URBAN LEGEND? or just a bunch of BS?...Windshield topic

FJ Guga · 09-08-2006, 08:58 AM

As I am driving with my buddy. I happened to realize that I have a huge truck in front of me. So I kinda desperately try to go and pass him. Javi, my friend, says "whats your hurry" so I said I have been reading on the forum all the people who's windshield have broken. So he is like "really!!!".

So he starts looking at it and he syas, I bet they are more fragil because the rear view mirror is not on it. And I am llike WHAT ARE YOU TALKING ABOUT???
Apparently when he was younger at his grandpas farm he used to drive an FJ 40 and in ocassions he would see his grandpa stick a couple of fingers to the windshield everytime there was a truck in front of them. His explanation was that, it would help for the pressure.

Sorry if the explanation is confussing my composition skill suck and bein English my second lenguage doesn;t help either.

So what do you think?

I think is bs

sandabbe · 09-08-2006, 09:11 AM

I think your friend really loved his grandpa! I admire that, but, i do believe he is wrong, our honda civic had the mirror on the window and it would crack or chip at just about everything that hit it! I think the windshields are made cheaply now, or they shatter easily for our protection against injuries in the event of an accident and that makes them more prone to fracture!
Test his theory everytime he's with you tell him to keep his hand on the windshield! see for your self!

Kansas Law Dog · 09-08-2006, 09:26 AM

Quote:

FJ Guga previously said:

So he starts looking at it and he syas, I bet they are more fragil because the rear view mirror is not on it. And I am llike WHAT ARE YOU TALKING ABOUT???

Apparently when he was younger at his grandpas farm he used to drive an FJ 40 and in ocassions he would see his grandpa stick a couple of fingers to the windshield everytime there was a truck in front of them. His explanation was that, it would help for the pressure.

So what do you think? I think is bs

The rock impact is very localized on the glass, but because glass is brittle a crack propagates outward from the point of impact due to flex of the glass when the rock hits. A hand on the glass positioned just in the right section could theoretically minimize the flex (due to countering the pressure exerted by the rock) and minize the propgation of cracking.

The reason rock chips can eventually (over time) result in a spreading crack across the glass is due to flex caused by the windshield flex when driving at highway speeds (wind pressure) and/or temperature variations (all materials have a thermal expansion). Although the thermal expansion of glass is small, the steel structure surrounding the windshield has a larger thermal expansion. In cold weather the steel structure shrinks more than the glass, putting greater pressure on the windshield gasket, which is transfers pressure to the windshield. The result is coming out one morning in cold weather and seeing what was a small chip, now showing a growing crack.

The short answer is that "old grandpa" wasn't wrong, but he would have to guess accurately where the rock was going to hit. Some aftermarket company will need to come out with a windshield more resistant to impact.

FJ Guga · 09-08-2006, 09:34 AM

I also forgot to mention that I heard this from couple of other people. Thats why I started the thread.

Sounded kinda interesting

**Woodsman** · 09-08-2006, 09:44 AM

The verticality of the windshield as well as the curvature have the most to do with its strength and ability to withstand the rocks. I'm not sure if or how they might test windshield design and shape prior to production but some vehicles are definitely more suceptible to damage.

My last broken windshield was a mere rock ding until I left my sisters driveway (at slow speed on a freezing day) and the crack grew 20+ inches instantly.

TuxedoFJ · 09-08-2006, 09:56 AM

The Exploder is on its 4th windshield and it is currently cracked from rock impact. It has a nice big mirror attached. Gramps prolly also thoght that "The long way home is the safe way home.." (Heard my Mom-in-law actually say that one.) All the above technical explanations are wunderful but basically ya learned everything you needed to know when you learned to play rock-paper-scissors. (ya I know I kant spell).

FJCameron · 09-08-2006, 10:06 AM

In the old days with our Toyota Land Cruiser or FJ40 (my families first vehicle when I was a kid) my dad would use some plexi-glas and a metal frame holder to protect the windshield. We grew up in Northern BC where logging trucks were a dime a dozen.

RubiconSS · 09-08-2006, 10:09 AM

Our windshields are nice and Big and Flat and straight up. ONLY difference between my FJ windshield and my Jeep is - Size. I've had three(3) windshields in my Rubicon (it's an '05) NEVER hear any comments or complaints on the Jeep Forum.

It is what it is.

REDLINE · 09-08-2006, 10:19 AM

I wonder if the H3 guys have any problems....aren't they're windshield shape, dimensions, angle similar to the FJ's?

**Woodsman** · 09-08-2006, 11:18 AM

Quote:

RubiconSS previously said:

Our windshields are nice and Big and Flat and straight up. ONLY difference between my FJ windshield and my Jeep is - Size. I've had three(3) windshields in my Rubicon (it's an '05) NEVER hear any comments or complaints on the Jeep Forum.

It is what it is.

RubiconSS, out of curiosity, what does a Jeep windshield cost ?

The FJ windshields wouldn't be such a big deal if they were competitive with other windshields. For example, a new windshield on my business truck ('04 Chevy Silverado) was less than $175 installed.