To my understanding the only things that matter in your car are:
Power
Torque
Weight
Downforce
Front tyres in the beginning of the race (believe it or not, the rears do nothing, neither does changing to a softer compound in the pits)
Getting a racing suspension doesn't change a thing, neither does getting racing brakes or an entirely new drivetrain. There's a thread on this somewhere, I'll have a look and see if I can find it.