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New Miata Never raced, but SAI is Wayyy off

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#1
Flyntgr

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The Hunter machine alignment machine reported my Steering Axis Inclination (SAI) of this car, which has never been raced and never wrecked, wildly off: Left side is 2.6 degrees, whereas the right side is 12.5 degrees, for a cross SAI of 9.9 degrees!!! It seems that teh factory spec of SAI is 13.7 degrees, plus or minus 1/2 degree. I had no idea the SAI was off, as a simple inspection wouldn't reveal that, and the seller agreed to align it, set the crossweights and the ride height. He might well have been in good faith, as I hope he was, but....

At this point, after trying 3 different times to get it aligned and sorted out I get the report that the SAI is apparently too far off to be driveable in racing. Q: What could be done, if anything, to get this car "right" in order to race it? Someone suggested a frame machine, but I don't know if even that would fix it? Thanks!


EPILOGUE,SEPT.17,2011:
After all the questions and dialogue, the end result as of Sept. 17th is FINE! No test results yet, but the setup is right on the money! that's all I had hoped for. AND I learned how important it is to get the car "square" as Davew says.

1. The SAI was NOT off as I had feared. What was off was the Hunter Hawkeye machine which gave a bad printout report. SAI is okay on the car. Whew! Thank God!
2. The rear camber was difficult to set, probably because the car was "new" or unsorted, but the right alignment pro who has been helping me was able to pull the A arms of the rear suspension and set them exactly at -3.0 degrees camber on each side, which was our target for the Hoosiers.
3. The seller was right about the car not being wrecked or bent, and this series of inquiries has had a happy result. However, mixed into all of this was the left rear wheel bearing that went bad and ruined the hub. New hub installed.
4. I thank everyone who posted good information and suggestions about the car. I plan to try it out next week at the track. If I don't post anything here by next Friday, you can presume "all went well."

#2
Jim Boemler

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Have you talked to the seller about it? It's at least possible that he did this intentionally. Like you, I shoot for a "balanced" setup, but some of the fast guys (and some of the wanna-be-fast guys), tweak the car for a particular track -- sometimes a particularly critical corner. Don't think ill of the seller until you know.

As for fixing, it's an alignment -- nothing special. You go for the settings you want, and if you can't get there, it's probably a matter of a bent arm. Or sub-frame, or very occasionally a bad bushing. Either way, you replace the bad part, and finish the alignment.

This is really kinda "normal" for race cars.

#3
Flyntgr

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Have you talked to the seller about it? It's at least possible that he did this intentionally. Like you, I shoot for a "balanced" setup, but some of the fast guys (and some of the wanna-be-fast guys), tweak the car for a particular track -- sometimes a particularly critical corner. Don't think ill of the seller until you know.


As for fixing, it's an alignment -- nothing special. You go for the settings you want, and if you can't get there, it's probably a matter of a bent arm. Or sub-frame, or very occasionally a bad bushing. Either way, you replace the bad part, and finish the alignment.

This is really kinda "normal" for race cars.


I have emailed the seller, but not reply yet. He may be busy or out of pocket. I'm not making any accusations, as he could well have not known of the SAI deviation.

The SAI is NOT adjustable by alignment, other than with a frame machine or some other extraordinary remedy such as subframe removal and re-positioning. The car can be partially aligned, but not with full parameters at to caster, camber and toe, but the SAI is still so far off the car doesn't steer right. But driving this car at speeds over 110 mph isn't safe, as the car drifts around and feels unstable.

Who knows what it would cost to get it straightened, if indeed it could be done accurately? Has anyone here ever had this problem? If so, what did you do to get it fixed? Thanks!

#4
davew

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What are your camber and caster numbers. That along with the sai numbers will tell you what the problem is.

Also, check your upper control arm bolts. Loosen the nut and spin the bolt. Look for movement inticating a bent bolt.

You have 4 allignment cams. If you car is an NA, measure from the outer tip of the "upside down horseshoe" on the left front to the outer tip of the horseshoe on the right front. On an NB car, there are flats built into the subframe, measure outer flat to outer flat.

