Steering wheel shaking

Hi l200 series 6 with davanti a/t tyres 265 60 r18. Getting steering wheel wobble at motorway speeds. Had the fronts balanced but no better and also swapped fronts with back and still does the same. Starting to think its the all terrains that may be causing it but they aren't aggressive tread patterns they are almost road tyres. Anyone had a similar issue and found the cause? Also had it checked for play in bushes etc but no obvious problems. Thanks