Dusterbd13-michael MegaDork
11/30/21 9:38 a.m.

Looking at dropping weight in the challenge car. The car is a hatchback and has a lot of glass.

Im leaving the windshield glass for scratch resistance, assuming I don't break it getting it out. If i do, lexan is the only option there.

But the rear glass: lexan or acrylic? Acrylic is far cheaper and more available here, but....

Also, scratch resistance: i was thinking clear paint protection wrap on the outside and cheap window tint on the inside should make it way more durable, and still cheaper than lexan. 

As far as mounting: pop rivits and silicone caulk right? Or if i can save the rubber gaskets can I reuse them?

Is there anything im not thinking about here

Ed Higginbotham
Ed Higginbotham UberDork
11/30/21 9:47 a.m.

Commenting to follow. Been wondering the same thing to replace the rear door glass on my E36.

nocones UberDork
11/30/21 9:52 a.m.

I used "Lexan" from Home Depot for the LMP360 windshield.  It's fine.  I had to clamp it on because the 360 uses a gaskets and I didn't own the gasket.  With the gasket the metal flange was to narrow for rivets so I just put down weatherstripping and used a carpet transition extrusion to rivet to the body and clamp the windshield.

Stampie MegaDork
11/30/21 9:59 a.m.

In reply to Dusterbd13-michael :

IIRC window tint doesn't stick to lexan well.


Edit found the answer

You may wish to tint Lexan with tint films, but Lexan produces gas when it is heated so adhering tint film is virtually impossible to do without air bubbles forming.


¯\_(ツ)_/¯ PowerDork
11/30/21 10:02 a.m.

Maybe I'm missing something but I didn't think there were a whole lot of rules concerning windows at the challenge.  Maybe run it with no windows there and buy the good stuff after?

kevinatfms HalfDork
11/30/21 10:05 a.m.

Alot of series require Polycarbonate(Lexan is the big manufacturer) and do not allow acrylic due to its tendancy to fracture and break into projectile like pieces.

We went with 1/8" thick polycarbonate in our Elantra with rivets on the side windows and rear window per Champ Car rules.

Also, rear window in some series require 2 strips of metal to hold down the window in case of a pressure differential which will blow the window out.

For a challenge car it might not be a problem to use acrylic but if you ever wanted to enter the car into something else you will need to replace it with polycarbonate. Just food for thought.

Floating Doc (Forum Supporter)
Floating Doc (Forum Supporter) PowerDork
11/30/21 10:28 a.m.

In reply to kevinatfms :

You make a good case for using polycarbonate, so does anyone have any suggestions for the cheapest way to get buy it? 

The Morris came with a cut down golf cart windshield. I don't know what the material is, assuming polycarbonate. 

Tom1200 UltraDork
11/30/21 10:29 a.m.

If you're going to keep the car more then 15 minutes use Polycarbonate/Lexan.  I've always found acrylic to be far less durable, I've used both in a commercial setting.

What kind of price difference are we talking about?

Captdownshift (Forum Supporter)
Captdownshift (Forum Supporter) MegaDork
11/30/21 11:07 a.m.

Laminex will work better than tint is regards to adhesion and protection for scratching. 

GameboyRMH MegaDork
11/30/21 11:17 a.m.

Yeah acrylic is generally not allowed for safety reasons, it is quite weak and brittle and still scratches fairly easily, although not as easily as Lexan. Compared to acrylic, polycarbonate is softer and more flexible but much harder to break. Think glass vs. hard rubber. Definitely get some kind of coating on it if you don't want it to accrue scratches because somebody looked at it wrong.

Keeping the glass windshield is a good idea, changing the windshield from glass to Lexan is a much bigger pain than the other glass due to wind loads and possible wiper action. For mounting the lexan, you'll actually want to use bolts or rivets with oversized holes in the Lexan to allow for thermal expansion. Fuzzy velcro strips are often used for sealing lexan to the body on cheap race cars, obviously this doesn't actually seal very well, but the large thermal expansion of lexan makes that difficult. You may want to use gravity to keep the rain out, with small gutters/visors above the lexan for example.

Keith Tanner
Keith Tanner MegaDork
11/30/21 11:23 a.m.

Look in the yellow pages* for "plastics". You can probably pick it up locally for a good price without having to resort to a big box store. 

I've had a polycarbonate rear window on the Targa Miata for nearly 15 years. Rivets and silicone, no special treatment. It still looks good and has shown no signs of ill effects from our high temps and strong sun in the summer at the track or the work parking lot, although it does live inside.

*or do the google thing, but I'll bet the book will actually work better

David S. Wallens
David S. Wallens Editorial Director
11/30/21 12:03 p.m.
GameboyRMH MegaDork
11/30/21 12:40 p.m.

^I see that one was glued/rubber-mounted in like a stock glass windshield, have there not been any thermal expansion issues?

preach (dudeist priest)
preach (dudeist priest) Dork
11/30/21 3:15 p.m.

We had to use poly for our LeMons car due to the rules. Purchased last year when EVERYONE wanted clear plastic separating them from other humans, I paid out my ass for enough to do a '92 GTI.

My teammates finished the install and I have not seen it since. The plan was rubber isolated and panhead screws. I did install a "T" of aluminum in the middle of the windshield for more structure.

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