A detailed tutorial would be awesome but I wouldn't pass up on hints and tips since I know nothing about gear ratios.
Mapu's post didn't describe where this tool came from or what it does, so I went looking to get some understanding. This is where one can learn more about this tool:1. Took me a bit to find it again, but here's a really convenient setup development tool. I used it a lot when I was new to creating race car setups:
http://robhermans.org/downloads/R2P_Setup_Tool_Installer.zip