It's been a long time since I have moded the configuration file but I would suggest first playing with the vehicles top speed as well acceleration, you can at least make certain cars a little faster and have an understanding of how the system works.
Always make sure to keep backup's, and I suggest many as the file is so small and you will be upset.
I would suggest playing with the suspension. if you can make the suspension softer the cars handle better at least for the front end suspension if I recall correctly. You can really mess things up with these settings.
#Suggestion making your cars faster with peak performance as well default handling feel is required as someone might play your server then go to another and feel like the cars are not going anywhere and will return back to yours. I noticed this myself..