@forestg posted:Pitman arm??
The spindle steering arms. Sorry having a bad day. Covid booster shot 48 hrs of Hell. Still some fog to clear yet.
You are rotating the spindles by increasing the castor and that means the steering arms/tie rod connections are going up.
That could be helping the bump steer but I doubt that?
There is only one way to know.
You have to measure the change in the steering as the suspension moves up and down BEFORE you make the changes, then again AFTER you make the changes.
Often you will need to readjust the length of the rack steering arms (shorten) in order to get the 3/16" toe in.
By doing so you are changing the arc of the steering arm/tie rod end connection point and you may be creating a greater travel outwards during the swing through the arc which is the definition of bump steer.
Increasing the + castor sounds simple but it is not. You need to keep the wheel/tire centered in the fender and you can't increase or adversely affect the bump steer.
Dillara's original design is good. I never measured the Pantera for bump steer. It isn't a simple thing to go and do casually.
Certainly radial tires help the situation. Bias plys increase the sensitivity negatively.
IF you could show me the original design and it indicates a design of +6°, not +2.5°, then I will agree with you wholeheartedly and say do it and blame the +2.5° on Ford, but everything would have to be as the original specs including the originally specified rack and mounting. You can't modify from that. Even the design ride height is involved.
I've done the Shelby 1" drop on Mustangs and I can tell you that the bump steer is increased dramatically.
In my view it is so severe that the tie rod ends connection points need to be modified with 1-1/2" cnc steel billet blocks to make the car driveable.
This also has to do with castor change since in that case happens to increase it at certain points through the suspensions travel through the arc.