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

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.

 

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.

 

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.

 

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.

 

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.

 

Am I misremembering? I thought the AWD retained the older NiMH battery.

 

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.

 

New snow tires all ‘round would be my prescription.

 

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"

 

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??

 

FWD cars don't.

https://www.kellyjeep.com/posts/blog-awd-vs-fwd-vs-4wd-whats-the-difference#:~:text=AWD%2C%20which%20stands%20for%20all,only%20when%20it%20is%20required.

Sometimes it's the 4WD and AWD cars that wind up in the ditches during ice and snow because they are the most likely to be the ones who get out over their skis.

 

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!!