If you go and look in this thread at
reply #5 by
RP#62 you will see the two situations side by side.
http://www.valkyrieforum.com/bbs/index.php/topic,38548.0.htmlWhat you can't see is the backside of the rotors, where there is a difference.
On the old style rotors the mounting surface is relieved, while on the new style rotors the mounting surface is a positive offset. These both being in relationship to the braking surface of the rotor.
This explains why you can install an old style rotor on a new style wheel using shims to place the rotor in the proper position relative to the caliper.
And this also explains why you cannot put a new style rotor on a old style wheel since that will place the rotor too far outboard in relation to the caliper.
***