A couple plumb bobs make this easier

You actually are going to take 4 measurements:
Front of the front cam
Back of the front cam
Front of the rear cam
Rear of the rear cam.

I do not remember what the measurement is, but all 4 should measure within 1/8" of the rest. If more than 1/8 difference your subframe is bent.

Give me this info and I will tell you what is bent

Dave

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#5
Flyntgr

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What are your camber and caster numbers. That along with the sai numbers will tell you what the problem is.

Also, check your upper control arm bolts. Loosen the nut and spin the bolt. Look for movement inticating a bent bolt.

You have 4 allignment cams. If you car is an NA, measure from the outer tip of the "upside down horseshoe" on the left front to the outer tip of the horseshoe on the right front. On an NB car, there are flats built into the subframe, measure outer flat to outer flat.

A couple plumb bobs make this easier

You actually are going to take 4 measurements:
Front of the front cam
Back of the front cam
Front of the rear cam
Rear of the rear cam.

I do not remember what the measurement is, but all 4 should measure within 1/8" of the rest. If more than 1/8 difference your subframe is bent.

Give me this info and I will tell you what is bent

Dave

It's a '99, NB i think. I presume the LEFT side is off more than the right: Left measures 2.6 degrees whereas the right is at 12.5 degrees. I'll see if I can get these measurements. thanks, Dave. The camber and caster numbers are:
LF Camber -2.8 degrees RF camber -2.8 degrees
Caster 4.7 4.7
Toe 0 0
Rear Camber -2.7 -2.7
toe 0.07 0.08
We couldn't get more neg. camber.

#6
Tom Hampton

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Maybe I don't understand something. But, i don't see how your sai could be off that much and still have symmetric camber unless your lf knuckle or spindle is bent.

Subframe or control arm would change camber by +10 degrees also.

Am, i missing something?

You do mean the angle of the kingpin axis in the transverse plane right?

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#7
Flyntgr

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Maybe I don't understand something. But, i don't see how your sai could be off that much and still have symmetric camber unless your lf knuckle or spindle is bent.

Subframe or control arm would change camber by +10 degrees also.

Am, i missing something?

You do mean the angle of the kingpin axis in the transverse plane right?


Tom, the camber isn't 10 degrees off, it's the Steering Axis Inclination (SAI), aka Kingpin Inclination which is off, more on the left than on the right-but both are off if 13.7 degrees is spec.

I suspect the subframe is not right-probably not bent, but attached wrong in some way. Perhaps removal of the front subframe and use of shims would take car of it, perhaps not. The alignment machine detected and reported the variance in SAI. I don't know nearly enough to know what to do to correct it, but from what the seller told me I have to presume that the suspension parts are NOT bent. I'll take it to a frame expert and let him figure it out. I'm hoping it CAN be fixed, but don't know for sure. Thanks for your posts.

#8
Tom Hampton

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Right. My point is that if the sub or control arms were bent enough to affect sai then your camber would have to be off the same amount.

Sai and camber are in the same plane and are caused by the same suspension change.... axis of upper and lower ball joints.

So, in order for sai to change without a corresponding change in camber, the plane of wheel rotation must move relative to the kingpin plane. In other words, the knuckle is bent.

In addition, since your camber has not been affected, your lca or pickup points should be bent and are compensating for the knuckle.

Looking at my knuckle, the weakest point appears to be the upper ball joint arm. 10 degrees is a lot, if it really that bent you should be able to see it.

The point in specifying sai and checking it is to detect bent spindles and knuckles. It is not independently adjustable separate from camber.

I would take off your front brakes on both sides and carefully measure the angles between the kingpin and the spindle on both sides. On should be way different from the other.

-tch
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#9
Tom Hampton

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Oh... one more thing.... ignore the seller's remark. never presume anything. You'll just be mad at yourself later when you find out your presumption was wrong and you spent 2 days going down the wrong track.

-tch
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#10
davew

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I think you are getting WAYYYY ahead of yourself.

