the bias between front and rear is for differing weather conditions.You want to have more bias on the front in the dry and there is more braking force on the front due to extra grip and the car therefore pitches more,unloading the rear more. You need to take braking power off the rear in those conditions cause its alot easier to nip the rear wheels the more thay are unloaded. So in the wet you want to drive the bias towards the rearas grip is less available on the front therefore less dive and the rear is better grounded.