Ok, the reason I suggested staying with 4 tires all around and not mismatching is because of at-the-limit vehicle dynamics. Let's say you have Brand A on the front wheels and they happen to be very sticky in wet conditions, wheareas Brand B in the rear does very poorly in wet weather. Under normal driving circumstances everything is fine. However when you near the limit of adhesion in either an aggressive avoidance maneuver, or perhaps take an off-ramp a little too fast, it can create spooky handling. Having the rear end of the car swing out suddenly (yes it's unlikely I agree) can be hard for many people to catch. Most modern cars understeer at the limit and thus the nose just pushes when you overcook it, but if you get some glue like tires up front and some rock-like tires on the rear things change. I used to race autocross years ago and a change of a few pounds of pressure would be enough to upset the handling of a car, nevermind when you mix brands. So that was my logic. Didn't want you to think I was just pulling things out of the air here.