At speed of 60 - 70 mph, the steering wheel wobbles. When below 60 or above 70, the wobble dissappears. Wheel balance has been checked, as has steering column, but nothing found that could explain the cause. All but 3 tyres have pressure sensors fitted, 1 missing from the front. Could this be the cause? OtherwiseI dont have a clue as to the cause. Can anybody offer any explanation as to the cause? Thanks