ETA: whatever mine is I would like to see how an increase in caster angle improves the weak self centering action, not helped by low gearing on my car. With power assistance steering is over light anyway.
Richard, I know from experience that the rack adjustment is very sensitive and will affect the self-centering. Maybe something to consider.
Thanks Rog although my car has the symptoms I previously described from new and they haven't changed in 15,000 + miles. Interesting that Jon describes the same above. Seems a higher geared rack would improve matters two fold, by reducing steering input whilst increasing self centering action. The standard electric assistance would comfortably keep steering effort under control at parking speeds.
