The actual weight only matters for accelerating in a straight line. The trick is, the rotors have to accelerate in a circle, too.
Mass at the center of a circle is really easy to turn. That same mass pulled away from the center is tougher to turn. To prove this, sit in your boss's office chair (this is science - he wont mind) and get yourself spinning so fast you feel like yer gonna hurl. Now, stick both your arms straight out -- you'll slow down as the energy that went into spinning fast now isnt enough anymore (your mass moved outward). Pull your arms in again if you dont believe me (your mass moves inward, and that same energy will spin you faster again)
So, by going to a heavier, LARGER rotor, you're hit four or more times.
Once for accelerating in a straight line.
Once for the extra mass to turn.
Twice or more for the increased radius - you're moving the mass outward.
BMW's brakes are great stock. Put on steel braided lines and they kick massive ass. Go to a BBK and gain nothing but mass.
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