Depends on which wheel you have more than anything....different models require different settings in rF. The older Logitech MOMO's require you to run negative settings in some mods, some require postive settings.
My first suggestion would be to get the RealFeel or LeoFFB plugin(s) for rF. The latest version of RealFeel incorporates some of Leo's settings into it, too
RealFeel v0,92 You'll have to make a rFactorCentral account to download it. If you don't want to do that, PM someone here and I'm sure they wouldn't mind sending you the latest version of it.
Edit - There's actually a RealFeel 0.936 out....a new .dll. I can't remember where I got it from, but I don't think it's available at the link I gave you. I'll see if I can find a link for it or you can PM me and I'll get it to you.