Nev, wonderful edit and explanation. I can see why my original Ferrai was lacking depth and didn't have the smooth look I was after. That vertical bit (the air intake for the engine) was bothering me, because I couldn't quite get the height I was after. And now the tyres pop out instead of looking like flat rectangles
Sponsorship I guess is one of the key components on an F1 car, and is true that it forces me to use more colours. Of course Text and symbols at this size become negligible so it's the general shape I should be trying for - rather than trying to downscale and accurately depict logos.
Massive thanks Neverest, I'll update the other cars with my the tips I've picked up from your post.
EDIT: For those interested, there's a few reference images here:
Ferrari 248 F1 Chassis Top View.
DOUBLE EDIT: Updated version of the four cars. Removed the dithering on some of the cars and replaced with solid shades. Also increased the number of grey shades as Nev suggested. Added highlights to the wheel axis of all cars, and cleaned up the third car a bit. Also replaced all the tyres with Nev's as well as adding the tyre manufacturer to the side of the tyres (they lean inwards slightly on F1 cars).
Still a few things to fix I think - but I can't see what it is! Jaggies are still an issue I think.