Increase rFactor framerate:
By editing your rFactor desktop shortcut and including these two commands "+fullproc" and "+highprio", you should see an increase in the framerate, it will vary depending on your system and what mod you're running. To do this you right click on your rFactor shortcut:
<== Add "+fullproc +highprio"
This shouldn't have a negative effect, I happened to gain about 20FPS but I've heard some people claim it gained them about 100 fps. Good luck and tell me if this helped!