i've had two Vitos and a Viano all of them suffered to some degree with wearing outer edges, the earlier sport and the Viano were notably worse, they had the 17" wheels fitted and hey scrub terribly on tight lock as did my old C Class C230k 202 model and it appears to be the castor angles that cause this, i'm just about to put new tyres on the front of the Viano, tracking is spot on, so as i'm paying for these (not a company van) i'm going to increase the tyre pressures which may take some of the load off the front edges, the set on have only done 14000 miles and they have been swapped front to back once, the rears now have about 3.5mm left as have the fronts but the edges of the fronts (originally on the back) are disappearing quickly, the inside edges are also wearing, but also they are cheap Nexen tyres and i had these on another vehicle and they wore quite quickly and also cracked.