you gotta go in the folder where you have it installed theres a folder called data open that and theres a file called handling.cfg open that with notepad.[if word wrap is on uncheck it [up top under format] makes it alot easier.] you'll see that all the cars have a bunch of numbers after the name divided up by letters uo top of the file tells you what each does. basically what i tweak is j and k this is for traction. bump j up to about 1.2 or 1.3. [your preference. depends on if you like the drift or tight-ass cornering.] n and o this is for top speed and acceleration i take n up to 999 and o to 99. if you want no damage go to the end to y and set that to zero.
the first one "b" is for mass i think this is what you want for makin the cars fly. i never really tweaked this much so i dont know if it will effect the suspension or not but you can raise that number a fair amount and try it and if alls well go back raise it some till it starts messing up.
that should basically hook you up you can do some wild things with the suspension too but i usually have to do the tweake and try method. i got my dirtbikes jacked up so the seat is just over tommys head. looks funnier than hell. but you cant really do wheelies anymore tho.