Zink Z12/18 steering setup

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BLS
Posts: 441
Joined: May 11th, 2011, 7:52 pm

Zink Z12/18 steering setup

Post by BLS »

As I rework the old Zink, I'm trying to figure out a way to increase the legroom without making modifications that significantly modify the original design. I could fabricate a system with the steering arm facing forward like I remember the later Zink/Citation designs. This appears to be easy enough while allowing for a return to the old system in the future. The front beam mounting blocks can be modified to add a lever arm on each side to transmit the steering motion from the front to the back very similar to what I remember on the later Zink design. This would free up another 6 inches or so of space.

What I also remember is that I did not like this design as it appears to be very high on bump steer due to the very short length of tierods from the lever out to the wheel. OTOH, those cars seemed to be pretty good at the time. Maybe there is something I do not understand about the design that minimizes the effect? I do understand how to manipulate the effect with the tierods level/up/down. Maybe it just doesn't make that much difference?

In any event I know there are other cars that use something similar. If anyone has any advice or thoughts please let me know.

Thanks,
Barry
Barry
Old Zink FV,
'87 Citation
Bob Posner
Posts: 70
Joined: January 23rd, 2008, 7:35 pm

Re: Zink Z12/18 steering setup

Post by Bob Posner »

Post this on Apexspeed to get a reply from Steve Lathrop who designed the system.
brian
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: Zink Z12/18 steering setup

Post by brian »

I agree with Bob regarding catching Steve on the Apex forum. The bell crank steering designed by Steve had very little bump steer given the fact that the tie rods were short. The secret is that the tie rod pivot point at the bell crank was located along the radius line of cone created by the steering pickup point at the wheel. Since it lay on the radius line it simulated a much longer tie rod. The Caldwell D13 rear trailing arms accomplished the same trick by curving the arm into the frame rail at the roll bar, thus simulating a much longer trailing arm. Neat stuff.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
BLS
Posts: 441
Joined: May 11th, 2011, 7:52 pm

Re: Zink Z12/18 steering setup

Post by BLS »

Thanks for the reply's. I'll post on apex as well.

Brian, I had not thought it through very much, just thinking about it last night. What you said makes sense. I'll look at it again this evening and see if I can figure it out. It would certainly solve the problem of increasing my legroom without making major mods to the frame, so I hope it will work.

Thanks,
Barry
Barry
Old Zink FV,
'87 Citation
SR Racing
Posts: 1205
Joined: June 24th, 2006, 1:58 pm

Re: Zink Z12/18 steering setup

Post by SR Racing »

Brian is correct. The radius angle of the bell crank system was designed to limit bump steer. It worked pretty well. We are almost complete with another FST car (converted XTC) using the bell crank steering with a rack, exactly for that reason.
jpetillo
Posts: 759
Joined: August 26th, 2006, 2:54 pm

Re: Zink Z12/18 steering setup

Post by jpetillo »

I'll third what Brian said, and that lever system has very little bump steer, by design! The length of the tie rod is not what gives or prevents bump steer. John
BLS
Posts: 441
Joined: May 11th, 2011, 7:52 pm

Re: Zink Z12/18 steering setup

Post by BLS »

Jim, John,

Thanks for the response. I *think* I understand it now. I was thinking of it with a tierod parallel to the front beam which would cause bump steer. I can see how to cancel out the bump steer with the arc the tierods make matching the arc of the trailing arms as close as possible. Something like that anyway.

Thanks again,
Barry
Barry
Old Zink FV,
'87 Citation
problemchild
Posts: 901
Joined: June 25th, 2006, 9:34 am

Re: Zink Z12/18 steering setup

Post by problemchild »

Barry,
The placement of all those pivots, links, etc is very critical. When its right, bump steer characteristics are excellent. When wrong .... its nasty!
If you are looking at adding footroom, most people these days seem to go with the inverted steering box behind the dash. Much simpler, fewer parts, and pretty good performance.
Check out pictures of Womers for more info.
Greg Rice
"Happy 50th Birthday"
BLS
Posts: 441
Joined: May 11th, 2011, 7:52 pm

Re: Zink Z12/18 steering setup

Post by BLS »

Greg, thanks for the response.

The Womer style is what I would use on a new car. However, it would require some chassis mods to the old Zink that I do not want to make in order to preserve it. I can make the mods using the Citation style without damaging the car as the front beam mounts allow me an opportunity to fabricate the lever to make it work. This way only those beam mounts get changed. I've spent some time discussing this today, and with help from the forum here I think I have a good handle on the design criteria. I made a drawing this evening and it looks doable.

I've got the car apart and down to the frame for modification and repaint. I'll add the forward roll bar bracing and then work on the steering. If I can work it out I'll post a follow up here.

Thanks again,
Barry
Barry
Old Zink FV,
'87 Citation
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