# Why don't we have windshields that can withstand rock chips? **URL:** \ **Category:** Factual Questions\ **Created:** [April 13, 2007, 2:30am UTC](https://boards.straightdope.com/t/why-dont-we-have-windshields-that-can-withstand-rock-chips/399899 "2007-04-13T02:30:08Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![Chasing\_Dreams](https://avatars.discourse-cdn.com/v4/letter/c/258eb7/32.png) [@Chasing\_Dreams](https://boards.straightdope.com/u/Chasing_Dreams)\ **Post date:** [April 13, 2007, 2:30am UTC](https://boards.straightdope.com/t/why-dont-we-have-windshields-that-can-withstand-rock-chips/399899/1 "2007-04-13T02:30:08Z")
With all the snow melting and all the gravel still on the roads, I am sure that many dopers have been getting rock chips in their windshields. Why don’t we have windshields that can take some rock chips without spreading cracks throughout the windshield? Could we not put a plastic laminate layer over top of the glass to give it protection? Can we not manufacture a pure plastic laminate windshield that doesn’t cause cracks to spread? Surely someone has created a solution to this obvious problem. ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [April 13, 2007, 2:32am UTC](https://boards.straightdope.com/t/why-dont-we-have-windshields-that-can-withstand-rock-chips/399899/2 "2007-04-13T02:32:07Z")
Heck, I’m waiting for a plane made out of the stuff they pack the black box in. ---
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [April 13, 2007, 2:48am UTC](https://boards.straightdope.com/t/why-dont-we-have-windshields-that-can-withstand-rock-chips/399899/3 "2007-04-13T02:48:51Z")
You need a windscreen to be (i) very transparent (ii) hard so it doesnt scratch iii) cheapish (iv) be collision resistant to reduce injuries Only laminated glass comes close. But all glass are prone to cracks. In general, anything very hard is prone to cracking (call it scm1001’s law). One could perhaps design a transparent tough nanocomposite, but it would be extremely expensive ---
**Author:** ![boytyperanma](https://avatars.discourse-cdn.com/v4/letter/b/4491bb/32.png) [@boytyperanma](https://boards.straightdope.com/u/boytyperanma)\ **Post date:** [April 13, 2007, 2:56am UTC](https://boards.straightdope.com/t/why-dont-we-have-windshields-that-can-withstand-rock-chips/399899/4 "2007-04-13T02:56:41Z")
I think the solution is glass insurance that is relatively cheap and companies that are willing to replace your windshield wherever you happen to be. ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [April 13, 2007, 4:31am UTC](https://boards.straightdope.com/t/why-dont-we-have-windshields-that-can-withstand-rock-chips/399899/5 "2007-04-13T04:31:22Z")
Click and Clack dealt with this a couple of weeks ago on Car Talk. They said that in recent years automakers have reduced weight by using thinner windshields and that current ones are about half the thickness of those common years ago. All I know is that four years ago I bought my [first new car](http://www.lfexaminer.com/VIR_0080a.jpg), after having owned used cars for 30 years, and within the first month the windshield had gotten a chip. It has had at least three or four more since then, and I’ve had the windshield replaced already (lots of tiny little scratches), after a little more than 30,000 miles. There’s a chip in the new one right now. Before getting this car, I don’t recall ever having a chipped windshield. ---
**Author:** ![Quiddity\_Glomfuster](https://avatars.discourse-cdn.com/v4/letter/q/c4cdca/32.png) [@Quiddity\_Glomfuster](https://boards.straightdope.com/u/Quiddity_Glomfuster)\ **Post date:** [April 13, 2007, 5:21am UTC](https://boards.straightdope.com/t/why-dont-we-have-windshields-that-can-withstand-rock-chips/399899/6 "2007-04-13T05:21:21Z")
I grew up back east. When the roads were icy, they put sand down. You know, sand - that which may once have been gravel or pebbles but has been worn down to leeetle tiny bits? Then I moved to Calgary. Where the morons put not sand, which does work to provide traction, but stupid pebbles down when the roads are icy. Result - the pebbles get caught in tires or under them, the tires spin them on the ice polishing it nice and smooth, and then the pebbles are pitched off onto others’ windshields. I never saw a chipped or cracked windshield until I moved to Cowgary - where a windshield without a crack was an anomaly. How stupid is it to use friggin’ rocks on the road? You cannot tell me with all the dirt on the planet that they can’t find enough actual sand or sand-like textured stuff to put on roads? I figured that the windshield makers must have a real good lobby in Alberta. Dumbest thing I ever saw, I tell ya. Solution to the issue? Get your local politicians to buy sand - as in the tiny stuff. Tell them if it looks like rocks, then it’s not sand, because apparently some people don’t know the difference. ---
