回复：摸一下轮胎边, 看是否象齿轮. 多谢老大指教。前轮的确是有齿轮状磨损的痕迹。

Below is what I found in eHow, any further specific idea to my case? (So grateful to your help!)

What are the Causes of Scalloped Tire Wear?

Bad Components

• Oftentimes scalloped tire wear comes from a number of factors working together. The greatest culprit, though, is a weak suspension system. Compromised suspension components could include bad struts and loose ball joints, wheel bearings, shock absorbers, springs or bushings -- really any part that helps connect the wheel to the car. Additional factors include underinflated or out-of-balance tires or improper wheel alignment. When these factors combine and become serious enough, you'll likely get scalloped tires.

Bad Tires

• Poorly made tires are susceptible to this condition. Even tire manufacturers who have good reputations make lower quality tires that are more prone to abnormal wear, such as scalloping. So while loose suspension components set the stage for scalloping, cheap tires expedite the process. Unfortunately, the tires that come standard on new vehicles tend to be in the cheaper category, so consider upgrading to better tires to prevent tire scalloping.