Larry Velk

Putting a number to Dr Bob's remark - if you take a generic 65 inches as a track width a 10.0 mm height variance is 0.35 degrees or about 20 seconds of arc. In a way, it demonstates that camber isn't that big a deal as a fat (no PC talk from me) driver could do a few mm's of damage to the old ride height. In actual practice moving the height 10.0 mm doesn't have this great an effect due to compliance in the system, but it does, in theory.

Earl Gillstrom

Gassman, and others interested in 928 wheel alignment.
PLEASE read all of my wheel alignment tutorial, ALL sections.
ALL sections. If it is not complete, please tell me what is missing.
The location is in my signature.

Earl

largecar379

things I did AFTER my s4 suspension upgrade:

tightened the lower suspension arm attaching bolts after returning the car to the ground. (this allows for most of the "settling" that every one howls about)

made sure that the spring/shock adjustment was equal side to side.

made sure tire pressures were exactly the same-side to side.

put fuel tank level at 3/4 full.

found a brand spankin' new Hunter alignment rack (computerized laser unit with the neat reflective panels) being installed at my local tire shop, had a long conversation with the alignment tech and Hunter rep prior alignment.

drove car about 50 miles prior to alignment (most folks advocate 100 miles after any jacking, but remember, I did not tighten the lower arms until the car was on the ground and settled).

put 150 pounds of weight in the driver's seat.

aligned car according to factory specs.

Car has over 500 miles since and tire wear is, well, there is no noticeable tire wear.....

dr bob

This can get confusing fast. A 10mm difference in floor elevation side to side will resut in that camber difference. If the car is sagging 10mm on one side though, the camber change may or may not be significant. It depends on where the control arms are in their arc, a factor of static ride height. With the car at factory spec height or close to it, the sagging will only very slightly affect camber. A car that's sagging a lot wil have a slightly bigger error. No matter what, the change in ride height won't cost the 0.35 degrees though.


As Earl reminds us, we need to read and understand his sections on alignment before we draw conclusions.

Larry Velk

Yes on the diff between floor out of level and ride height. Floor diff would cause the error I suggested, as Dr. Bob says, ride height won't necc. cause this error. On our cars if you jacked one side in the front 10. mm while the car just sat there without bouncing the car around I doubt the other side camber would move enough to notice.
My IRS daily drivers have 'non - adjustible' camber front and rear. The springs sag (and break) and we run considerable negative camber on them (-1.5 in rear, minimum). Tire wear is not that severe, considering. Get the toe wrong and the edges would burn off in nothing flat.
I bet most 928's (certainly ours) run a bit too much rear camber. If its 0.5 degree too much I don't think it is a huge deal - but it also isn't I-deal.
I used all the Earl info and made the wheel pads, have 2 normed-out lasers, a nice shop, and know my trig pretty well, and our car is "close" on all the cambers and right on on the toes. It drives fine and the Michelin snows show no wear. The info on getting the center line correct are very key. If you follow his steps you won't get a dog-track, which is possible with some home grown systems. Significant digits, for those of you who remember chemistry, is a huge deal. Many ace mechanics don't get this and over estimate how accurate they are or need to be. The bloom on the stinkin' laser dot alone is a source of possible error. Years ago I saw Danny Ongais' mechanics arguing at Elkhart Lake about which way to scew stuff to change his camber - he still ran OK, they were using string. If our rims weren't as good as they are we couldn't hardly even do this stuff in our home shops as the run out on old 50's steel wheels is so bad.

dr bob

The 'bloom' in the lasers is no small concern. I sorted through several to find a pair with least of that bunch. Then found another set of different heritage that had a whole lot less. During the 'calibration' process on my laser fixtures, an executive decision was made to just use the center of the 'bloomed' pattern for the near and far readings. That proved to be a good decision, as there is virtually no cross-reflection making the bloom, at least within the 10 ft or so max measuring distances I've used so far for actual toe checks.

Getting the wheels aligned parallel to the center of the car is very important and not at all difficult. Earl Gillstrom gave me some good help on that in his instructions, particularly where he shows the lasres rotated toward the rear to get the space from wheel centers equal on both sides. Do the same from the rear wheels looking forward, and the car will track perfectly.

Rge excessive rear camber issue is tied to sagging rear springs, and also to upper bushings that have collapsed a little. Got wide rear wheels and/or spacers moving the tire out? Puts more pressure on those upper bushings. This is a spot where an adjustable-length arm would be a handy improvement.