For moderate to severe over pronators, New Balance has integrated the ROLLBAR technology into the rear of the midsole to maximize rearfoot stability.
A ROLLBAR is a lightweight, flat molded piece of graphite material constructed in the shoes to prevent rear foot movement. When the Rollbar is on the medial side only it provides stability for an extreme pronator (prevents foot from rolling inward); when it is on the medial and lateral side it will provide stability for an extreme pronator and supinator (rolling outwards).
To find out if your shoe has a ROLLBAR, look for the words ROLLBAR written on a gray piece of plastic in the heel area. Or look for a match book size black and blue checkerboard.