Rear Alignment: Relationship between Camber and Toe, Talking through my settings, interested in informed feedback! Options

[Morrie]

Hi Guys!

I had my car 4 wheel aligned yesterday and overall went well. I've replaced all the bushings, shocks, struts, springs, bearings, etc so it was all totally out of wack....

Good news, everything came into spec in front. All good. Car drives great now. In the rear I needed a bit of camber to clear the tops of my tires, so I am sitting here:

Rear Left:

Camber: -1 deg 24'
Toe: -0 deg 18'

Rear Right:

Camber: -1 deg 12'
Toe: -0 deg 02'

Camber: Factory says max difference from left to right is +/- 20'. I've got 12' difference side to side so I think I am okay there, even though the extra camber may cause some tire wear that I can live with.

Toe: Factory says toe should be 0deg +15' per side. The alignment shop set limits to 0deg +/- 15'.

A lot of numbers and I can make a bunch of guesses, but I would like to know for my road car which gets some spirited hill country driving, should I work on getting more positive rear camber toe, and is it as opening up the slots in the outside suspension arm mounts to allow for more rear travel of the arm?

Sorry if this is beaten to death or overcomplicated. Writing it down here helped me get it straight in my head. (IMG:style_emoticons/default/blink.gif) If it helps, below are my suspension settings and condition. Car was corner balanced prior to going for alignment, and is slightly lowered. Clearance on the RH side (passengers) rear tire is tight but it does clear with the current settings.

Front:

Stock Torsion Bars
15mm stock front anti sway bar with new bushings
Turbo Tie Rods
New Ball Joints
New 914 Rubber bushings
New front Koni Red externally adjustable strut inserts.
New Wheel Bearings
16x6 5 lug Fuchs
Bridgestone Potenza RE980 A/S Plus, 205 /55 R16

Rear:

New 100lb Eibach coils
Ground Control adjustable spring perches
Koni Red adjustable shock absorbers
New 914 Rubber bushings
New rear wheel bearings
16x6 5 lug Fuchs
Bridgestone Potenza RE980 A/S Plus, 205 /55 R16

Thanks Guys!

[Superhawk996]

A lot of numbers and I can make a bunch of guesses, but I would like to know for my road car which gets some spirited hill country driving, should I work on getting more positive rear camber, and is it as opening up the slots in the outside suspension arm mounts to allow for more rear travel of the arm?

I think you wrote it down wrong?

You would want more NEGATIVE camber if anything to improve handling. Camber is controlled by shims under the outboard rear suspension point, not the longitudinal (fore/aft) position of the arm mounts. That statement leads me to believe you're trying to get more toe?

Likewise, I'd look at getting the toe corrected to be symmetric and to have toe in. You don't want to be approaching zero toe when lateral loading is trying to push you toward rear toe out on the 914 Semi Trailing arm setup.



You do not want rear toe out under any circumstance for street use.

You have spec correct: Toe: Factory says toe should be 0deg +15' per side. This means you have no toe (0 degrees - worst case) or 15' of TOE IN (what you want).

So, take the car back and have them make the rear TOE IN and make it symmetric assuming you have the sign conventions written down correctly.

In order to create toe in -- the outboard rear suspension mounts will be pushed forward -- there is no need to slot anything to achieve the OEM alignment.

I'll repeat myself - DO NOT slot anything.

Actually, as I think about this a bit more -- I might very well just avoid that alignment shop. Any shop that set rear toe out is probably incompetent assuming your sign conventions are written down correctly.

[Morrie]

I think you wrote it down wrong?

You would want more NEGATIVE camber if anything to improve handling. Camber is controlled by shims under the outboard rear suspension point, not the longitudinal (fore/aft) position of the arm mounts. That statement leads me to believe you're trying to get more toe?

I wrote "camber" where I meant to say "toe". I have corrected my original post. I am trying to get more toe. Thanks for pointing out the error. It will not be my last.

Likewise, I'd look at getting the toe corrected to be symmetric and to have toe in. You don't want to be approaching zero toe when lateral loading is trying to push you toward rear toe out on the 914 Semi Trailing arm setup.

You do not want rear toe out under any circumstance for street use.

You have spec correct: Toe: Factory says toe should be 0deg +15' per side. This means you have no toe (0 degrees - worst case) or 15' of TOE IN (what you want).

So, take the car back and have them make the rear TOE IN and make it symmetric assuming you have the sign conventions written down correctly.

In order to create toe in -- the outboard rear suspension mounts will be pushed forward -- there is no need to slot anything to achieve the OEM alignment.

The specs the shop had loaded in their computer are centered on zero rear toe, +/-15'. Porsche manual shows 0deg, +15' / -0'. Tech said this was best he could get with the current condition of the chassis.

I am working with what I have here, a 50 year old car that has issues. The reason why I commented about increasing the "reach" of the holes in the outboard suspension mounts was to attempt to compensate for the current alignment of the chassis, as it is. Chassis took a hard hit a couple years ago (thankfully I am okay) and I am sure it did not do it any favors. It is solid, but most likely not "perfectly" straight, and sadly I am not in a position to do anything more heroic with it than what I have. I was actually pleased it was as close as it is.....

Thank you, for the patience, explanations, and comments. It is very much appreciated.

[Superhawk996]

The specs the shop had loaded in their computer are centered on zero rear toe, +/-15'. Porsche manual shows 0deg, +15' / -0'.

Shop specs are wrong.

What worries me more is any shop that would send a customer out the door with with rear toe out. They should know better. That shop is one accident, and one good lawyer away from having their butts sued and the customer owning an alignment shop. In your case, if the vehicle has been damaged and the car can't be adjusted to toe in - that is a different situation. Regardless, their shop specs are wrong.

I'm not going to claim I know the alignment specs for all production vehicles ever produced but honestly, I'm not aware of a single production vehicle that has rear toe out as part of their production alignment specification.

So back to your situation. Before slotting the outer suspension attachment -- find out why you can't achieve toe in. Fix that.

As ChrisFoley suggested, if you have a bent trailing arm, that needs to be fixed. Likewise, make sure your body side outer suspension consoles aren't rusted or deformed from an accident. Don't be driving around and doing spirited driving on damaged parts. The last thing you need is have a damaged / cracked part fail catastrophically mid-corner. There are plenty of spare parts available at reasonable pricing on the FS/WTB forum. Post an add if you need parts.