In the following 2008 Best Motoring video of the M3 vs ISF, the ISF does not have a sunroof and the video states it weighs 3725 pounds (minute 1:10). That is 55 pounds lighter than the listed 3780 pounds for the sunroof version. Removing 50+ pounds from the top center of a vehicle must feel better.

http://www.youtube.com/watch?v=okT7NuBYc64

 

The average person couldn't tell the difference.

 

55 lbs for the moonroof, 35 lbs for the spare, and 30-35 lbs with a low weight battery, that's a total of ~ 120 lbs with relatively low cost.

 

Add 35 lbs from a greddy exhaust, ? 90 lbs + lbs from Bride seats and there's
245+lbs weight savings. Still close to 3600 lbs.

How much would a polycarbonate moonroof replacement weigh? does a glass moonroof really weigh 50 lbs?

 

Im totally in on a carbon fiber sunroof plug group buy.....

 

glass itself probably weighs only 10-15 lbs. the motor, rails and other supporting mechanism weigh the most. a simple replacement of the glas is not going to have noticable benefit.

 

Yeah, but the real world car doesn't weigh 3780. My Supra weighed exactly what the New Car Features said - 3415 - but my IS-F and my IS350 did not.

The only way to know for sure is to remove the sunroof and weigh the whole mess. I doubt anyone is going to do that any time soon.