found interesting read here, http://www.rattlebars.com/tirewear/
summarized if you don't want to use the link
Cupping, which is more accurately described as scalloping is a natural wear pattern on motorcycle tires and it will always follow the tread pattern. It is not a sign that you have bad suspension parts. It merely shows that your tire is indeed gripping the road when you make turns.
This cupping develops within the side wear bands of a leaned motorcycle. The extreme forces that come in to play when the bike is leaned in a turn are what produce the effect and when the wear becomes sufficient, one will experience vibration and noise when one banks into a turn.
The leading edge of the tread does not flex much as it grips the road and the rubber is scuffed off the tire in that area causing a depression. As the tire rotates, the pressure moves to the trailing edge of the tread pattern where the tread flexes more causing less scuffing so less material is ground off the tire.
The more complex the tread pattern, the more complex the cupping pattern will be. The softer the compound of the tire, the sooner this cupping will develop. Radial tires are more prone to cupping than are bias ply because the compound of radials is softer.
Low tire pressure will exacerbate this wear pattern and you will lose many serviceable miles by running low. Improper balance has nothing to do with cupping on a motorcycle tire. Improper balance will merely cause your bike to vibrate within certain specific speed ranges.
what's happening is that the individual "blocks" or "islands" of tread are squirming and deforming due to the forces applied to them during cornering and braking. When this deforming takes place, the wear is naturally not evenly distributed across the surface of the tread. (I define a tread block as an area of the tire surface surrounded by a groove.)
As a visual representation take a new pencil with an unused eraser on the end and while holding the pencil perfectly vertical, push down and drag the eraser on a rough surface in one direction. Look at the eraser and note that all the wear is on the leading edge and not evenly distributed across the end surface of the eraser. It makes the concept easier to understand.