I drives a lot.

A bunch of stuff has hit the windscreen.

Everything from bugs to sand to rocks has a unique sound, that changes with the impact point on the glass and the speed I’m driving.

Sometimes the whap! of a bug will make me flinch

Some pieces make a cracking sound to a soft thud. Some, I imagine are like a marble would sound.

A rock that looks the size of a baseball coming at me but is really less than an inch across may leave an ugly dirt mark that, when wiped away leaves only a tiny pock-mark.

Then there was Thursday…

Never saw the culprit, just heard a metallic ‘ping’ sound that caught my attention just because it was so unusual.

Later, when the light was just so…a crack sprouting straight up from the very bottom of the windshield.

Reflecting on the experience,

I wonder if the combination of the strike location as well as the density and speed of the rock combined to set up a harmonic that cracked the glass.

I don’t know but I doubt it… I tend to think Newtons 3rd law twas responsible for this one…

Shatto, I Have Seen Technical Service Bulletins For Certain Makes And Models Concerning Windshields Breaking Mainly Due To Improper Manufacturer’s Installation.
This makes me wonder if the windshield was struck at all.

What make, model, and model year vehicle is this one?


Many years ago, when I was a kid of 10 or so, my old man would amuse me (and himself) by allowing me to try to break the front and / or rear windshield of cars he was going to scrap. I’d hit them with a fairly sizeable hammer, only to watch as the hammer bounced off and did no damage.

Turns out the key to breaking automotive window glass is pretty simple: hit it straight on. A glancing blow, even from a hammer, will make a lot of noise but not break the glass. Same is true for whatever else is hitting your windshield.

The edges of a windshield is the critical area…The edges are VERY fragile. New windshields must have perfect edges or they are doomed to a premature death. Impacts that will bounce off the center area and leave just a small pit in the glass will instantly start a crack if near the edge. I believe when windshields are made, the process tends to leave the glass stressed around the edge and any slight imperfection will focus that stress and create a weak point…

Don’t forget that the shape of the object will determine how the force of impact is distributed. If a sharp corner of a rock hits, the area is extremely small and all that energy is concentrated into a small area.

Premature “death”

Most cars in Alaska spends most of their lives with multiple cracks in the windshield.

That layer of plastic and the 2nd layer of glass mean they’re going to hold together pretty well to anything short of a cinderblock hitting them, and if a crack in the windshield is a “distraction” or an “obstruction,” then you’re too easily distracted to be driving at all.

I just don’t think windshield cracks are that big a deal. I mean, sure, get the chip filled before it cracks, even if you’re in a state where the cops/inspectors don’t care. But the idea that a windshield needs replacing because there’s a crack spreading halfway across it is asinine.

(and no, I’m not blaming you.)

I just don’t think windshield cracks are that big a deal

That depends on where you live. In many states…if it’s longer then 4" it WON’T pass inspection.

It’s fairly well known that many of today’s cars rely on the windshield as a structural element. Even the adhesive used to hold it in place is specially formulated for this purpose.

I won’t go into great detail but this is done primarily for two reasons; 1. by using the windshield as a structural element, the size and thickness of the metal around it can be reduced resulting in a significant weight reduction and 2. the windshield is relied upon as part of the air bag restraint system to act as the backside barrier for the bag. Without it, the bag will not hold back the occupant in a crash.

Like most consumer items, there is constant pressure to reduce cost and often a corresponding reduction in over-engineering. I seriously doubt there is enough margin to allow for a 50% reduction in structural integrity of the windshield. Frankly, just because some people can drive around with broken windshields or believe they can withstand a cinderblock being tossed at them does not make for sound judgement when it comes to the actual design limits during periods of critical stress.