In any case by setting this variable to =60 for example, you can remove micro-stuttering, however in places where your framerate is below 60FPS the game physics will slow down, and in places where your FPS rises above the iFPSClamp value, the game physics will speed up. The skipping seems to occur because certain frames are dropped to keep up with the physics tic rate. By default it's set so that they're synchronized (=0), however this is known to cause 'micro-stuttering', or more aptly, frame skipping - see the Troubleshooting Tips section for a discussion of this and some solutions.
IFPSClamp=0 - This variable appears to control the synchronization between game physics and graphics, or something similar of that nature. BUT better solution is to open file 'srFalloutStutterRemover.ini' and there is lines. This have 2 choices: - Search your fallout main folder 'stutter' if you remove it all fps increased and not cause damage to game. Well i don't recommend to use the iFPSClamp tweak, this is what it does. I got main menu FPS 190 and game with 200+ mods my fps increased 30 to 80. Best explanation so far of how iFPSClamp works!!