Originally Posted by Opticon
As long as the tires meet or exceed the stock load, speed, and size requirements you can run different brands on the car safely. But the differences in tread dynamics, wear, temp, and traction ratings will more than likely make for a performance nightmare.
For street tires driven by anyone driving normally on the street, any combination of tires that are in the same ballpark (meaning you're not mixing some 450 treadwear all-season tire with a 140 summer max performance tire) as far as performance will be fine.
Even at 10/10ths autocrossing, I've had success with multiple front/rear mixes (Hoosier A6/Hoosier A6, Kumho V710/Hoosier A6, Hankook Z214/Hoosier A6 so far).