biggus

In my Chilton manual it shows caster for my 68 Cutlass as 1/2 to 2° -. For king pin inclination it shows 9°. What is king pin inclination, I thought that was for strait axels. If it's just a carry over from the days of yor how do they come up with 9°?

joe_padavano

FYI, the Chassis Service Manual calls it the Ball Joint Inclination angle, which is more correct for a ball joint front end.

The caster angle is the angle of the line through the ball joints relative to vertical when viewed from the side of the car. The kingpin or ball joint inclination angle is this angle when viewed from the front of the car. This is different from camber angle, which is the angle between the tire centerline and vertical.

The ball joint inclination angle is important because it is part of what determines the scrub radius, which is the difference between the point where the line through the ball joints intersects the pavement and the center of the contact patch. The larger the scrub radius, the more difficult the steering force. This is why FWD cars have wheels with a lot of positive offset. The outboard CV joint needs to be in line with the ball joint inclination axis, which pushes the wheel bearing and wheel mounting flange outboard. The positive wheel offset brings the contact patch back towards the car to minimize the scrub radius.

biggus

Thanks Joe. That clears it up. Years ago we played around with designing a zero scrub front end on a stock car. Built several spindles and Arms but could never get clearance for the huge calipers we had to run.