yeah as i said, its complicated. I think its a bit misleading Slip angles are important but to say that they are the cause of oversteer/ understeer (ie to define based on them)is like saying okay so weight never gets transferred around the 4 tyres and wheels never change their camber. ie the "grip" (ability of the tyre to create lateral force) is only dependant on slip angles, which isn't true. I guess its used because its an easy definition a one size fits all cop out, i am not saying its not correct, but i think it is ambigious.

For example imagine a car is steered instaneously away from straight ahead, ie the front slip angle is the steer angle and the rear slip angle is zero because you haven't started to turn. so that means this is understeer? no it doesn't.