Miata, S13, FC RX-7 OuterTie Rod Interchangability.
 

So miata tie rod ends are expensive, and have some bump steer when even slightly lowered.
The LE oem mazda ones that reduce bump steer are even more expensive.

So I had a plan, be cheap like a drifter and use non OEM parts... from different cars. :lol:
Several of the parts were donated to this cause. Thanks to the people that gave me stuff.

Disclaimer... I have not tried this on the car yet... but I plan to try the s13 rod ends soon.

So first off, a comparison.
Top to bottom:
FC RX7 power steering
Miata (NA 94) power steering
240sx s13.
https://www.miataturbo.net/attachmen...ine=1352097392
And they all fit the others. ( ends swapped one up, inners in same order )
The inners do not swap between racks, they all have different inner threads.
https://www.miataturbo.net/attachmen...ine=1352097392

They angle the outer tie rod for steering feel or something.
The LE/fc tie rods are supposed to reduce bump steer on slightly lowered cars. But I am going to try the dirt cheap S13 rod ends.
https://www.miataturbo.net/attachmen...ine=1352097392

The stock miata one (left) have a large angle, the fc one (right) has less and looks oddly like the LE miata tie rods ends that are really expensive....
https://www.miataturbo.net/attachmen...ine=1352097392
But for slammed cars, the s13 is straight, and all fit fine in the NA miata hub.
https://www.miataturbo.net/attachmen...ine=1352097392


As for price, the s13 is winner too.
Cheapest outers on rockauto:
Miata 1995 $35
Rx-7 1989 $25
S13 1989 $7 :lol:
The LE oem mazda part are $60+ each, and are the same looking angle as the RX-7 FC outers.

Bumpsteer is NOT a function of the angle between the tie rod end joint housing and the tie rod, but of the height offset between the axis of the tie rod and the axes of the control arms as determined by the location of the tie rod axis relative to the pin taper where the tie rod end seats into the steering arm.

Not sure what you call full lock forced steering caused by bumps then.... "the other bump steer"

Not a suspension engineer. Just a drifter, and we be cheap. I like $25 tie rods over $60 tie rods that are basically the same.

I'll just remove my wrong bump steer info.

It's still bump steer, you're just not describing the fix for it. Changing the length of the pin between the pivot ball and the taper is what changes bump steer. Changing the angle of the pad that the joint rides in... changes the angle of the pad. Effectively nothing else. Go read Milliken's Race Car Vehicle Dynamics. Try this thread again later.

Doing some googling. On bump steer aka "reactive toe"
Learn something new everyday, but the more you know about cars, the less you understand about cars.

haha thats the truth

Wont you run into binding issues at full lock with the ball joint being strait rather then angled?

I thought this would help. Because if the wheels moves 1 inch up over a bump when the tie rod is perfectly horizontal at rest the tie rod end would move in slightly, turning the wheel. But if the tie rod was at 45 degrees 1 inch movement would move the tie rod end heaps further in, turning the wheel more. Does this apply more to changes in toe in cornering and braking? Can someone correct me here?

Im just doing thought experiments at 1am in the morning, so Im probably not getting a full grasp of the situation...

Does anyone know what the thread size of the end that goes into the rack is?
Google was not my friend today and was with holding this information from me.

This ^

The joggle differences in the cast part in those comparison pictures don’t change the kinematics of the suspension one bit. the Joggle is just for centering the range of angular movement needed of the ball joint as the suspension articulates. without some joggle you might run out of range of motion and start bending the tie rod if you have too much rebound travel by exceeding its range of motion. This could be a problem with just using a common rod end with an ajustable stud.

What matters for suspension kinimatics is where the center of the ball on the stud part ends up relative to the arm when it’s tightened in place on the knuckle, Is it longer or shorter.

I have personally seen 3 different thread sizes on OEM miata racks even the input splines are different NA to NB. Im not sure if all NB's are the same. Might need some parts book searching to figure out change dates.

An easy way to understand this is to insatall the different joints and measure from the mounting surface on the knukle, to the center of the ball joint. Until that measurement increases in height, nothing will change. Like it was stated before, the angle of the joint is there to allow total movement without binding the joint itself.

Sorry to dig this up, but I need to get my car aligned and figured I might as well replace my tie rod ends with busted ball joints first.

Can anyone dumb this down for me? Did AkaZero just show us that $40 FC tie rod ends are the same as $130 LE/R-pkg tie rod ends? Can I just cheap out and get random autoparts store brand or do I need to get OEM stuff?

I just replaced mine when i depowered my rack. I used the cheap ones. they were comparable to my stockers.

Looking at the car on the ground it certainly looks like the S13 tie rod ends will resolve the bumpsteer issue (as far as I understand it anyway). I went ahead and ordered some so hopefully they work out. I'll try to take some before and after measurements for the angle on the tie rods.

I kinda feel like the s13 tie rods will bind. The knuckle on my miata is at a downward facing angle. I think the tie rod needs a matching angle to avoid binding.

Im really interested in the FC tie rod. It looks like the le one. Has anyone tried it since the original post?


Which cheap ones did you use? Just cheap miata ones? Or one of the optio s listed here?

S13 tie rods arrived and went on. They physically fit but steering is obviously screwed up, very darty and unstable. I wouldn't leave the neighborhood on them. I measured the height of the end of the tie rod and it was actually 1/16th higher (worse) with the with the S13 ends vs stock. Going back to the regular miata tie rod ends, it was worth a shot.

I'm still interested in the RX7 ends, but not willing to keep swapping them out to see if it works.

I think you will have a toe adjustment limit problem with the FC ends.

Thanks for testing this for everyone though. I was interested since getting R/LE tie rod ends are pretty pricey.

The '94 LE power rack ends DID NOT work on my '91 manual rack. I could not get tje toe right with my MOMO wheel. Ran out of thread on the rod.

Just an FYI