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Old 11-15-2012, 12:02 PM   #1 (permalink)
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I was recently reading some of the revisions made to the new Impreza model. One of several weight reducing revisions was reduction of glass weight. Iíd assume that the way to do that would be by using thinner glass. Iím wondering if Subaru was able to increase the impact resistance of the thinner glass or, will owners see an increase in broken windshields?
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Old 11-15-2012, 12:05 PM   #2 (permalink)
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I hadn't heard that.

I've read that , for some vehicles, up to 40% of the cabin's structural integrity is in the glass.

wonder if going to framed windows was part of the reason for less glass?
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Old 11-15-2012, 02:05 PM   #3 (permalink)
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In order to maintain low curb weights and reduce them wherever possible, Subaru uses technologies in its vehicle bodies and mechanical features that allow lower weight with increased strength. Greater proportions of high tensile strength steel are employed in all Subaru bodies, and strong, lightweight metals are used in components throughout the model lineup.

In addition, lightweight unit-body structures are the foundation for Impreza, Legacy, Outback, and Forester models. These same models have window glass of reduced thickness.

Measures taken under the hood reduce weight, too. All Subaru engines have aluminum-alloy blocks and cylinder heads and all Subaru transmissions have aluminum-alloy cases. Not only does this construction reduce overall weight, it helps to improve the front/rear balance of the vehicle for improved handling. The enginesí pistons have a lightweight design, and the intake manifolds are made of resin, which also contributes to weight reduction.

The 2012 Impreza pushes the envelope farther with optimized lightweight aluminum-alloy wheels and aluminum-alloy rear brake calipers.
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Old 11-15-2012, 02:11 PM   #4 (permalink)
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The "structural" connection is correct, but only for the glass that's fastened (glued) to the car body, not the windows in the doors and that can be lowered and raised.

The weight of a particular glass, such as a windshield, isn't necessarily an indicator of the its strength. A lighter glass can be "stronger" than a heavier piece -- it's all in the way it's made.

Every once in a while there's a thread here, and in other forums, about broken windshields and, inevitably, the posts turn to the frequency this is being experienced compared to previous cars. I believe one of the major reasons for this is not the way the glass is made, but the way it's mounted. Earlier windshields were installed to the body using a grooved rubber ring around the body opening. The glass was not glued to the metal, but instead "floated" in the rubber. As a result, body twisting etc did not affect the glass as it was isolated from the changes.

But now that the glass is fastened (glued) into position directly on the body, it becomes part of the structure, but also is subject to the stresses of body twists and changes. The rubber-like glue that's used should normally provide for this, but it has it's limitations. Changes in the body around the windshield will cause tension and stress to build up in the glass. Glass itself is somewhat flexible, but in severe cases, the window might all of a sudden crack with no apparent reason. In other instances, it will not, but hit the stressed windshield with a stone at high speed, and that tiny bulls-eye can quickly become a crack along the stress line(s) in the glass. This, I believe, is what leads to the thought that newer windshields, and other car glass, isn't as strong as "in the old days". But I don't think that's really the case.
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Old 11-15-2012, 03:04 PM   #5 (permalink)
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Quote:
Originally Posted by plain OM View Post
The "structural" connection is correct, but only for the glass that's fastened (glued) to the car body, not the windows in the doors and that can be lowered and raised.

The weight of a particular glass, such as a windshield, isn't necessarily an indicator of the its strength. A lighter glass can be "stronger" than a heavier piece -- it's all in the way it's made.

Every once in a while there's a thread here, and in other forums, about broken windshields and, inevitably, the posts turn to the frequency this is being experienced compared to previous cars. I believe one of the major reasons for this is not the way the glass is made, but the way it's mounted. Earlier windshields were installed to the body using a grooved rubber ring around the body opening. The glass was not glued to the metal, but instead "floated" in the rubber. As a result, body twisting etc did not affect the glass as it was isolated from the changes.

But now that the glass is fastened (glued) into position directly on the body, it becomes part of the structure, but also is subject to the stresses of body twists and changes. The rubber-like glue that's used should normally provide for this, but it has it's limitations. Changes in the body around the windshield will cause tension and stress to build up in the glass. Glass itself is somewhat flexible, but in severe cases, the window might all of a sudden crack with no apparent reason. In other instances, it will not, but hit the stressed windshield with a stone at high speed, and that tiny bulls-eye can quickly become a crack along the stress line(s) in the glass. This, I believe, is what leads to the thought that newer windshields, and other car glass, isn't as strong as "in the old days". But I don't think that's really the case.
No doubt go look up the glass research and development done for the glass used on smart phones and tablet PC's amazing stuff! I'll take engineered lighter glass over old school heavier thicker glass anyday.
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Old 11-16-2012, 11:12 AM   #6 (permalink)
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Subaru has been lightening their glass for years. I remember reading about it on my 2005 Impreza.

I will add that I have had to replace a windshield on both of my previous Subarus ('05 Impreza, '08 LGT) twice on the impreza. I insisted it was because of the lighter glass, yada yada yada.

Then I started driving my wifes Hyundai daily.. I chipped the windshield within 4 months and it spread to a crack because the glass company couldn't schedule a repair soon enough. She drove it for 5 years before me with never a chip. Luckily the glass is MUCH cheaper in the Hyundai than it was in my Subarus.

I've now come to believe it may be the driver more than the glass

I tend to follow closer and drive at higher speeds than my wife...
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Old 11-16-2012, 02:22 PM   #7 (permalink)
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It would appear to me that the angle of deflection of the impact object would factor in the incident.
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