That is strange William, the FFB in RBR is very good with the G25.
Hard to know what might be the cause without knowing more about what you have done so far.
Are you only using default RBR? Or are you using RSRBR2010 addon?
If only default, have you installed the patches (1.01 and 1.02).
I assume you have activated the FFB under Options in-game? Did you do the in-game FFB test?
Which operating system are you using? XP, Vista, Win 7?
It may be best to have a chat via TS, let me know a suitable time for you if that would help.
I'll do some more searching to see if others have reported problems.