In my former life (pre Spec Miata) I was an allignment tech and specialised in suspension wrecks from every body shop in town. It is geometericly imposible for SAI to be that far off and have normal camber/caster readings. Camber and caster is derived from SAI. Therefore I believe you have operator/machine error on the allignment check.

Before getting all crazy about this, you need to understand the Miata suspension design. You could literally take the entire front suspension off the car and mount it under a set of saw horses, and create the same readings. The entiree suspension bolts to the subframe. No shims required. Taking the car to a frame machine will do you no good.

SAI is a diagnostic measurement. There is no reason to measure it UNLESS camber and caster are off.

From the info you posted, I do not think anything is wrong with your car.

Dave

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#11
Tom Hampton

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I think you are getting WAYYYY ahead of yourself.

In my former life (pre Spec Miata) I was an allignment tech and specialised in suspension wrecks from every body shop in town. It is geometericly imposible for SAI to be that far off and have normal camber/caster readings. Camber and caster is derived from SAI. Therefore I believe you have operator/machine error on the allignment check.

Before getting all crazy about this, you need to understand the Miata suspension design. You could literally take the entire front suspension off the car and mount it under a set of saw horses, and create the same readings. The entiree suspension bolts to the subframe. No shims required. Taking the car to a frame machine will do you no good.

SAI is a diagnostic measurement. There is no reason to measure it UNLESS camber and caster are off.

From the info you posted, I do not think anything is wrong with your car.

Dave


Not that it adds any credence to what you say (you know way more than me), but I agree with you, in that I think the measurement itself is suspect.

Just so I can validate my own thoughts, though....you say "impossible", but my understanding is this:

1. given the size of the knuckle, this change (if it were real) would mean that the lower ball joint has been moved towards the centerline by approximately 1". This could be caused by either a bent LCA, or a bent subframe (displaced pickup points).

2. This displacement would cause a simultaneous change in SAI and camber, of the same magnitude and sign (+10 degrees). That would make camber arount +7 degrees.

3. Given that camber is still negative 3 degrees (in round numbers), one of two things would have to be true:
3a. The steel arm of the knuckle leading to the upper ball joint would have to be bent inwards towards the centerline proportionately to return the spindle to the normal orientation (to allow negative 3 degrees of camber).
3b. The spindle would have to be bent where it joins to the knuckle.

So, it seems like it is POSSIBLE, for these measurements to be real. In other words, there is a way to physically bend the parts to arrive at the measurements. Again, unless I'm missing something...and, I very well could be (that's my real point in this follow-up....to clarify my understanding).

The crux then (for me) is the liklihood of an impact that precisly bent the kingpin and the LCA/subframe in such a way as to exactly offset each deformity. Further, the odds of the kingpin bending ONLY in the transverse plane (affecting SAI), and not bending in the longitudinal plane (affecting caster) seems hard to even fathom. Finally, such an impact should have also bent the tie-rod. So, there should be eveidence of a new tie-rod/ends/steering rack...even if its been repaired.

Alternatively, the spindle could be bent, but it seems even less likely that it wouldn't make some horrible noise/wobble/ or the hub barely turn.

Assuming Dave acknowleges the (highly unlikely, but POSSIBLE) analysis above:

To separate truth from fiction, you still should LOOK at the knuckle and see evidence of this much bending. Given the amount of movement required (roughly 1 inch at the lower ball joint) it should be pretty easy to SEE. The lower ball joint MUST be approximately one inch closer to the subframe on the bad side. Further, you are looking for 1/2 to 3/4 of an inch of bending in the upper arm of the knuckle.

If this bending isn't there, then someone made a mistake somewhere. The lower ball joint has to have moved inwards by at least an inch, in order for any of this to hold water.

Also, look at the tie-rod adjustment. If the lower-ball joint has moved this much, that side should be nearly fully retracted in order to compensate.

-tch
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#12
Jim Boemler

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Tom, what you're missing is that while SAI could be way out and camber somehow adjusted to compensate, the caster measurement would still be out in left field. If camber AND caster are OK, then SAI has to also be OK. Thanks Dave, for the clear description.

