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Originally Posted by cardnation
How many times do we have to go through this?
IT IS NOT A TIRE ISSUE.
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Tires are clearly involved, (as changing tires can and have sorted the issue), although they may not be the only part of the problem.
It does appear that the problem fits the definition of steering nibble, smooth road shake (SRS), torsion nibble. Definitely discussed in the technical articles on EPAS. This does often involve wheels and tires. Typical causes of SRS, to quote:
Quote:
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SRS is caused by internal periodic excitation such as wheel imbalances, tire irregularities, brake rotor imbalance and lack of precision piloting of the rotating members.
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EPAS typically has some form of active nibble control. Personally I can't see BMW having anything less than state of the art EPAS, but something is not cancelling out the nibble in all cars. There must be some frequency in some cars which excites the vibration. Changing wheel/tires can cancel this out, as balancing has done on some examples. Even mileage on the tires is changing this excitation in some cases.
I suggest BMW will be seeking better control of the excitation and damping/cancelling function, which controls the feedback loop to the steering wheel.
BTW, there are several new patents offering solutions to this vibration problem, in EPAS systems, plus it is clearly not just a BMW issue. In fact the same thing can happen in HPAS systems, and some studies have been carried out where EPAS appears to offer better control of SRS and steering nibble.
HighlandPete