A time-related reason why the originally specified caster is now too little is a result of changes in tire configuration over the years since PVs were designed and sold with narrow, high-profile bias-ply tires.

Part of the self-centering steering effect of caster comes from the deformation characteristics of the tire carcass and tread, where the effective center of tire contact with the road moves rearward as the car rolls. The rest of the total camber effect comes from the actual suspension alignment.

Radial tires have less camber-like tire contact patch "trail" than did the same nominal size bias ply tires. Lower profile, wider radials have even less.

Thus more caster has to be provided in the suspension parts (ie, more lean-back of the kingpin toward the rear of the car) is needed to keep the rolling tire contact point trailing the kingpin centerline's intersection with the pavement to provide a happy behavior.

Thanks for offering your experience with adding positive camber. What size and type of tires are you using with this one-turn camber increase?