abnormal wear of only one tyre

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I own a tata safari EX. Model: 2009. Date of purchase:13.01.2010. Kms run: 17000.   About 4 months back i noticed the ride abnormal as if the wheel is wobbling on the front left wheel. I found an unusual wear pattern. the middle and extreme points is touching the ground and the space in between has worn out. I had raised a complaint at tata motors. At SRMT, Visakhapatnam after inspection finds everything is normal. the tyre expert also inspected and he too said since the tyre has crossed the warranty period, there is nothing he can do. i would like tata motors to explain the cause for this abnormal wear. it should not happen for the next tyre too.