Premature wear in the middle can point towards overinflation. I used the recommended 32 psi all round but this caused wear on the edges. I now run 36 psi all round and for the past 30k at each service the measurements across the tire are nice and even.

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2009 135i M Sport Convertible
2008 X5 3.0si
2003 E46 318Ti M Sport Compact - donated to parents
2003 116i Hatchback - donated to brother
2002 316Ti - Sold
2000 318ci M Sport - Sold
1998 318i Sedan - Sold