Rear Alignment: Relationship between Camber and Toe, Talking through my settings, interested in informed feedback! |
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Rear Alignment: Relationship between Camber and Toe, Talking through my settings, interested in informed feedback! |
Morrie |
Aug 13 2022, 01:46 PM
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#1
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Member Group: Members Posts: 181 Joined: 8-October 07 From: Cedar Park, Texas Member No.: 8,198 Region Association: Southwest Region |
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' Rear Right: Camber: -1 deg 12' 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 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 Rear: New 100lb Eibach coils Thanks Guys! |
Superhawk996 |
Aug 13 2022, 02:05 PM
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#2
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914 Guru Group: Members Posts: 6,469 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch |
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 |
Aug 13 2022, 03:56 PM
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#3
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Senior Member Group: Members Posts: 928 Joined: 3-October 06 From: Ossining, NY Member No.: 6,985 Region Association: None |
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
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Superhawk996 |
Aug 13 2022, 04:46 PM
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#4
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914 Guru Group: Members Posts: 6,469 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch |
. . . 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 |
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