Why do Windows go up and down?
 

Specifically why are the windows designed to dip down when you open the door and then go up when you close the door?

It has to do with it being a frame less door and to provide a better seal.

And so they don't disintegrate when you close the door a bit to hard.

It's for the rubber seal. I can't cite any specific design materials, but I've been pondering it myself and come up with this: The window contacts the rubber when you close the door, then the window rolls up which pulls, almost even rolls, the rubber tighter to the glass. This should make it harder for air to get past because it has to "unroll" a little bit instead of just being pushed away from the glass by an air stream along the seal.

One of the complaints about early frameless designs were rattling windows, and this would also be helped by having a constant cushion of rubber tight against it.

Having owned a couple of older cars with frameless windows I say whoever came up with this system should get a medal!
As I said above one of the biggest issues was that every single time you closed the door the glass would bounce off the rubber seal. Not only did this risk damage to the glass it also slowly wore the seal right out. They would eventually cut a line right through it. Even before reaching that state the wind would whistle through to gap that was being created.
These nice and gently slide up over the seal so it isn't getting beat to crap every time you close the door.

It used to really irritate me when, getting in and out of my old Celica coupes and Fiat 124, friends would slam the doors closed by the glass. Those old cars had incredibly balanced doors and easy latches. No reason to slam them and absolutely no reason to use the glass to do it.

Even a gentle push would bounce the glass off the seal. I would love to see the rebound in slow motion!

Hmm. So I need to fix it eh?

I would yes.

Part of it has to do with the air pressure inside the car.

Ever notice how some car doors are easier to close when the windows are down? That's because if the door seals are good, the door wants to bounce off the cushion of high pressure air inside the car when the windows are up. The door pushes in a lot more air than you realize*, and even though the cabin isn't airtight, the air can't escape other parts of the car fast enough to reduce the pressure.

With a framed window that's just a nuisance if you're wimpy. But with a frameless window that backpressure against the glass can damage it. It can wear out the mounts inside the door from excess flexing or jarring. It can damage the seals along the bottom of the window from flexing, letting water inside the door. And it can damage the body seal just from the glass bouncing against it as it farts out the air pressure.

So the indexing feature lowers the glass enough to relieve the pressure when the door closes, then slides up to provide a seal. Everything lasts longer as a result.

*BTW, you can use the amount of air pushed by a door to your advantage. If you come out to a really hot car in the summer, roll down the passenger side windows, then open and close the driver's side door several times with the window up. The door will pump the superheated air right out and reduce the amount of cooling time your A/C will need to make the car comfortable.

I'm not sure if this still works in your year, but in the earlier years there was built-in protection to disable indexing to prevent damage if the window stuck to the seal. Sometimes it will get confused or tripped unintentionally and turn itself off. There's a procedure here to turn it back on using the window buttons:

https://www.ft86club.com/forums/show...24&postcount=3

It is the window's nature to act so, on the constantly moving wheel of Dow Jones & Inc.

^^very solid advice. Auto down/up window activation with door openings has been a feature on frameless door cars for the last 15+ years, this isn't something new. However, it is one more reason that I do not like frameless doors.

Also, what does this question have to do with the 2nd Gen BRZ?

Well, in a pure sense, Gen2 appears to have frameless windows.

Probably about 75% of the questions asked here are in the wrong section. I gave up trying to combat that a long long time ago.