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Dean,
You are correct in assuming that if the forces that contribute to road feedback are acting on the kingpin axis the steering will have very poor feedback.
This is why the scrub radius is kept non-zero. It is usually held between -5 and -10 mm. Most of the forces acting at the road surface transmit through the base of the tire. Scrub is the important quantity there.
If the mercedes that you were speaking of had a scrub radius of zero, that would be a very numb feeling suspension.
Torque steer is dependent upon spindle length. I fudged my first response a bit because I was trying to keep things simple. Without a picture it is hard to explain, but I will try. You might want to draw one as we go through this...
Imagine for a second a driveshaft that is horizontal. The input torque will be horizontal and we will call it "T". The vertical distance from the center of the wheel to the ground we will call "R" The kingpin inclination we will call "KPI". The Scrub radius will be "SR"
To sum moments about the King pin we need to break up the horizontal input torque into two components. One will be perpendicular to KPI, the other will be parallel. The parrallel component will be "T sin (KPI)". That is the component of the drive torque that tends to yaw the wheel. The other component of the wheel yaw torque will be the force at the wheel times the scrub radius. "(T/R)*SR" Adding the two components we get the total yawing torque of the wheel to be "(Tsin(KPI)+(T/R)*SR) Rearanging the terms we get "(T/R)*(Rsin(KPI)+SR)" Equal to the yawing moment of the wheel. Using small angle approximations for KPI, Rsin(KPI)+SR is equal to the spindle length. So if the spindle length is zero there will be no torque steer regardless of torque balance from left to right. (assuming the tire transmitts forces at the horizontal center)
Road feedback will be maintained because it comes primarily from forces originating at the road surface. Those forces times the scrub radius will generate the wheel torques that cause feedback.
I am not sure I understand your question about "how camber affects where a wheel wants to go?" If you clarify it a bit I hope I can help you out on that one as well.
, Sat, 2 Dec 2000 13:18:01
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