[Dave Casey]

Being a second generation Auto Glass shop owner, I will give you my best explanation.

It is strickly a matter of thickness of the glass, thinner is lighter obviously.

Let's look at the windshield first. front windshields are laminated safety glass, which means it is 2 pieces of regular glass with a .030 layer of plastic sandwiched in between. Older cars used 2 thicker pieces, but still the .030 plastic in the middle , todays cars have thinner windshields, they are just as strong, as the strength is in the laminated piece altogether, not the individual pieces. You can save some weight if you find a windshield that is thinner than the one you are taking out. As an example, a factory windshield on a 67 camaro maybe .250 thick, you probably can find one that os .210 thick and save a few lbs. Later cars are harder to find thinner glass for, but often you can still save a little weight because generally the windshields are so much larger that any differance in thickness will help you.

The side and back windows are generally curved tempered glass since the mid 60's. Tempered glass is solid not laminated and basically they take regular glass, form it the correct curve and the temper it in an oven process that basically case hardens it and it can not be altered after tempering or it will break into those little crumbs so to speak. As with the windshield, newer cars have thinner glass. it is harder to find replacement side and back windows that are thinner, and they are seldom if ever thicker, but not as commonly thinner as the replacement windshields are. Basically it is pot luck on finding thinner side and backglass relacements.

When a racer asks me for a lighter windshield I try to get a thickness measurement on what they have and then go to my 4 suppliers and see,,1 who has the glass and 2,, go there and measure the thickness to see if I can help them.

I will guess that the question about a car getting disqualified revolves around an early car that had flat side windows. There are not many of them being raced, but in that instance a glass shop could make a new flat door glass in a thickness of .125 or thicker and then get it tempered(which would make it safe) and install it and save some weight. It would most likely need to be a sedan, not a hardtop because of design issues.

Tom's statement about saving 18 lbs on the whole car with the side and back being reproduced a little thinner is probably the max savings you might see. As Tom stated the glass was made in South Africa, just about all classic reproduction glass is made in some other country, even the "certified gm reproduction stuff" that I have seen.

Bottom line, you can save some weight, but not a ton, and you need to look around for the thin stuff.