Bump Steer / Rack and Pinion

S

Sensei

Member
Joined
Mar 30, 2008
Messages
5
I am gathering parts and information in preparation to fab my own '92 Grand Am rack and Pinion conversion.

My question is about bump steer. My understanding is, you want the tie rods to run parallel to the lower control arms so their arc of movement is together, right?

I have the stock gymkana suspension and 255/60R15 tires. It looks like the stock orientation of the tie rods is ideal (you would think it would be). So, can I just fab a bracket to go on the rack and pinion that would reach to the stock location of the tie rod ends, and just hook the stock tie rods to it without modifying them?

This is my steering I'm dealing with, so I need to get it perfect the first time. Thanks for any help.

God bless, Sensei
 
Okay, I understand the diagram and can see that parallel is not what you want. But if GM designed things right, the stock inner tie rod end location should still be ideal, right? And would there be any problem with a bracket that just hooked to the tie rod ends at that point and bolted to the rack and pinion in the center?

Also, just a comment. I was over at Gene's (MrVette) house the other day looking at his set up, and he had fabbed tie rods that went all the way to the center of the rack. His inner tie rod ends are nowhere near on line with his control arm pivots. It seems that would not work well, but he has been happily driving the car that way for years.

I'm just trying to be sure I understand all this so I feel confident I am doing it right.

God bless, Sensei
 
Sensei said:
Okay, I understand the diagram and can see that parallel is not what you want. But if GM designed things right, the stock inner tie rod end location should still be ideal, right? And would there be any problem with a bracket that just hooked to the tie rod ends at that point and bolted to the rack and pinion in the center?

Also, just a comment. I was over at Gene's (MrVette) house the other day looking at his set up, and he had fabbed tie rods that went all the way to the center of the rack. His inner tie rod ends are nowhere near on line with his control arm pivots. It seems that would not work well, but he has been happily driving the car that way for years.

I'm just trying to be sure I understand all this so I feel confident I am doing it right.

God bless, Sensei
Click to expand...

Chris, it was better than stock in SO many respects, that I didn't care much about any bump steer, when it got to be a 'hot' topic Norval did his suggestions, but by then I had the rack in place....Pete79L82 (I think I have his handle right) said to raise the inner rod end pivot points some 2" or so....

so I cut off the ears and flipped them upward via Johnny's welding....
 
There are 2 ways to go about this, if you want to use the instantaneous center you have to follow the diagram, this is the most precise method. You can also make the rods as long as possible. This is what GM did for the C4 rear control system. The thought here is, with the long rod, as the suspension goes through it's deflection the rod angles less than a short rod, and as such the angular effect on the horizontal vector component is less. Simply put, when you raise a long rod an X amount on one end it will make less of an angle than a short rod. This is simple vector stuff.
 
Twin_Turbo said:
There are 2 ways to go about this, if you want to use the instantaneous center you have to follow the diagram, this is the most precise method. You can also make the rods as long as possible. This is what GM did for the C4 rear control system. The thought here is, with the long rod, as the suspension goes through it's deflection the rod angles less than a short rod, and as such the angular effect on the horizontal vector component is less. Simply put, when you raise a long rod an X amount on one end it will make less of an angle than a short rod. This is simple vector stuff.
Click to expand...

NOW that you say it, I remember some words to that affect, and so I didn't feel so bad about my long tie rods anymore....

now having said that, my install is not perfect...but I feel anything I do to make a slight improvement is going to be not worth the effort.....

then again, I don't race....just drive quickly....

:friends:
 
I've been looking at my existing set up. My car is not lowered and the suspension/ steering / wheels and tires are all the stock gymkana set up as it came from the factory. It looks like the outer tie rod ends line up with the ball joints, but the inner ends are an inch or so inboard of the point at which they would be in line with the inner "A" arm pivots. So while the rods are not really long, they are slightly longer than what is shown in the drawing in Twin Turbos tech article. I guess what I really want to know is, would using the stock tie rods unmodified and making the center bracket to reach out to hook up in the original location a good idea?

Also, just another thought as I try to get a solid understanding of all this; all of this stuff about the proper geometry of the tie rods to "A" arms seems to assume the car steering is set straight forward. It seems to me, as soon as you turn the steering wheel, the alignment of the outer tie rod ends to the "A" arm pivots is lost. Am I right, and if so, is there a compromise built into the system to allow for that, such as the tie rods being a bit long so they come into alignment with the "A" arm pivots on the outboard side of the vehicle during a turn?

Thanks for the edcucation, Sensei
 
You must log in or register to reply here.
Top