If you want topspeed, raise the front to maximum height and make suspension and shocks stiffer.
It's the other way around in the back, lower suspension etc.
Also, you should set the downforce settings to the lowest possible.
Then set the gears to the top speed the car is able to go, which you can look up in one thread that I don't want to search for.
Top speed list v2 or something like that.