Russell,
On Mon, 25 Sep 2006 16:56:42 +1200, Russell McMahon wrote:
{Quote hidden}> I recently discovered in a very niche situation (stupidly overloaded
> vehicle with largish rear bias)(at 2am fwiw) that speed wobbles in a
> car could be instantly corrected by applying a ~ 2 Hz oscillation to
> the steering wheel, approx 30mm movement range on a reasonably low
> geared steering system.
>
> As I don't have vehicles / situations which have speed wobble
> available every day I can't retry this in a hurry. I was wondering if
> anyone else had heard of this "cure" or of how universally applicable
> it was.
>
> Results were "like magic" - at one moment a slowly building (slow in
> this case) oscillation that required intelligent ongoing correction
> and the next moment instant stability. No head shaking or slowly
> coming right but an instant transition to stability.
>
> The friends who I have asked about this all lecture me about
> overloading, which is fine, but fail to comment on the "wobble cure".
I think you may have been experiencing "Pilot Induced Oscillation", somewhat familiar to flyers! :-) Once it started your attempted correction input
was just at the right phase to add to the problem, and doing something to distract you from that (the deliberate steering-wheel wiggling) stopped
that, and it sorted itself out. Did you try letting go of the wheel? That may have worked too! (Or you may have ended up in a ditch...)
Overleading the rear is a very Bad Thing because it reduces steering authority. I was once in a seriously overloaded van (I and two other mechanics
at the garage where I was working had just loaded up a large stack of wet asbestos-cement sheets - it was a long time ago!) and it was possible to
turn the steering-wheel half a turn each way with no change of course at all. The only way to get round corners was to brake, so transferring some
weight to the front wheels. Looking back, I sometimes wonder how I made it out of my teens... :-)
Cheers,
Howard Winter
St.Albans, England
