Question about WRX SAI alignment angle

[Bob Lund]

I had my MY03 WRX wagon aligned and the SAI secondary angle was measured
at 10.25/8.83 (left/right). The spec for SAI is 13.83 - 15.33. The
alignment guy said this is not adjustable but could be indicative of
mechanical damage. His advice was it was no problem and to ignore it. I
called one local Subaru dealer and the service manager didn't know what
SAI was. I called another dealer and the service guy (who at least knew
what I was talking about) also said don't worry about it.

I should add that all other alignment angles are in spec after the
alignment.

Does anyone who knows more about alignment and WRXs than I do have a
thought about whether SAI out of spec is something to be concerned about?

Thanks in advance,
Bob

 

[Blair Baucom]

From http://autorepair.about.com/cs/generalinfo/a/aa012201a_2.htm



Steering Axis Inclination (SAI):
The angle formed by a line that runs through the upper and lower steering
pivots with respect to vertical. On a SLA suspension, the line runs through
the upper and lower ball joints. On a MacPherson strut suspension, the line
runs through the lower ball joint and upper strut mount or bearing plate.
Viewed from the front, SAI is also the inward tilt of the steering axis.
Like caster, it provides directional stability. But it also reduces steering
effort by reducing the scrub radius. SAI is a built-in nonadjustable angle
and is used with camber and the included angle to diagnose bent spindles,
struts and mislocated crossmembers.



Like he said, not much you can do, unless it is a damaged strut, assuming
the MY03 has struts. Unless the edges of the tires are showing excessive
wear, I would not worry.



Blair

 

[Bob Lund]

Thanks for the reply.

The reason I got the car aligned was from excessive wear on the inner
shoulders of the tires. Both the toe-in and SAI were out of spec. The
alignment adjusted the toe-in.

I believe the MY03 WRX has struts so I am left with the uncertainty of
whether the out of spec toe-in was responsible for the unusual tire wear
or if there is strut damage (as evidenced by the out of spec SAI).

Either replacing the struts or going through another set of tires is
going to be an expensive way to find out. I was hoping to find some
information that would help me figure out if a: strut damage is likely
given the SAI measurement and b: if there is damage is it enough that it
will affect tire are. I don't know if the struts can be looked at to
determine their health; I'm guessing not.

Bob

 

[Blair Baucom]

Not sure if a strut can be rotated 180 degrees and then rechecked. If it is
bent, this should shift the SAI. The other thing would be to swap left for
right. The other option is a body shop which could check the car for
alignment issues using a laser that is normally done for unibody repairs
after an accident.

I know this decision is tricky as the checks may exceed tire costs due to
excessive wear.

Blair

 

[Bob Noble]

The toe-in out of spec could cause the kind of wear damage you describe.
That's what toe-in out of spec does.
So now just wait and watch and you'll have your answer. If you start to
notice uneven wear, do something about it before it gets too bad and it
won't be a problem.

 

[StephenW]

These guys are dead on correct with the information. I have had training in
SAI and I still have difficulties with it. Bottom line, if Camber, Caster
and Toe are within spec; don't sweat SAI.
As far ar struts go, mostly sub's bend at the bottom and cause a camber
problem, sometimes the control arms bend too, all will throw the
camber/caster out.

Dive it; if it dosn't pull/drift or wear tires you don't have a problem.

Steve
ASE Master tech.