CUPPING:
Cupping, which is more accurately described as scalloping (see pictures, but we will use the more common term "cupping" here), 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 (thank you for that Mr. Tire!). 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. Upon examination of the pictures at left of our sample rear Avon, our dusted front VTX Dunlop D256, and the picture of our chalked Dunlop D206 one can see how the cupping follows the tread pattern. 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. As one can see, the simple tread pattern of the Avon pictured produces a simpler scallop pattern while the more complex VTX D256 Dunlop is somewhat involved, though still easily seen in our photo. Cupping on the Valkyrie Dunlop D206 is very hard to photograph because of the complex tread pattern. 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.
The following textual illustration comes from Martin who contributed to this article by E-mail on June 26, 2006:
I was just reading your bit on "cupping" and thought I'd share with you how I describe what's going on. I usually tell people that 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.) I next tell people they can demonstrate to themselves what's happening by taking 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. Then I tell them to 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 seems to make the concept easier for many to understand. Cheers!
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Originally Posted by djltoronto
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