I've always liked playing with the "handling" files in all of the previous GTA's, and still do in GTA IV. However, I never took the time to fully investigate the game's physics and figure out what all of the parameters did (I only played with the ones that made the most sense). Upon searching for a more comprehensive explanation of the parameters in the GTA IV handling.dat, I found only incomplete guesses at what some of them did. Thus, I took it upon myself to do some experimenting (and I do mean experimenting) to make an educated guess at the functions of ALL the parameters, not just a few. I have documented my results in the tables below so that you may use them to your advantage.
I do not claim that these are 100% correct; in fact my theoretical standpoints on some parameters may be far off. But I did my best to formulate likely theories. If anyone sees any problems, or has noticed something different themselves, feel free to point it out and I will look into it, and perhaps we can shed even more light on the game's physics.
Being in the engineering field, I must say I found it extremely annoying that the programmers of this game did not seem to base these vehicle handling characteristics on real life equivalents. When the sum of forces does not equal mass x acceleration, then what can you be sure of?
Nonetheless, the system makes some sense in itself at least, even if it doesn't accurately represent true physics.
I did not play with the flags much, since they are either harder to test or self explanatory. I did include tables of them for convenience.
If you plan on modding your handling.dat (located at "~Program Files\Rockstar Games\Grand Theft Auto IV\common\data\handling.dat"), BACK UP THE ORIGINAL IN CASE YOU WANT TO RESTORE IT!
Furthermore, you need to replace the "filelist.pak" (located at "~Program Files\Rockstar Games\Grand Theft Auto IV\pc\data\filelist.pak") with the modified version found here
. Again, BACK UP THE ORIGINAL BEFORE YOU REPLACE IT!
Now, without further delay, here are the tables as promised! If anyone knows a place where I can host them that will not run out of bandwidth please let me know! The site I used might work but I'm not sure for how long.
I also made a small diagram for coordinate directions in case anyone is unsure.
X Y Z Directions