Is it true that by placing a fist on your windshield you can prevent it from shattering?

Dear Car Talk

Dear Car Talk | May 01, 2003

Dear Tom and Ray:

I am a Peace Corps volunteer in Gabon, in Africa. Maybe you've never been to Africa, but generally, despite romantic images of dirt roads leading off into dark forests, most of the highways in Africa are paved. Except in Gabon. Our national highway is gravel/dirt and is poorly maintained. There are many logging trucks and beer trucks making runs between the capital and the interior, plus Toyota four-wheel-drive minibuses and pickup trucks carrying passengers to different towns. Often when I travel and we pass a large truck going the opposite direction, the driver will put his fist up to the windshield, as if to hold it in place. When I ask about it, they say that this keeps the windshield from shattering if a rock is thrown up by the oncoming vehicle. They say their hand and arm absorb the impact. My question is, have these guys been drinking too much palm wine, or is there real African know-how behind this? -- Hannah

TOM: Well, we think there's a lot of very good folk wisdom out there. Lots of folk remedies have legitimate bases in science. Unfortunately, this ain't one of them, Hannah.

RAY: At least as far as we can tell. There have been international standards for auto glass for at least 30 years. Those standards call for "safety glass" -- glass made like a sandwich, with two layers of 1/8-inch-thick glass on either side of a thin layer of vinyl. That vinyl is there to hold even broken glass together and keep it from shattering and flying all over the driver and passengers.

TOM: Now, I suppose it's possible that if a really large rock were to hit the windshield -- something big enough to tear through the middle layer of vinyl -- then the driver's fist could prevent the object from hitting him. But only if his fist is in exactly the right place on the windshield -- right where the rock or object is coming through. And his hand would hurt like hell!

RAY: The other possibility is that in some poorer countries, people might not use safety glass. Maybe they just replace broken windshields themselves, and do it with cheaper pane glass. But even then, the driver's fist won't prevent the glass from shattering. It'll just prevent the rock from hitting him in the face if it happens to land where his fist is.

TOM: We spoke to Russ Corsi, a glass engineer at PPG Industries, a leading auto-glass manufacturer. He also couldn't think of any way the driver's arm would help. He says that while reinforced glass is stronger than non-reinforced glass, a man's arm, extended from the driver's position, wouldn't do much, if anything, to reinforce the windshield.

RAY: So, see if you can get some more information from these guys, Hannah. Ask them more about what actually happens when the fist is there and when the fist is not there. Get some more details, and then write back to us. We'll be glad to test any of their theories. My brother will do the driving, and I'll throw the rocks.

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