Ive been trying to fix this problum for two years, Ive got OEM wheels and had loads of balance jobs done, put new dunlop tyres on that seemed to make the most differance but it is just slightly still there, so I must agree it must have something to do with the tyres, I think the only solution is to go to Lexus and say put your OEM tyres on please and pay the money see if that sorts it out if not keep going back untill they do.