Rear end instability

[suj]

Don't bash me for asking, but what's the purpose of adding shims if rear wheels have fixed alignment? Wouldn't that add more issues than it would solve? Correct me if I'm wrong, but if wheels cannot be aligned, then it means that rear wheels can't be out of alignment.

Anyway, I scheduled wheel alignment check this Monday. I'll let you guys know how it went.

Most things have been answered but I will expand.

So the rear axle is "fixed" in the sense you have no adjustment as it is, you cannot put "camber" adjustment on the top mounts or bottom, also if you did "move the rear frame" it could give you more negative toe let's say on the left wheel, the right wheel will get the opposite (positive toe).

It was designed around standard suspension, so as you lower it, it naturally cambers and toes (if you put load on a rear wheel, you'll see it in smaller effects).
The shim is an individual shim per side, where the stub axle meets the rear axle, as this is where the wheel then mounts to, this is what you are putting whatever combination of camber and toe shim to get your desired number. Then you do the the same process on the other side.
In an ideal world you would use the same shims left and right, but in reality it won't be the case (due to many factors, not lowered equally, warped axles, etc).

If what you said was correct, then you wouldn't ever have a need to have toe adjustment on the front or people wouldn't need camber adjustment.
Also it isn't just for track cars, people use shims on OEM cars due to what I explained about about wearing of components.

 

[dsitum]

Guys, just to give you an update.
Someone here mentioned that you should visit high quality garage - the staff who know what they are doing during wheel alignment process.

Due to that reason alone, I had to visit the same workshop twice. The guy who worked on my car first time didn't print out the results. Because my father in law is a mechanic and he knew some people there, he ordered a printout.
It turned out that some measurements were in red. Now the question is did they do wheel alignment at all (first photo) the first time.

After having a discussion with them, they did another wheel alignment for free, with printouts delivered.

Lesson learned! Always ask for the paper telling you about the results of wheel alignment, because you'll never know whether they did the alignment or not.

Here are the results after first alignment:


You can see that "before" measurements are missing.

And here are measurements after 2nd alignment:



In this photographs you can also find marginal values, which I'm going to list below with a legend.

Legend and marginal values:

"Prije" mjere => Measurements "before"
"Sada" mjere => Measurements "now"
Lijevi prednji => Front left
Desni prednji => Front right
Lijevi zadnji => Rear left
Desni zadnji => Rear right
Nagib => Camber (F: -0°29' .. -1°29' ; R: -1°13' .. -1°53')
Zatur => Caster (F: 6°17' .. 4°59')
Trag => Toe (F: -1.9mm .. -0.2mm ; R: 0.1mm .. 6.5mm)
Ukupni trag => Total toe

According to the manufacturer specs, camber and caster are not adjustable on front wheels, and camber and toe are not adjustable on the rear wheels.

There are various sites which can help you convert toe from millimeters to degrees and vice versa, depending on what you need.

I don't plan to touch anything in the rear (with shims, as some guys mentioned), as everything was in green. I'm going to leave that to some better times

Finally, after the alignment, the car feels somewhat more stable. I don't know if it's placebo or not, but it definitely feels safer to me in the corners.