Supination, the opposite motion of overpronation, occurs when your feet and ankles bow out instead of tilting in. So if the outsides of your shoes wear out faster than the insides, this could be your problem.
SOLUTION SHOE: The New Balance 1080V2 can help, creating a smooth transition as you move from heel to toe. The rubber outsole is flexible and light, without compromising the protection that your feet and ankles need, while the dual-density foam provides you with the best of both worlds — a soft support against the foot for a buffer and a firmer density foam for support. ($135, newbalance.com)