Pete: Positive caster is when the upper ball joint is to the REAR of the lower ball joint. Think motorcycle or bicycle front wheel. It leans to the rear, that is POSITIVE Caster. If you turn a bicycle front wheel from side to side, it will raise the handlebars when the wheel is turned either way from straight ahead. The weight of the bicycle tries to keep the front wheel straight. An automobile works the same way. Lean the front wheels to the rear and the car resists turning either way, thus it has better straight line stability.