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Minimum thickness for lexan (polycarbonate)?


ELEPHANT1

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Ok I did a quick search (after searching the rules) and I don't see much on a minimum required thickness for front lexan/polycarbonate windscreens. Or any for that matter. Is there one? I would have figured it would be in the CCR but perhaps that's something that is regulated by an individual series. Anyone?

 

Reason I ask is that I was looking at various thicknesses for my front screen but realized that BMW CCA (and possibly others) will require 6mm min thickness for '10. 6mm is friggin' thick....and not all that light. So my thoughts are whether or not NASA has a min...if so is it or will it be the same? If not, do I now simply run glass since there is little, if any, weight benefit? Or do I move further away from CCA CR and run thinner polycarb for the weight advantage?

 

The questions in the second paragraph are rhetorical though obviously feel free to respond to those if you desire. ; )

 

Cheers.

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This is one of those weird things where I have some idea what it should be but can find no rule on what it must be. Anyone point a blind man to the fountain of knowledge? Danke.

 

Cheers.

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It's not in the CCR, I've looked plenty. I've seen cars running 1/8" (just this last weekend), and even with a couple of supports in the middle, I could see it flexing going down the straight.

I was originally going to go with 1/8", but went with 3/16" instead, mainly because the 1/8" was actually .118", and the 3/16" is .177" (Percy's Speedglass). The 1/8" is really flexible.

If you go with 6mm (1/4"), you will probably only need one support bar in the center.

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Originally I was planning on 3/16", I agree that personally I think the 1/8" is too thin. But now I have to consider whether or not I plan to run in BMW CCA at all which will require 6mm for '10. I suspect other series may adopt the same, maybe not. If I opted to use the 6mm I'd just stick the stock glass back in, I doubt there would be any measureable weight difference. I've never had a problem with glass as some others seem to, I wanted lexan for the weight savings.

 

Thanks for the replies! Cheers.

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Even with 6mm (1/4") Lexan, you'll probably save 25-50% of the weight of glass.

Lexan is 50% lighter than glass at the same thickness. What is the glass thickness? 4-5mm?

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Yeah, perhaps so. I though I had my stock windscreen right here to measure but can't seem to find it. Hmmmmmm....perhaps I'll do lexan afterall. ; ) The thing that sucks about the 6mm stuff is that I don't know that it will "bend" well if I were to buy a flat sheet....that was my plan. Anyone have experience "forming" 6mm stuff?

 

Cheers.

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Out here in SoCal the Porsches use .25 thickness. One thing about lexan, great when new and well taken care of. After a while tho the pits and scratches, make it very difficult to see when the sun is beeming at you going into a corner. We usually end up going back to glass for that reason. Seems like everything wants to stick to it. Plexiglass windshields are not allowed, simply because a good rock will break it.

 

Sergio....SoCal GTS

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Anyone have experience "forming" 6mm stuff?

 

Cheers.

 

Just for reference, SCCA specs 6mm front and 3mm rear. I recently cut and formed my own Lexan front and rear with those sizes. The 6mm bends just fine, no issues whatsoever. If you wanted added scratch protection, get Lexan MR10 but it is about 2x the cost of regular polycarbonate. There is a definite weight savings, even with 6mm, I did not weigh but could feel the difference when handling stock glass vs. poly.

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Alright, maybe I'm making this out to be more than it is. I'll find my stock glass and weigh it, then go from there.

 

Cheers.

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Out here in SoCal the Porsches use .25 thickness. One thing about lexan, great when new and well taken care of. After a while tho the pits and scratches, make it very difficult to see when the sun is beeming at you going into a corner. We usually end up going back to glass for that reason. Seems like everything wants to stick to it. Plexiglass windshields are not allowed, simply because a good rock will break it.

 

Sergio....SoCal GTS

 

 

Untreated polycarbonate scratches REALLY easily and can get pretty hazy quickly. I put in some poly rear quarter windows and had a local clear bra guy apply the 3M film he uses and it turned out great. I can wipe the windows without worring about scratches and it doesn't optically distort anything.

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Polycarbonate scratching is the reason I'm going with Percy's Speedglass. You can rub steel wool on it without leaving a mark. Truly amazing stuff. You can also get it with an anti-fog coating on the inside.

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I just put in a front lexan windshield from SHEILDS (stock trim, 1/4" thick) and it weighed in at 16-17 pounds max (not completely accurate as it was hard to measure it on the scale I had).

 

I would have gone thinner but, BMW Club wants 6mm now.

 

 

 

Mike

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Yeah, I gots to find the stock glass so I can weigh it. According to the ETK the stock screen weighs 10.1Kg. Sometimes it's accurate, sometimes not so until I weigh what I have here I won't know for sure. Vaguely remembering moving that piece around I'd believe it weighs 20lbs, not sure if more though. Anyway, gotta find it.

 

Cheers.

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My qualification to respond: I sell a ton of Lexan windshields...

 

Thoughts: The difference in weight on most average cars between each step up in thickness is about 1 lb. (ie a 3/16 windhsheild will weigh 1lb more than the same size in a 1/8". Err on the side of safety!

 

3/16 is the MIN for a windsheild hands down. Why? Unless you have horrible cataracts the flexing and visual distortion at higher speeds will drive you bannanas. For street guys I recommend 1/4" because they never put supports in. racecar guys, 1/4" without supports, 3/16" with...

 

Rear windows? 1/8" is fine...

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