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!

[Montreal914]

Looking forward to reading input from the “pros” (IMG:style_emoticons/default/smile.gif)

You don’t have sway bars?

[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.

[stownsen914]

Have to agree on the toe in at the rear. Definitely no toe out. And more even on each side. I'd go with the high side of the spec for toe in too, 914s are known to flex in the rear under corner forces, which will tend to flex toward toe in i meant toe out, duh. Better to have some buffer.

[Superhawk996]

. . . 914s are known to flex in the rear under corner forces, which will tend to flex toward toe in.

Semi Trailing Arms tend to flex (physical deformation of the arm & also due to pivot bushing deflections) toward Toe out under high lateral load. Is there something unique to the 914 that I'm missing?

Or - are you referring to the fact that the semi trailing arm is designed to toe in as it moves upward toward jounce? Similarly, as the vehicle body rolls, that effectively puts the outside suspension into jounce (and more toe in - excluding lateral forces).

Semi Trailing arms geometry is set up this way; increases rear toe in under jounce / roll to help counteract the tendency of the semi trailing arm to toe out under lateral loads and deflections of the arm itself.


I apologize, I suspect I'm on a bit of a tangent related to suspension design. At cornering forces being encountered during spirited road driving (let's say less than ~0.5G) I would agree completely that it is correct to say that toe in is indeed increasing as the body rolls. This is done by design.

For those interested, the Weissuch semi trailing arm design used on the 928 performs differently than the traditional semi trailing arm setup on the 914. Don't confuse 928 behavior for traditional semi trailing arm behavior. Porsche did some really good stuff with the 928 rear suspension that was ground breaking at the time.

Here is a clarification.


Going even further down the rabbit hole, here is a great link to a member's post that measured the 914 toe curves as the rear semi trailing arm moves though it's range of motion.
http://www.914world.com/bbs2/index.php?sho...=41325&st=0

[sixnotfour]

Good Ole Ray Scruggs..
https://silo.tips/download/home-alignment-o...step-by-step-gu

[Morrie]

You don’t have sway bars?

First of many edits to my original post. Good catch, I have a 15mm stock front bar. Good catch and thanks for being patient with me!!

[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.

[ChrisFoley]

On the side that you can't get toe in, the trailing arm may be bent.

[mlindner]

I had the same issue in the rear...little toe out after doing a string alignment.
To fix, I long-gaitted the holes in the control arm brackets. worked well, now just a little toe in, nice. Mark

[Morrie]

On the side that you can't get toe in, the trailing arm may be bent.

That wouldn’t surprise me Chris.

[Morrie]

I had the same issue in the rear...little toe out after doing a string alignment.
To fix, I long-gaitted the holes in the control arm brackets. worked well, now just a little toe in, nice. Mark

That is probably where I am heading, Mark. May be the easiest path to getting things in spec. How much did you have to remove to move how far? I am trying to get an approximate idea before I go after it.

[mlindner]

Morrie, just 1/16 or so on the trailing edge of the three holes, then the bracket could move a little forward creating toe-in. Both right and left side were off (positive) in the same amount, so not sure if they were bent. Butt I did weld the stiffining kit to the control arms so that could have been the cause. Best, Mark

[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.

[mlindner]

I agree 100% with Superhawk996, you need to find the problem and have it fixed. Just FYI, my car was a complete rebuild, cleaned and spec'ed or replaced parts. Thats why I felt comfortable with the long-gated holes in order to achieve toe in. And thanks Chris for your comment regarding stiffening kit....that explain that. Mark

[ChrisFoley]

Butt I did weld the stiffining kit to the control arms so that could have been the cause. Best, Mark

Installing the 3 sided overlay reinforcements always causes warpage that leads to toe out.

[914_teener]

Butt I did weld the stiffining kit to the control arms so that could have been the cause. Best, Mark

Installing the 3 sided overlay reinforcements always causes warpage that leads to toe out.

I didn't read that you replaced the rear bushings on the trailing arms. Did you?

I'd echo what Chris says. When I did mine I checked them on a surface plate before I reinstalled them. Didn't want to take the whole mess apart twice...particulary the CV's to find out I couldn't align the rear.

AND...there are a bunch of threads on how to strenghthen them and when you would want to. I

[dr914@autoatlanta.com]

the rear camber HAS to be 30 minutes or the inside of the tires will wear. You can accomplish by adding a 20 and a 40 shim on the left and a 40 shim on the right rear

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!

[Morrie]

Shop specs are wrong.

Agreed. They were set around a zero value with a tolerance. If they had to tolerance this, the zero point should have been one of the limits, and 15' the other.

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.

To put this one to bed for good, when I picked up the car, the alignment tech came out and discussed this with me specifically as a concern, that he could not zero the numbers. He mentioned that the values were on the wrong end of the target and was concerned about both that and the fact the limits were not identical. This was not lost on him, and not glossed over. He made it clear that this needed to be fixed, and the car brought back in to finish the alignment verification.

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.

Good news here is that this is a very solid car regarding rust. The mounts are clean and free of corrosion on the inboard side, hell hole is clean and not compromised also. There is no visual evidence of damage. This is not an indication or suggestion that damage is not present in a way that is not visible, and I understand that careful measurements are required to determine proper alignment of suspension relate components. More to come.

[Morrie]

the rear camber HAS to be 30 minutes or the inside of the tires will wear. You can accomplish by adding a 20 and a 40 shim on the left and a 40 shim on the right rear

Thanks George, I would like to get this set also. I have the shims, and the drivers side has good clearance to accomplish this. Problem is the passengers side is very tight clearance at the moment, chassis is offset that direction. I am clearing with the current settings but likely would rub on the outside edge if I came to 30' of negative camber. Short term I plan to get left and right the same, and take it from there. The whole situation may end up resulting in replacement of the trailing arms. Luckily the rear o fthe car comes apart easily.