**Author:** ![psychonaut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/psychonaut/32/4655_2.png) [@psychonaut](https://boards.straightdope.com/u/psychonaut)\ **Post date:** [April 13, 2007, 11:16am UTC](https://boards.straightdope.com/t/why-dont-we-have-windshields-that-can-withstand-rock-chips/399899/7 "2007-04-13T11:16:33Z")
[QUOTE=scm1001] You need a windscreen to be (i) very transparent (ii) hard so it doesnt scratch iii) cheapish (iv) be collision resistant to reduce injuries Only laminated glass comes close. But all glass are prone to cracks. In general, anything very hard is prone to cracking (call it scm1001’s law). One could perhaps design a transparent tough nanocomposite, but it would be extremely expensive [/QUOTE] How about making the windshield out of diamond? Ignoring the obvious cost issues, would this be practical? ---
**Author:** ![Will\_Repair](https://avatars.discourse-cdn.com/v4/letter/w/a698b9/32.png) [@Will\_Repair](https://boards.straightdope.com/u/Will_Repair)\ **Post date:** [April 13, 2007, 3:44pm UTC](https://boards.straightdope.com/t/why-dont-we-have-windshields-that-can-withstand-rock-chips/399899/8 "2007-04-13T15:44:36Z")
One [solution](http://www.cleanacar.com/glchrekit.html) is to [repair the chip](http://www.popularmechanics.com/how_to_central/automotive/1272411.html). ---
**Author:** ![Epimetheus](https://avatars.discourse-cdn.com/v4/letter/e/c4cdca/32.png) [@Epimetheus](https://boards.straightdope.com/u/Epimetheus)\ **Post date:** [April 13, 2007, 3:47pm UTC](https://boards.straightdope.com/t/why-dont-we-have-windshields-that-can-withstand-rock-chips/399899/9 "2007-04-13T15:47:15Z")
During the manufacturing process they do put a laminate over the glass to prevent it from shattering. Its not impenetrable, but it reduces the number of cracks. And glass is thinner, but stronger because of the laminates which are pretty new. Any seeming patterns by individuals and their anecdotes is probably misfortune rather than glass being weaker. Unless you had a car in the 50’s when it was made of tempered glass, which is harder, but when it does break it fragments in thousands of pieces, which can be deadly at high speeds. ---
**Author:** ![Jayrot](https://avatars.discourse-cdn.com/v4/letter/j/3ec8ea/32.png) [@Jayrot](https://boards.straightdope.com/u/Jayrot)\ **Post date:** [April 13, 2007, 4:02pm UTC](https://boards.straightdope.com/t/why-dont-we-have-windshields-that-can-withstand-rock-chips/399899/10 "2007-04-13T16:02:38Z")
What about transparent aluminum…oh, wait… ---
**Author:** ![Epimetheus](https://avatars.discourse-cdn.com/v4/letter/e/c4cdca/32.png) [@Epimetheus](https://boards.straightdope.com/u/Epimetheus)\ **Post date:** [April 13, 2007, 4:09pm UTC](https://boards.straightdope.com/t/why-dont-we-have-windshields-that-can-withstand-rock-chips/399899/11 "2007-04-13T16:09:53Z")
[QUOTE=Will Repair] One [solution](http://www.cleanacar.com/glchrekit.html) is to [repair the chip](http://www.popularmechanics.com/how_to_central/automotive/1272411.html). [/QUOTE] Unfortunately it doesn’t always work. Might in a temperature and humidity controlled garage or something, but my several attempts at this (and following the directions to a ‘t’), ended up with no results. Chip still there, wallet missing 14 bucks (each time). ---
**Author:** ![Will\_Repair](https://avatars.discourse-cdn.com/v4/letter/w/a698b9/32.png) [@Will\_Repair](https://boards.straightdope.com/u/Will_Repair)\ **Post date:** [April 13, 2007, 4:32pm UTC](https://boards.straightdope.com/t/why-dont-we-have-windshields-that-can-withstand-rock-chips/399899/12 "2007-04-13T16:32:47Z")
[QUOTE=Epimetheus] Unfortunately it{chip repair} doesn’t always work. [/QUOTE] True but it beats using a replacable polycarbonate shield, or turning the windshield upside down and letting the glass flow over the chip. ---
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [April 13, 2007, 10:18pm UTC](https://boards.straightdope.com/t/why-dont-we-have-windshields-that-can-withstand-rock-chips/399899/13 "2007-04-13T22:18:10Z")
[QUOTE=psychonaut] How about making the windshield out of diamond? Ignoring the obvious cost issues, would this be practical? [/QUOTE] Thats scm1001s law again. It wouldnt scratch as it is so hard, but would shatter very easily as it has no defence against crack propagation. It only takes a very small amount of energy to cleave any object (about 50j /m2 from memory) which is why cracks can (have) split a boat or aeroplane in two (and jewelers only need small hammers to carve diamonds). Any real structural material (bone, wood, concrete) tends to have some composite structure, which stops the cracks at the composite boundaries (metals are slightly different again). A diamond composite might work, but the problem is transparency, as composites tend to scatter light due to the different refractive indexes of the two components. ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [April 13, 2007, 10:27pm UTC](https://boards.straightdope.com/t/why-dont-we-have-windshields-that-can-withstand-rock-chips/399899/14 "2007-04-13T22:27:06Z")
[QUOTE=psychonaut] How about making the windshield out of diamond? Ignoring the obvious cost issues, would this be practical? [/QUOTE] Remember that it also has to meet safety standards. I don’t want to think about what a human face would look like, after going thru a windshield made of something hard enough to cut thru glass!