Ok, i did not want this to become an argument so i guess i ll have to start with somethign.
I thought i ll start with downforce since that is kind of the only thing i really understand.
When we look at some basic physics we know that the
frictional force = coefficient of friction * the normal force exerted
Now the normal force is the force the ground pushes on the object, in our case our car, which has exactly the same value as does the force that our car pushes on the ground (Newtons law)
If we increase the downforce on our car, we increase the normal force yet the coefficient of friction is the same since we always use the same tires, well pretending we do. Since the formula above is gonna give us a bigger frictional force that means that our car can turn better in corners since it has more friction. The bad thing about downforce though is that by increasing it, we decrease acceleration, because the air pushes on our car alot more now, so with we decrease max speed too, AND we increase tire wear. Since the tires have alot more friction with the road due to the increased donwforce, they will wear alot faster. This should not be a factor to consider at all when u are racing agains ur buddy for the fastes lap in time trial.
Well that is basically all i know about the downforce, the thing i am not very clear on is what increasing/decreasin the front/rear does to your car, besides what they already say in the game when u try and set up the car.
I hope this is a good start to something big, and please please please help with ur knowledge.
PS: for those who feel offended or whatever for me makin the cindy crawford comment, I apologize, yet i couldnt help it. Sorry. heheh