I'm trying to identify this problem on my wife's car.

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You can't tell from your picture. Feathering will look and feel like the treads of the tire are 'ramped' in one direction. You can feel this by running your hand in one direction (front to back) and then in the other. One way it will run fairly smoothly and the other it will feel like the tread is raised up . It's hard to describe in words, but a local tire guy could show you exactly what feathering means if you took the car to him. Feathering occurs in FWD cars where the tires do not get proper and regular rotation. You will notice this on the front tires only because they are the powered ones. Keep them rotated regularly to avoid this problem.