It's not just the mass reduction that matters, it's the fact that this is the part of the car furthest away from the suspension. Therefore, you save perhaps a tiny bit of weight, but the car's rotational inertia around two of the three axes is reduced more dramatically (i.e., it helps mostly in the corners, but also a little bit during accel and braking). This is a much more beneficial weight savings than if they, say, reduced the seats by the same amount.

 

I'm sure the lighter roof makes enough of a difference. There must have been a reason why Mitsubishi went through all the trouble to develop this. This will most certainly lower the center of gravity.

After lifting the steel hood on my eclipse and then lifting the aluminum hood on my EVO, I realize how much weight difference there is between the two. The roof covers a little more surface area than the hood, so a 25-30 lb weight difference sounds about right.

 

Just to put it in perspective aluminum weighs 33% +/- 1% of what steel weighs at the same thickness. So if the roof on an 03 weighs 30 lbs. the roof on the MR/RS would weigh 10 lbs. mol

 

That's only assuming you use the same volume of material. I'm pretty sure to get the same sort of stiffness with aluminum they had to use a little more than they had to with steel - but yes, you do save some weight, but not 20 lbs.

 

Ah didn't think of that. I was just assuming that the materials would be the same thickness, but your right to get the same rigity (spelling) you would have to make it thicker. That means less weight reduction.

 

When I was working on Forumla SAE in college, teams who chose to use aluminum to build their chassis had to use larger diameter tubing to achieve the same strength.

Since the aluminum is being used as a structural member in this case, I would imagine the volume material would be slightly different compared to the steel unit. This is probably why the aluminum roof is shaped slightly differently.