-ion traction batteries instead of the nickel metal hydride.
     
  13. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    17,035
    10,010
    90
    Location:
    Western Washington
    Vehicle:
    Other Hybrid
    Model:
    N/A
    Am I misremembering? I thought the AWD retained the older NiMH battery.
     
    Pulse07 and Mendel Leisk like this.
  14. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

    Joined:
    May 12, 2018
    6,688
    6,375
    1
    Location:
    Pennsylvania
    Vehicle:
    2018 Prius c
    Model:
    Two
    Definitely want the best tread on the back of the car to prevent spinouts. Yes even FWDs. You may not get going as easily, and you may not stop as short as you'd like, but at least you can keep directional control.

    When our Prius (no AWD) breaks traction it is almost always just one wheel- so the car will skid a bit to one side. That's the trigger. Good traction on your rear tires is what prevents a bit of a turn or skid from developing into a full spinout.

    So I think it is plausible that you are getting into a condition where the front tires are slipping a little, and by the time that happens your rear tires have already lost grip; almost no hope of keeping the back end behind you.

    Swapping front and rear tires should help somewhat.
    Better tires is the real cure.
    Snow tires > AWD every single time.
     
    fuzzy1 likes this.
  15. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    54,470
    38,103
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    New snow tires all ‘round would be my prescription.
     
    fuzzy1 likes this.
  16. privilege

    privilege Active Member

    Joined:
    Mar 17, 2021
    659
    165
    0
    Location:
    Birmingham
    Vehicle:
    2011 Prius
    Model:
    Three

    is the car totaled now ?


    fwd = keep the throttle steady or apply slightly more, if the back is stepping out. rear step out means you have lost traction in the rear, if you let of throttle the front is going to act negatively on the impending spin, and make it worse.

    rwd= heck yes, lift and hopefully the reaction in the front plus very mild smooth inputs will bring the rear in line

    AWD + traction control + abs + electronic stability = who knows, good luck, it's in the algorithms control now

    there were some really aggressive abs systems on bmw moorsicles a while back, when it sensed a lack of traction, it would cut braking force and wait... that's fine on surfaces like pavement where traction and wheel roll are going to happen again.... but it's really really bad in mud, loose downhills, etc ... when reaction didn't happen again and the bike just free wheeled. wet grass was fun too, you never knew how the computer was going to react to the lack of traction. lol

    I think in your case it was just classic "too fast for conditions"
     
  17. ColoradoBoo

    ColoradoBoo Senior Member

    Joined:
    Jul 19, 2019
    903
    593
    4
    Location:
    Monument, Colorado USA
    Vehicle:
    2017 Prius
    Model:
    Two
    I don't know if they all do but it would make sense to keep the weigh down...the stuff for the rear end AWD probably weighs hundreds of pounds.

    I do know the NiMH perform better in cold weather, I wonder if the Priis sold in Canada are mostly NiMH? Toyota probably realizes those of us buying the AWD live in colder areas so it's a win/win for us.

    Don't all the Prius Prime, also, have the NiMH batteries??
     
  18. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

    Joined:
    Oct 28, 2010
    7,668
    6,482
    0
    Location:
    Redneck Riviera (Gulf South)
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
  19. ColoradoBoo

    ColoradoBoo Senior Member

    Joined:
    Jul 19, 2019
    903
    593
    4
    Location:
    Monument, Colorado USA
    Vehicle:
    2017 Prius
    Model:
    Two
    That's true...I've seen plenty of them in the ditches here...mostly on hilly areas because they are going a bit too fast and make the mistake of hitting the brakes while going downhill which is a huge mistake and will make you spin right out of control. One guy, last year, had a brand new Jeep Rubicon and spun out on a road in town and slammed into the sidewalk and his wheel came right off and ended up underneath the Jeep. I don't think they build Jeeps like they used to!!
     
  20. Tideland Prius

    Tideland Prius Moderator of the North
    Staff Member

    Joined:
    Oct 2, 2004
    44,767
    16,016
    41
    Location:
    Canada
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    Prime uses Li-Ion chemistry (different from the regular Gen 4).

    AWD-e models use NiMH.
     
    Mendel Leisk, fuzzy1 and Pulse07 like this.