I assume you mean Spitfire brand, and no they are great. If you are concerned with weight of products, you probably need to skate for a few years more. and anyway you shouldn't even be thinking about those you should be buying RICTAS!
No
Wheels dont make a skateboard easier to turn on the skateboard trucks do that.
no
yes the sizes of skateboard wheels range from 40-70 mm
Bones wheels
yes
4
Wheels
polyurathayne,
The wheels allow them to move. If you look at a skateboard it has wheels.
Skateboard companies make decks and wheels
There are no trunks on a skateboard, you are probably referring to the "trucks" which are the parts the wheels attatch to.