[BimmerGuyFL]

Hmmmmm this is an interesting topic. Previous Generation BMW's suffered easily from this same problem. The E39 5-series from 1997-2003 was notorious for this. It could be that when they switched from the E90 platform to the F30 platform, in an attempt to make the ride quality smoother and more absorbent, that the front control arm bushings are softer. Therefore giving the control arms more play (shimmy) in that vibration frequency (40-60mph). The E46 had pretty soft bushings and it rode better than the E90 but a lot of the times these bushings had to be replaced cause since they were softer it would absorb impacts more at the bushing instead of transferring it through other components. By 25K thru 35K miles a lot of E46 needed bushing replacements. When the E90 was released I remember reading that the bushings were stronger but not as absorbent as in the E46 which caused the E90 to have a firmer ride, yet most E90's never had this SHIMMY at the steering wheel problem in general.

So.....IMO I would say that the problem lies at the front lower control arm bushings not being strong enough to keep the car from shaking at those speeds.