[Huskinhano]

My take on what’s being said is not so much relocating the pin to make the car sit lower but actual height of the spindle itself. My understanding of short and tall spindle is in it’s relationship to the upper control arm mounting location. In a performance situation you want the ball joint pivot location to be higher than the mounting point of the control arm. As the suspension compresses it pulls the top of the wheel in following the arc of the control arm for negative camber gain. In the case of the Mustang it’s not so when stock. To get the negative camber gain you can put a taller spindle or lower the mounting location. It comes down to that relationship of the ball joint to shaft location.

In the case of MM, I see it that he’s using a taller spindle to make the ball joint higher in relationship to the shaft while Shaun has shortened the spindle but has also changed the shaft location to accomplish the same basic idea. To me Shaun has taken it to the next level in engineering. That’s my impression of what’s going on.

 

[Huskinhano]

Kind of. I should have put the disclaimer in my first comment too but I'm not a suspension whiz by any means. Wiring, engine tuning, and tire kinematics i've got down pretty well but chassis and suspension stuff I'm still catching up with. That being said, there's a few things going on from my limited understanding:

Its not just the upper control arm (UCA) that's dictating camber change but also the lower control arm (LCA) or LCA + strut rod in our design. You're correct in that the arcs of these are going to dictate kinematic (moving) camber change but its the difference in them that's the important part. As an example, with the stock-height springs and the LCA in an "OE" configuration, it's pointing down. With the LCA pointing down, the amount of lateral change in the lower ball joint (LBJ) was less than the lateral change than the upper ball joint (UBJ), mainly because of their length difference. That's why moving the UCA inboard points down slightly via the "shelby drop" were able to improve the camber curve for a mostly-stock geometry. Instead of an initial outward movement in the UBJ, it's now an inward movement, so the overall camber change is improved. It's possible to have the UBJ point lower than the inboard point, and still have negative camber curve through travel from static.

The spindle location itself isn't going to have a whole lot to do with any of the above, nor the bump-steer qualities. That's all dictated by the inboard and outboard points of the control arms. It will however change how the forces act on those points which the driver is likely to feel. Additionally, changing the tire centerline via wider tires will affect the scrub radius, which will change how the car feels driving and mainly under braking. Also there are advantages and disadvantages to moving the outboard points closer together. How much of the disadvantages are quantifiable, i don't know, I've not played around with that aspect as much.

Also as an aside as an interesting conversation point, all of the designs discussed up until now are "short spindles", their points all land within the inner wheel diameter. There are designs however like the 350z and 370z that have a "long spindle" where the UBJ lands outside of the tire. Totally irrelevant to the conversation at hand but just an interesting tidbit I thought of when yous tarted talking about long vs short spindles!

350z front geometry:
View attachment 877810

True the lower arm will have some effects on camber. However they’re usually longer arm than the upper arm. It’s arc of travel is going to be far more gradual and less camber changes one way or another. I was just mentioning the upper as the meats and potatoes of it.