Quote:
Originally Posted by HighlandPete
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:
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
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My point is, the tires/road force balance may reduce the issue to a point where it is not perceivable, but that does not address the root problem.
No (street) car should be that sensitive to require a 100% 'perfect' tire/balance.
How many cars in your lifetime can you say with conviction that the tires were
always 100% balanced?
Until two months ago, my answer was ZERO. Now I have a set of wheels/tires that are 100%, having been road force balance on two totally different machines.
In the end, this did nothing to cure my steering oscillation and actually they are worse on some road surfaces than my factory wheel/tires.