Tyre wear - outer edge nearside front. Why ?

The outer edge of my front near side tyre seems to be wearing at a faster rate than the rest of the tyre. Just wondered if this is a symptom of enthusiastic roundabout use, or could indicate a tracking issue. Car is an E39 M5, tyre a Goodyear Eagle F1. Bit grieving to have to buy more, given the rest of the tyre is ok ? Any thoughts...