You gotta work the wheels and axles to do anything. BTW,
www.scoutstuff.org now has colored wheels.
Now back to the weight, you can go stupid on all the physics and engineering that goes into where the weight goes posted on the internet. I seem to put mine right in front of the rear axle and up a bit. It has to do with the profile of the track I've been running on.
Have fun and good luck.