Increasing steering axis inclination on '88 front suspension

[Series8217]

I have a design in my head for a fully adjustable knuckle with shim adjustments for steering offset, stering axis inclination and Ackerman geometry...

Because of my desire to completely rework the 84-87 front geometry in The Mule, it will be a while before I design anything for that car.

However, I could design a set to replicate the stock '88 geometry easily. Would you like the prototypes?

Possibly. I think I'm going to pursue adjustable upper control arms first. Let's give it a couple months and see what materializes.

[Series8217]

I drove a friend's E46 M3 today, and also got a chance to put it up on the laser alignment rack. The front suspension had 6 degrees of caster and 17 degrees of SAI. Holy crapola. It's a strut car with camber plates running 3 degrees of camber in the front. I guess that's what happens with struts in front. It's no wonder those cars aren't good at autocross.. with how tightly you have to turn in an autocross, that static camber is probably meaningless with all the SAI they have.

[The Dark Side of Will]

BMW has to keep the steering rack low to fit under the engine, which means they have to keep the inner ball joints low to avoid bump steer, which means they have to get whatever camber gain they can get from SAI.

So stock it would "only" have had 14 degrees, which isn't too out of the ball park for a strut suspension.

[Series8217]

My front tire wear has been less than ideal at the track and autox, so I'm going to look into making some adjustable control arms first. I can get a few more degrees of camber and some more SAI or caster too.

What taper do the Fiero's upper ball joints have?

[bse53]

I thought I would resurrect this thread, since it pertains to my effort to increase the camber and camber of my autocross car.

At static height, I measured -1.625 negative camber and 6.625* caster. But the increased angle of the mounting points puts the suspension in a bind. I can get less then 2" of wheel travel. This was apparently happening last season, though to a slightly lesser extent.
So I'm back to another idea Will had, moving the mounting points farther rearward. I calculate I'll have to move the mounting point rearward about 1" to create 6* of caster.
The adjustable UCA is the better choice, but I've got a limited amount of time before the autocross season starts.

Brian

[bse53]

Given the stock mounting points and the chassis lowered so the front subframe is at 5", I measured the camber gain at 20* in and out at statit height, 1.5" raised and 2" droop.

static height- 0* steering-- 1.625* camber; 20* steering in- -4.25* camber; 20* steering out- +2.5* camber
1.5" (approx) raised- 0* steering- -3.25* camber; 20* steering in- -6.375* camber; 20* steering out- +.825 camber
2" droop- 0* steering- -.5* camber; 20* steering in- -2.5* camber; 20* steering out- +3.25* camber

[Series8217]

At static height, I measured -1.625 negative camber and 6.625* caster. But the increased angle of the mounting points puts the suspension in a bind. I can get less then 2" of wheel travel. This was apparently happening last season, though to a slightly lesser extent.

Interesting.. What is binding? I don't see how the upper control arm settings can cause any suspension bind, but apparently I've missed something.

BTW I'm running -0.9 camber and 9 degrees of caster on 100% stock adjustment.

[fieroguru]

I have seen the sway bar rub the tie rods on a lowered fiero before (wrong end link length), but aside from that there really isn't anything that should be binding.

[Series8217]

I have seen the sway bar rub the tie rods on a lowered fiero before (wrong end link length), but aside from that there really isn't anything that should be binding.

Yeah, this is a thing mine does at full droop, but I think I confirmed it was OK at ride height.

It shouldn't be affected by alignment settings though.

[bse53]

It's not the ARB. I thought at first if was the LCA, but when disconnected, the UCA rotates freely. Hook it back up to the hub and it binds.
I'm making the spacer to move the mounting points rearward by .8" and raise them 1". That will give me a static camber of -1.0* and 6.25* of camber or more. But I think that's a good place to start.

How did you get 9* of caster and 1* of camber? The most I could get was half of that-- 5.0*, which could be divided between caster and camber.

Brian

[Series8217]

How did you get 9* of caster and 1* of camber? The most I could get was half of that-- 5.0*, which could be divided between caster and camber.

Except for the lowered ride height due to chopped springs, my suspension was stock when I measured this:

Code: Select all

Front           Left       Right
-----
Camber          -0.9       -0.5
Caster           8.9        9.2
SAI              6.6        6.0
Toe              0.02       0.01

(from http://realfierotech.com/phpBB/viewtopi ... 26#p145609)

Camber seems to vary quite a bit depending on some factory tolerances, as I was only able to get -0.5 on the right. I got ~9 deg of caster on both sides though. This was without any slots, bent parts, longer ball joints, etc... just stock suspension with chopped springs for a 14" (fender to hub center) ride height.

[bse53]

Added the spacer to one side of the car tonight and I can get all the camber and caster I want. I need to make some sort of shim between the new pivot mount and frame.
One big problem, the UCA covers the lower bolts, so I may need to slot the UCA mounting points slightly so I have a small amount of adjustment.
And it eliminated the binding.




The increased caster is now mis-aligning the steering arm. I read that you can just heat the arm and bend it.

[Series8217]

Did you cut off the shock tower from your front crossmember?

[bse53]

Yes.
I'm still waiting for the Konis I ordered that are slightly taller than the present shocks, so I need to raise the mount slightly and change to the eye end. I will probably do something similar to what you did for your lower shock mounts. I'll have to work around the stock UCA, which would be less of an issue with your new UCA.

[Series8217]

Yes.
I'm still waiting for the Konis I ordered that are slightly taller than the present shocks, so I need to raise the mount slightly and change to the eye end. I will probably do something similar to what you did for your lower shock mounts. I'll have to work around the stock UCA, which would be less of an issue with your new UCA.

It looks like you will still have plenty of room. The tight spot will be the inner diameter of the upper spring perch.