Shaky A4 HELPP!!!
 

I have a 2001 audi a4 quattro, I bought 18" rims online and had a local shop put them on. In comparison to the stock 16" wheels the new rims are wider as well (about 8.5"). There was some sort of rubbing going on with the tire and the inside of the suspension due to the larger wheels, so I bought spacers to push the wheels out a little.

When the vehicle reaches speeds of 40mph or more the vehicles starts to shake, feels like its bouncing up and down and the steering wheel shakes as well. The shaking gets stronger as the speed increases and usually i feel it more when i accelerate then when i let go off the gas, although the shaking is still there. When i put my stock rims back on the vehicle rides smooth.

I took it to STS for a wheel alignment since I know this could be the cause, but the mechanic said he could NOT align my wheels (??? wtf).

does anyone know why the car shakes wit the rims on?

and why would STS be unable to align my wheels with my rims on?

Thanks for the help or any ideas