Ok an update.
I put my old wheels back on, the standard turbine alloys with 225/55/16 all round luckily I haven't sold them yet.
Then went on the motorway and cruised at 70mph no problem it was as smooth as silk as you would expect from a BMW. So this eliminates any problems with the cars suspension, control arms, bushes, cv joints, springs, dampers etc.
It cant be the alloys cause there brand new got them 3 days ago and I saw them beeing assembled out of the box they came in and the tyres are brand new as well.
And I've had it balanced twice first time when they assembled the wheels and second time when I took it the a local garage.
So next port of call. Can anybody recommend tyre pressures for 235/40/18 and 265/35/18 I got a sneaky suspicion that they are the same all round. I've looked in the car manual but it only gives figures for upto 17".
If that fails then the only problem would be the lug nuts. My car is 1999 reg which I think, might of used heavier lug nuts back then than they do today. And cause I'm re-using my old locking nuts ( saves me having to pay for another set ) which originally came with the car, there mixed with the brand new lug nuts that came with the wheels. Which could be chucking the wheels off balance.
So when I get some tyre psi figures I'll try that, then if it doesn't work I'll put on my old lug nuts.
Thanks in advance.