you must definitely use a racing wheel, you lost 1-2 sec. pro lap with your gamepad.
I use a Logitech Momo Racing Force Wheel, you cant buy it for a low price for the time being.
check this link
ps. let me know what you think about my mod
I play rFactor for 4 years, this definitely the best racing simulator for pc
i have made a mod for this, check it out here http://wtccbmwe90season06-08.blogspot.com/
and here http://www.rfactorcentral.com/detail.cfm?ID=WTCC%20BMW%20E90
ps: check my rfactor screenart page here http://rfactor-screens.blogspot.com/
enjoy