Help - need Miata upright outer tie rod end for 5/8-18 (L/H)

[nisseven]

Hi Redbull
The design of that bottom arm looks very nice, but could you not get the lower shock mount out nearer the ball joint? I am using the Mazda steering rack with the same geometry as the car so there will be no need to shorten the rack and can use the correct tie rods. As they are thinner in cross section this will help with the clearance issue between them and the bottom wishbone.
Bruce

[redbull]

“…but could you not get the lower shock mount out nearer the ball joint?...”
Nope, the constraint in my case is the upper control arm (UCA). I made a “Y” shaped UCA so I could have adjustment in all three (rod end) attachments. This limited clearance of the shock / spring. I have to bump-up my spring load because of the 45 degree shock angle (not something I particularly like). If you are fortunate to have a mandrel tube bender, you could use one of the UCA in a “J” shape, leaving the other arm straight. This allows a LOT of shock / spring clearance and you could place the shock mounts closer to the lower ball joint and the upper mount could be more upright (a preferred set-up).
Also compounding this issue is the extended track (+2” longer than OEM Miata front track)
The Koni shocks are 14” (fully extended) and 4” of travel (3” accounting for spring bind) The higher value spring shock coils take up some room too so I upsized 2.5” to 3”.
I will be adding a brace-bar across both upper shock mounts to keep frame distortion minimalized.
“…clearance issue between them and the bottom wishbone…”
Because you are using the Miata steering rack, you may need to accommodate more than the clearance of the steering rod (to LCA). The issue of “Bump steer” was something I wanted to eliminate, so I opted to go with a configurable rack and pinion (Woodward) so that my LCA and UCA pivot points line-up exactly where the steering rack pivots to the tie-rod.
Bump steer can me a challenge to find the ideal set-up. I also had to raise my rack to the exact position where the centerlines of pivots match AND the rod end height on the upright.
The standard 4130 swag rod end tube clears the 1” LCA (wish bone) fine. At full droop and max turn, it barely touches (and I will not be able to do that once the suspension is loaded anyway).
Setting up the front suspension was a real learning curve, but I am glad I invested the time to understand before I just welded it together. My next build will incorporate inboard shocks because I really want as wide a track as I can and the smaller tubes will allow more clearance.

[nisseven]

Thats a very good explanation and will have a look at how my setup will work with the same Y UCA as that was the way I was tending to go. Regards the steering rack pivot points, I have carefully caculated where they will go and should not have any bump steer. It has been sujested that the MX5 upright needs around 10deg caster which helps the issue of clearance between the LCA and tie rod. I also suspect that my LCA is shorter than yours at 350mm which will help my shock position and angle. Will post some photos when it is done as I am working on the jig now.
Bruce

[redbull]

Ohh that's a lot of caster, I used 6 degrees and that falls within the 5.5 degree "normal". If it gets too steep you will need a low ratio or power assist to turn the wheel when at rest! Depending on the height of you bump adjustment and the thickness of the rod, and the angle of rotation, and amount of droop and bump, and… yes, this never seems to end! Reached the extreme because of my extended track and “Y” shaped UCA.

[nisseven]

Hi
Regards the caster that seems to be the figure sugested by many on this forum who are using the MX5 upright? maybe it is to much?
Bruce

[redbull]

Well, too much caster really make low speed turning tough, but offers a lot of Ackerman if the steering rack is placed closer to the kingpin (back). I measured the MX-5 when it was on the char, and I determined 6 degree, but hay, this is your car... make it the way you want it. When I use to make racing bicycles, the head-tube steering and rake would change a bike from "nervous and quick" to slow, sluggish and stable. So I made my caster adjustable (+/-) three degrees (because I have a “Y” UCA)
Getting all the geometry understood and mocked-up and them fabricated is a “head trip” but I have seem way too many cars suffer from poor front-end geometry to just randomly weld-in the brackets and “A” arms. BTW do not forget rim size and offsets and tyre sizing especially making sure it does not strike the UCP or LCA