if your hearing a roar from the tires esp the fronts then its most likely not cupping. cupping is when the tires have uneven wear b/c the tires bounces up and down and doesnt wear similarly. that is the actual definition of cupping. it can be caused by worn shocks and improper balance. what your speaking of is probably the same feathering issue that the Z owners have/had or can be due to alignment.

 

I have been trying to decide whether my new car should be a G35c or a BMW E90. It's a close call.
It was this tire issue (like the Z's have) that finally made my decision to go with the BMW.
Sorry guys.