The inside 2" of tread on O/S front tyre on 300Tdi has worn away. Braking was fine with this tyre on. I have swapped with a new tyre and brakes are now locking in the wet - fine when it is dry. I have just had the tracking checked and it is spot on.
I imagine I am looking at the likes of wheel bearing, bushes or something awry in the steering setup. Any suggestions on where to start?

Incidentally, front tyres are now mismatched pair - would this have a bearing on the brakes locking. I will be putting new ones on this week but don't want the premature wear again. The guy who did the tracking thought it was normal if it has worn over a period of time - but why just the one??