Only for those who have low fps, this can help you (A bit)
Here's what you can expect in the game after installation:

~Low Quality Cars (vehicles is in normal quality when you are inside the vehicle)
~poor pedestrian quality (square hands, body etc.)
~no lights on vehicles
~rain is less visible
~no clouds

Make ?????? of your original ??????????????.???!

Installation path: Grand Theft Auto IV\GTAIV\common\data