Tires: Inner Tire Wear -- Ridge formed (cupping?), alignment problem, rubber compounds

Question
If you can see the pic at this link:
http://img159.imageshack.us/my.php?image=dsc00146xo7.jpg

it will show a dip that has formed.  What causes this?  The car is a 06 GS300 with 18" Dunlop run-flats.  Is it a bad tire or something on the car causing this?  Thanks, Chris

Answer
Chris,

The first thing I notice is that the tires are very nearly worn out.

The second thing I notice is that there appears to be more wear on the inside of the tire, than the outside.  That indicates an alignment problem.  I should also mention that "spirited driving" can also cause this.

But what you are actually seeing is wear at the edge of the belts and the tire has worn enough that you are starting to see rubber compounds other than the tread compound.

So it's time to replace the tires and an alignment is indicated.