Plexi Side and Rear Windows

Very general question here, I know, but no* racing body would require polycarbonate on side or rear windows, right? Just many will require supports on the rear window. Also, even if they do want polycarbonate, is that something that would ever get caught in tech? I'm thinking I can replace the windows in the E21 with some run of the mill plexi. 

The only issue I've had in tech with plastic rear windows is that some scrutineers want the plastic to be riveted in, not screwed so there's no chance of it backing out. 

*The car will continue to see 99.9% vintage racing with the potential SCCA event if I update the cage. 

In for info as Im looking at doing side and rear windows in my 86 coupe in lexan.

Lexan. Its much stronger than run of the mill plexiglass.  Last time I bought 3mm Lexan it was around $9 a square foot at the local glass shop.   3mm, or .125" for sides and rears.  6mm or .250" for front.  Rear needs metal straps.  3/4" wide I think, but might be 1".  Been a while since I did my 02.

I think most bodies requires it to be 1/8" thick polycarbonate. Dont get acrylic since it can shatter.

We had our rear supports mounted to the body then the lexan laid overtop of it then riveted it together. The shop did a great job and it doesnt move at all even at 70+mph.

All of the panels are riveted into place 10" on center.

I had two cars that used plastic windows - TVR rear windows and Jensen CV8 rear side windows. The latter were a pain to replace (they had fogged with age) as the factory seems to have used a thickness that is no longer common.

The TVR was a race car and I was able to install two rods on the inside to hold the roof steady and not allow it to belly out at high speed and they accepted it. I wasn't really fond of the idea of having to drill the rear window and body for bolt through safety clips.

In reply to AxeHealey :

I raced using Lexan until age got to it and it started cracking. Then I replaced it with Plexiglas  and got another 30 years out of it. 

Thanks for the feedback everyone. I think what I used for the windshield was Makrolon and I remember it being quite expensive. That could have been because of the thickness or just my perception at the time. 

Flexibility is something I thought about last night and I think the comment about acrylic is a good one, not just for impact. The rear window isn't very curvy but I don't want to run the risk. 

I think .125" lexan (or the like) seems to be the way forward for the side and rear. 

Thanks. 

Odd about rivets vs screws/nuts. There are some redic fast drag cars with screwed in windows.

In reply to Paul_VR6 (Forum Supporter) :

Many rivets put too great a clamping load on the plastic, causing cracking out of the holes. Probably agravated by drill chatter in the holes as well. The people who do it right use nyloc nuts and make them barely tight.

Paul_VR6 (Forum Supporter) said:

Odd about rivets vs screws/nuts. There are some redic fast drag cars with screwed in windows.

To be fair, I wasn't saying there's necessarily any merit to the concern with screws, just that I've encountered it.

TurnerX19 said:

In reply to Paul_VR6 (Forum Supporter) :

The people who do it right use nyloc nuts and make them barely tight.

...and make the holes slightly larger or elongated because the plastic and metal will expand at different rates.