OK Guys, so this post is based on balancing the 18" ALU65 rims if like me you've been getting serious steering vibration over 65 mph. It does also apply to other sizes but the 18"'s do seem problematic. After months of trial and error I finally came to the following conclusion:-
1) Make sure the pressures are at 35psi all round first.
2) Have both front alloys rotated with the rears first to see if the balancing transfers from the wheel to the seat of the car, if it does then one of your wheels is out of balance. Or in worst case scenario either a buckled wheel or the tyre needs removing and refitting to the wheel.
3) Where possible you must go to a garage that uses the Hunter GP roadforce machine. A simple wheel balance may not show up any balancing issues as the ALU65 seem to be very sensitive when balancing.
4) Absolutely necessary! Make sure you ask the garage to remove the magic balancing! Magic balancing is a technical term for saving money! It's a way of saving wheel weights and it is absolutely necessary your wheels are balanced with all the required weights.
5) Make sure you ask for road force balancing - this runs a series of high speed balancing tests.
6) The latest hunter GP machine uses a laser to pinpoint the exact place where the wheel weights need to be applied on the back of the wheel.
7) Where possible go to a garage that lets you stand in the balancing bay, even talk to the guys and listen to what they say.
8) Take the car for a spin and see if it improves, don't be afraid to go back to the garage as they should want to help as it's there job to fix, after all you've just paid for balancing.
My local garage balances Aston Martins from Stratstones - I've seem them there. So tbh if they are trusted to balance high performance cars then I'm sure they know what they are doing. The guys here are brilliant. Here's a link to my local garage if you are nearby and are curious - http://www.buckleytyre.co.uk/Wheel-Balancing.asp
I've also seen Tony from Wheels in Motion based down south being experts so if you are near to him then you are very lucky!
If you want to get to the bottom of wheel balancing then don't take the car to a garage that asks you to sit in a waiting room - you need to be involved.
All in all if you to a garage that fobs you off about points (4) & (5) then walk away and find somebody who knows what they are doing. I learnt once when I went to Kwik Fit and asked them to roadforce my winter tyres - they looked at me stupid lesson learnt.