#13
Tom Hampton

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Tom, what you're missing is that while SAI could be way out and camber somehow adjusted to compensate, the caster measurement would still be out in left field. If camber AND caster are OK, then SAI has to also be OK. Thanks Dave, for the clear description.


Thanks, Jim...but, I'm not convinced, yet. I suppose I don't have to be convinced...but, if I'm wrong I'd like to understand where I got off.

Caster and SAI are orthogonal measurements of the line passing through the upper and lower ball joints (projection of the kingpin onto their respective planes): SAI in the vertical plane perpendicular to the direction of travel, and Caster in the veritcal plane parallel to the direction of travel. If SAI were the vector sum of caster and camber I would understand why you say that.

Once you remove the constraints of fixed distances between points in space by bending metal, I don't think its impossible.

I'm not talking about making adjustments through the cam bolts, I'm talking about adjustments through bent metal. I understand what you're saying if we are talking about using the cam bolts to adjust because the cam bolts aren't truely orthogonal adjustments. But, the cam bolts can't correct for 10 degrees of misalignment, anyway.

-tch
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#14
Jim Boemler

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I agree about the lack of 10 degrees of adjustment, which is part of why Dave is suspicious of the measurement.

#15
Tom Hampton

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I agree about the lack of 10 degrees of adjustment, which is part of why Dave is suspicious of the measurement.


Oh sure. Agree with my last 12 words...and leave me hanging on the other 2 paragraphs!

Sorry, I can be a "little" argumentative sometimes.B)

-tch
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#16
Jim Boemler

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Sorry Tom. I'm in a lot of pain right now, and just trying to spread it around. ;) Mostly hoping Dave will chime in with a crisp explanation.

#17
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Put a 1/16 total toe out in the front & take it to a track. Let the car talk to you.
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#18
Flyntgr

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Put a 1/16 total toe out in the front & take it to a track. Let the casr talk to you.

Persistence has validated your questions and concerns. I have driven several hundred miles to 4 different shops and 5 different machines, including a frame machine, to two alignment experts and one frame expert, and have a report to make. The last expert, both a machinist and alignment technician of some renown, was able to check the car on his TWO Hunter machines and confirm the findings of the frame expert: there was only ONE degree of actual variance in the SAI. The Hunter Hawkeye machine which had reported 9.9 degrees variance was in error! And by machining the right rear cam he was able to symetrically align the car with the amount of camber and toe that I had wanted in the rear. Whew! hundreds of miles and hundreds of bucks later, I can finally breathe easier in the knowledge that the car is probably okay with the last alignment.
I will indeed take the car to the track and try it out-this Thursday.

I am very pleased that the car is not unsalvagable or unusable. I was sure the seller was in the utmost good faith, but was perplexed that the car could be so far off-which is turned out NOT to be. The cam modification gave it just enough adjustment to utilize the amount of adjusting space that was available but not usable without the cam being reduced on one side and increased on the other. He took material off one side, and welded additionaly material to the other side. As a machinist who makes parts from scratch he had the knowledge and expertise to do this with his own equipment. Don't ask me more details on this, as this is far, far above my pay grade to understand.

In short, there was a problem in the rear, but it has apparently been fixed. The problem of SAI variance in the front was not nearly as much as the Hunter machine had reported (possibly a glitch in the machine exacerbated by the large negative camber angles put into this race car, which are much above the normal camber used in street cars).

Thanks to all of you who responded. I am certainly pleased that this saga may close with a happy ending! I'll find out more on Thursday at the track! Zoom-Zoom-Zoom.

#19
Tom Hampton

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That modification is illegal in sm.

-tch
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#20
Tom Hampton

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Hundreds of dollars? Seriously? Holy crap! When all you had to do was take a couple measurements and visually inspect the parts? And now you have an illegal race car?

Sorry, but that seems a bit foolish.

Why did you ask us, if you weren't going to listen?

-tch
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