Hie everyone

I have an issue with the Mustang II spindles.
I am trying to design my own crossmember and a-arms based on MII spindles and rack.

According to the theory to accompish "zero" bumpsteer the inner and outer balljoints has to be aligned. I have aligned the inner ones without trouble according to attached picture. However when I modelled the spindles in 3-d it showed that the steering arm balljoint is slightly of this align, I assume to accomplish better ackerman see pictures in my gallary.

The red cross bellow the steering arm on the spindle picture represents the balljoint centre. See pictures in my gallary.

Is this a fact with all aftermarket MII spindles or what. I find it impossible to align the outer balljoints when the spindels lookes like they do.

Is this in fact a compromise between ackerman and bumpsteer?????

Anyone????

 

Hi

Not sure what you mean by inner ball joints. I'm going to guess you are talking about the control arm pivot points. I would think you need to do a full model showing full jounce to full rebound and full lock to lock turn. Which will include your inner and outer rack pivot points. You may have to change the rack location and/or the arm length.

I would also have my tire info and some of the frame just to make sure you don't hit anything in full turn (should also have part of the fender both inner and outer).

You should be able to watch it as it's run and see how much if any bump steer you have with this design.

All design work is somewhat of a compromise.

Chuck

 

Hie

Yes I did mean the inner pivot point of the control arm. I have some problems with my gallery so I cant post any more pictures.

However I have made the complete suspension modelling in 3d and everything is ok accept the design of the MII spindel. As the spindel is design from factory it will not be possible to line up the outer tie rod en with the outer upper and lower balljoint. is off by approx 0,66" no matter what I do. If I want to modify the spindel steering arm so that the tie rod end lines up with the balljoint (heating and bending) then the ackerman angel will be zero. Or ??????

Am I totally out in the blue or what.

 

If I understand correctly it would seem to me if you are thinking of moving the tie rod point inboard towards the center of the vehicle you may be inviting more bump steer unless you move the steering rack inner point inboard also. One other thing my moving in the steering (tie rod attachment point) point inboard you may end up with it moved forward and vertical (up or down) in other words it is a very good possablity that it will move in X,Y and Z. I'm not sure that you can heat and bend the arm.

If you have a suspension program that you can apply to this model run what you have then move the steering point on the spindel and run it, then try one with that mod and move the inner point inboard on the rack (to match the length of the first arm) just to see what effect it has on the steering.

You may find you are in the ball park now.

Nice job

 

Hie again, thanks for the feedback

I really dont want to modify the spindel, it doesn't feel safe. I have tried to lower the rack i.e. the inner pivot of the rack goes outwards then the pumpsteer gets really close to zero but then the ackerman becomes ****ed up so which on should one focus on ????

Best regards Jimmy

 

yes, the steering arm pivot point will not line up with the lower ball joint due to the ackerman designed into it. the ackerman is much more important to drivability and tire wear that the tiny amount of bumpsteer you'll get from that misalignment. It would be a near impossible task to design a suspension geometry suitable for the amount of travel required for street use without comprimise someplace. Since hitting something that would cause bumpsteer would cause path deviation anyhow, drivers don't notice the bumpsteer effect portion as long as it is not significantly large.
The inner rack pivot lining up with the inner A arm pivot side to side and both the A arm and outer link being close to parallel with the ground is much more critical and will require a rack extension in this case. Don't forget to design in some camber gain and anti dive while you are at it. Race Car Vehicle Dynamics (I believe that is the correct title, my copy is at work) is the "bible" of high performance suspension design theory and practice. Might check a engineering university library for a copy, it's rather expensive to buy, and gets pretty deep into higher math.
PS, the designed in ackerman of the MII upright will also end up being a comprise because of the change in track width and wheelbase length.

 

Thanks AXracer.

Thats exactly what I have been struggling with. Do you have any idea of how much off the ackerman is due to the wheelbase and track with difference.

Best regards.

 

Can you or someone else enter all your suspension info into a suspension program and run your model. That will give you a nice visual of what you really have.

 

Actually Merc546

I think´I have something better than a suspension program and that is ProE 3d-cad system where I can change, modify, specify and measure anything I want. Unfurtunatley I have some problem with my gallery and cant post the pictures I want to show you.

Thanks anyway

Best regards Jimmy

 

A suspension program will show more than a 3-d cad program will since it will show the how the entire car will react/interact to things like spring rates, static and dynamic roll centers, swaybars, etc.

 

To correct bump steer you need the inner pivot point of the rack to fall on a line drawn between the rotational points of the upper and lower control arms. You must also have the tie rod running parallel to the lower control arm at ride height. That will be as close to -0- bump steer as possible.

SPark

 

Yeah, "Race Car Vehicle Dynamics" by Milliken and Milliken is a good book to reference for these kind of questions, but as stated, it gets real heavy real quick. You can usually pick up a used copy on ebay or a college bookstore site for 60 bucks or less and its well worth it. The other standard in vehicle suspensions, by Gillespie (sp), isn't nearly as good, so don't waste your money (I don't remember the book's name).

WinGeo by Mitchell (http://www.mitchellsoftware.com/prod01.htm) is also a pretty sweet program to mess around with this kind of stuff. You can do all kinds of iterations and it'll spit out graphs and numbers for all parameters. $500, but it'd probably be worth it if you ever plan to do more suspension work. It pretty technical and has a pretty steep learning curve, but at least it's a cool program. If you PM me I might be able to send you an older version of the program.

 

Tune to Win, Engineer to Win, both by by Carroll Smith are essentials and great bargains @ ~20.00 each in paperback. Carroll was a master of race car engineering and also had a knack for putting what he knew into words that made the theory and practice clear and easily understood by the layman, while cutting out the BS and debunking the old wives tales at the same time. Highly recommended for anyone wanting to know about what happens when the "rubber meets the road" and how to make it work better.

 

Hie everyone

And thanks for all the feedback. I have read the tune to win by Carrol Smith good book no question about it!

I think I have to see if I can find a suspension program to see if I can get the hang of it, I might learn somthing.

Regarding the bumpsteer. I lowered the rack so the inner pivot point got slightly miss aligned with the upper and lower inner pivot points, in the same way that the outer steering pivot point is missaligned and the result was great very close to zero bumpsteer.

Is this a ggod way to go or do you have any opinion regarding this way to proceed.

Best regards Jimmy

 

The ideal situation FWIU, would be to have the rack pivot and the A arm pivot the same distace from the vehicle centerline and the tie rod and control arm be parallel to each other and level with the ground. Unless the spindle arm is in an unusual place the two pivot points will not align vertically. A small misalignment is not critical, we don't drive on a billiard table anyway. Even the best racing surfaces are not smooth and flat.