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Moving Forward
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I'm not sure if this was ever talked about and I know some people know about the ins and outs of Tire/Rims. Just to help the ill-informed you must always realize when you put on a new rim and new tire sizes you change the amount of weight that each tire produces when you stop. I don't think jumping up just 1 inch on a rim will do much, but i also see people getting wider tires. Even though a Rim may be lighter then stock compressed air isn't. The more volume of air the heavier it become, which mean that it create more weight when you stop. With this in mind don't forget your braking system. I have seen in a few places where people have been discussing poor brake performance. If you increase the weight load during breaking you will also increase the distance it takes to break. It is possible, but unlikely, that you could cause your brakes to fail. Like i said, i don't see much chance with a small increase in size, but the bigger and fatter the tires and rims the heavier they can become. If you want a good idea of equalization to the Stock parts just weigh the tires and rims and then do the same with the Aftermarket ones. If you want an even more technical look at breaks take a look at this article http://www.4wheeloffroad.com/techarticles/3286/
 

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Ummm yeah, without getting too detailed; I agree that the overall difference in unsprung weight is a factor in stopping distance but the weight of compressed air would be such a minimum difference that it's not worth mentioning. Lighter unsprung weight helps not only ease load on a braking systems but also eases the stress on susepnsion and driveline components (i.e. final drives) as well.
 

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All Show and a l'il go!
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I agree that the overall difference in unsprung weight is a factor in stopping distance but the weight of compressed air would be such a minimum difference that it's not worth mentioning. Lighter unsprung weight helps not only ease load on a braking systems but also eases the stress on susepnsion and driveline components (i.e. final drives) as well.
+1!
 

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Hendo Goat
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That article isn't applicable to the wheel/tire changes that would be made on a GTO anyway. The article is biased towards 4x4s going to huge offroad tires that are of course going to weigh more and have more internal volume for air than the stockers did. On a performance car most aftermarket wheels are going to be lighter than stock and since we aren't increasing the overall tire diameter(we couldn't even if we wanted to with our wheel wells), alot of the time the internal volume of the tire is going to basically be the same or less depending on what size wheel you go up to.
 

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Don't Taze me Bro
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638 Posts
Fill it with helium, that should offset the weight of air.
Especially when it all leaks out after a couple days/weeks. Those tiny helium molecules won't last very long. Try Nitrogen instead.

The air mass will essentially make no difference.

It's the rotating inertia of wheel metal & tire rubber at a larger diameter, a.k.a. Mass Moment of Inertia, (even if same weight as orignal or slightly less) that adds the effective additional weight for braking and acceleration. And the longer radius (if going to taller tires with larger rolling circumference) increases the mechanical advantage over the brakes & drivetrain producing less braking and accelerating force put to ground. Essentially if you go to a taller tire, you will loose rwhp/rwtq and braking force.

But overall, the lighter unsprung mass the better.
 

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Beer Geek
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Just for future reference, 13 cubic feet of standard "air" weighs one pound. If you are doing math in your head on a decompression stop worried about drowning, 15cf = 1 pound.

At 35psig, or about 3ATA, ~~about~~ 4 cubic feet of increased tire capacity will hold enough air to raise your unsprung weight ~~ABOUT~~ one pound.

Buying cheap cast rims on the other hand...
 
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