[byroncheung]

2011 e90 zcp with stock 359 wheels, Michelin pss tires.
The vibration is pretty minor, but detectable if paying attention. Seems to be most noticeable when it’s at constant speed going straight. No vibration when turning.
I suspect it has always been there, but I never noticed it, until I put on spacers, which magnify it really badly. I checked / fixed the wheels and tires (all four were slightly bent but now they are straightened and well within spec). Now these vibration is in my head now, even without spacers I can still feel and will look for those slight vibration...
It is certainly tolerable, it’s a very slight left/right shake of the steering wheels, if one is holding the wheel tight, probably won’t even notice. But just worry there is something wrong. What can be the possible source? Wheel bearings? Joints?
I think I can rule out the wheels and tires since it is just straightened and balanced. Not rotor warp because braking is smooth. Any ideas?