Wilwood ProSpindle and bump steer

[feeble]

I'm sure Wilwood more or less duplicated (except for the height) the Mustang II spindle geometry but shouldn't the ball on the tie rod end be on the line drawn between the upper and lower ball joint as shown here:

https://static1.pt-content.com/images/pt/2012/06/ZeroBumpSteerPositiveoffsetnegat1-1.jpg

On the frame side of the suspension, I have as shown in the above illustration, but this is what I have on the spindle side of the suspension.

https://static1.pt-content.com/images/noimg.gif

As you can see, the tie rod center does not lie on the ball joint axis.

If the top illustration is correct, can I get where I need to be with a bump steer kit or should I make a new arm? Since the arms bolt on, any chance Wilwood would make new arms that address this and offer it as an option? Art Morrison uses these spindles on some of their kits, do they replace the arm or ???

Thoughts?

[SLO_Z28]

One option would be to make a new steering arm, but that will change the ackerman. I would measure what the current ackerman is and see if more would be beneficial.

[feeble]

Or would it more correct to say that the ball joint balls and tie rod ball should all lie on the same arc whose center is the instant center?

[CA B4C]

You are the right track. The difference between the upper and lower ball joint line and the tie rod mounting point creates your Ackermann.

When the tie rod end points line up with the instant center you minimize bump steer.

By the way, nice CAD work !!

[feeble]

So... if I understand correctly, I only need to have the inner and out tie rod pivots line up with the instant center (but don't necessarily need the outer on the same axis as the ball joints) and my bump steer will be minimized. I only need concern myself with the tie rod ball offset from the ball joint axis if I want to adjust the Ackermann.


Is that correct?

Thanks for the compliment on the CAD, I'm getting pretty close to having the whole suspension (F & R) modeled up. Really itching to start building as I have all of these parts sitting here.

Edit: Clarification

[SLO_Z28]

The entire tie rod needs to pivot on the the same axis as the steering axis to have no bump steer, moving the steering arms pick up point more toward the inside of the car would place the outer pick up point in an ideal location for bump steer, and then the inner pick up point would determine the arc that the tie rod travels in and whether there was bump steer or not. Moving the pick up point of the outer tie rod end will change the ackerman angle, which is toe out per steering angle and beneficial to tune in racing.

[keithq69]

To make sure that you have proper Ackerman you should draw a line from the tie rod when viewed from above, through the ballpoint center line and the line should meet the rear axle at the centerline of the car.
That's why a front steer car will have the tie rid outboard if the balljoint and a rear steer car will have the tie rod inboard of the balljoint.
That's what I've always thought anyways. I'm no suspension designer so maybe someone else can chime in.

[silver69camaro]

Since the arms bolt on, any chance Wilwood would make new arms that address this and offer it as an option? Art Morrison uses these spindles on some of their kits, do they replace the arm or ???

Thoughts?

The steering arms are cast and the tooling along for something like that would be $15-20K, so it wont be worth their while to make new arms. Like you said, the spindle is supposed to interchange with Mustang II spindles with the exception of the height, which improves the geometry.

We do use the Pro Spindle, but the entire suspension was designed around this it (not the Mustang II). While the steering arm does place the rack somewhat high, getting the rack lower leads to many packaging issues. Also, having the tie rod outboard of the KPI on front view helps ackermann and allows a longer tie rod length.

[MCB Matt]

You are the right track. The difference between the upper and lower ball joint line and the tie rod mounting point creates your Ackermann.

When the tie rod end points line up with the instant center you minimize bump steer.

By the way, nice CAD work !!

X2....well put!