Coupla points in a discussion where I think enthusiasm running high, physics running out.
1.). Going to a lighter "rotor" means lousier brake all things equal (which they may not be; you got ceramics, you can have more capable and lighter, no problem). The P+ brakes are better in part because they are bigger and heavier and can handle more heat than the base version. Now if the rotor includes the "hat" and you get lighter by virtue of a lighter hat, then you may not be making much of a backward step on the performance of the brake. It should be noted that by cutting the weight out of the hat instead of the rotor itself, you would get the same improvement in unsprung weight as with a reduction in rotor weight, but not as much effect on rotational inertia because of it being closer to the center of rotation. Just as much help, then with suspension performance, but not as much with acceleration/deceleration.
2.) Though weight reduction likely to help slightly in efficiency, certainly not as dramatic as can be conceivably gained by reduction in wind resistance or rolling friction. Much of that is because you cannot recapture with regenerative braking that which is put into frictional losses. You can gain back what is put into acceleration/speed by means of efficient deceleration. That is a major reason behind the electric vehicles doing so well in city driving--low speeds, low frictional losses, good recapture. As a result, I am skeptical about significant gains being claimed for lighter wheels, brake, tires. They are all easier to accelerate (THAT is why race cars use those approaches and why ceramic brakes were developed--they can get REAL HOT and still work well and can therefore be made much lighter than steel), but they also give back less when comes time for regen and they have virtually no effect on friction-related losses. The sources quoted provide some absolutely ludicrous claims based on bogus physics and marketing baloney.
