Handling question and my quick fix

I don't know if anyone else noticed this but this is my experience.
When I first got my Gen 2, I noticed that it was quite unstable when driving on highway when I came up close to a large vehicle like a tractor trailer. I guess it's the aerodynamics of the car being very low drag, it is very sensitive to turbulent air around a massive object moving at high rate of speed. Basically the car would bounce around side to side quite a bit. Out of desperation, with some F1 inspiration, I added 4 vortex generator on the rear roof bar figure they wouldn't hurt even if it doesn't do anything. I was totally surprised by the night and day difference they made reducing the bouncing effect to unnoticeable.
A month later Toyota came out of TDR version of Prius aero treatment that included those roof diffusers

Fast forward to this month, I noticed the same bouncing effect on the Prime. I am a little disappointed that they never considered this an issue but perhaps it's the price to pay for low drag. I installed the remaining pieces I had and problem went away.
I know some might think this is total gimmick but it actually made a difference for me. Just want to share my experience in case anyone else is bothered by the same issue.

 

I am sure those sidewalls are weak but that wouldn't really come into play if you are going a straight line on highways.

Those little nubs first showed up on my Subaru STi 15 years ago, under the side mirrors. Supposedly they helped to smooth out the airflow past mirror. Then they showed up in force on the rear roof line of EVO and Gen 2 STI. If you watch racing, you'll notice those and little fins are used extensively to modify airflow around curved surface to delay the flow layer from separating away from the surface . They really don't do anything until higher speeds, and even our highway speed is marginal. We usually drive around 80 MPH on highways (speed limit 65) and there was enough effect to be noticeable. Basically the principle is to keep a bit more air flow following the rear window and hopefully reach the spoiler to provide just a little extra down force to keep the tail stable.

Honestly I initially hoped those to act more like tiny vertical stabilizer as I didn't think the hatch on the Gen 2 had any spoiler effect but I was pleasantly surprised.

This is what it looked like on my old Gen 2.

I'll take a new picture later with them on the Prime.

 

No doubt that nicer tires would help but that's a whole different conversation. Good hear that there's more than one way to solve this issue.

 

Here they are on the Prime. I had 6 left so I put them all on there. I think they actually look better on black background than they did on red.

20191029_151115 (1) by mister2cool posted Oct 29, 2019 at 4:17 PM

20191029_151100 by mister2cool posted Oct 29, 2019 at 4:17 PM

 

Just to be clear. I am not trying to convince anyone that you should do this. I experienced what I felt was troublesome handling issues but it's also because I drive pretty quick in the left lane a lot of times and pass a lot of crazy tractor trailers. I also came from driving mostly RWD & AWD sports cars so the deficiency was clearly obvious. The situation may or may not apply to others, especially if you usually cruise at more modest speeds. Better wheels and tires would help at any speed!
I just wanted to share my experience in case if someone feels the same challenge and it's a cheap fix to test out.

 

I just discovered modification forum.. I guess this thread belongs there. Do we have mods that can move threads into proper place?

 

Wow, I assume this article was directly translated from another language, probably Japanese. It's making me forget how to write completely sentences in English. I honestly had a very hard time understanding the article.

What really caught my attention is the interior photo. The layout doesn't look anything like a Prime with a traditional shifter setup and hand brake. Wasn't Prius C was the only one that had that layout?

Now this would have been an awesome interior for the Prime..

 

Funny that we said the exact same thing about that exact photo!

Yeah but they probably didn't anticipate anyone flying around in these going 80+ passing large trucks who are also going quite fast. As I mentioned earlier, the "bouncing around" really only happens at higher speed in some pretty specific conditions. That's what prompted me to look towards aero factors to find something that might help.
If you take away the lower hatch window, the rear spoiler on Prime\Prius really isn't that much lower than where the wing was on those Sti\Evo, right in the middle of the rear view mirror, and much higher than where you would find a spoiler on most other cars.