George A

Bob, I think you got that backwards. It's -2.5degrees of camber and 8 degrees of caster. If not, your car must look pretty funny.

George

Bob Rouleau

ROTFL Bob D, your car much have wicked turn-in! Better not take your hands off the wheel though..

macfly

ldw, thanks so much for such a comprehensive and clear answer. I do have a tire rubbing, but only on absolute full lock, and it seems to be on the brake cooling duct, not the inner wheel well area.

My next mission will be to find a laser sighted, hi tech, Pcar specialist alignment shop in the LA area. Since Johnson's who did the original work do everything the old fashioned way I won't bother going back there.
Anyone got any ideas?

Jack

Andrew: Contact Tom Chan at Lucent Motors 310-231-3328 -- he's got the latest Hunter laser alignment equipment and knows how to use it on Porsches. He's also very careful/**** about customers' cars -- you'll like him and his shop. If you need more info, call me.

Viken

Andrew, call Tom Chan at Lucent Motors and ask him to have an alignment job of a laser rack. He is as **** as they come with his work. I think you need to reverse the procedure and go back to shims for increased negative camber. Tell Tom I said hi.

Jack

Viken -- you were a little late with your post -- by at least 30 seconds. LOL

mds

Thanks, lynn, your comments are helpful. Here are some notes on my car updated with your insights in mind:

My first attempt with a track alignment was at -2.5 camber with the strut tops in the standard position and arms in the standard hole. 8mm of shims per side were required and the caster did increase slightly. On one laser machine it was 8.9 on a second 8.2. I had the alignment done twice at these settings, I don't know why the two machines differed in caster measurement. In any case, it does appear that shimming causes caster to increase slightly.

I then wanted to try -3.0 camber and tried adding shims, but the bolts did not have enough threads, so I rotated the strut tops and removed shims down to 3mm per side, with the arms still in the standard hole. Doing so left the sliding adjustment at the top of the structs roughly in the middle position. Caster now was 8.0 on the laser that had read 8.2 in the above paragraph.

-3.0 camber turned out to be too much with MPSCs, so I wanted to go back to -2.5. The only way to do this with rotated tops was to remove all shims. Of course I could have gone back to the original setup with untwisted tops and lots of shims, but it was less labor to leave the strut tops twisted and simply remove the shims. Doing so the end result was -2.6 camber and 7.8 caster, again on the machine that read 8.2 initially. I could not get my target of -2.5, the minimum was -2.6, but I felt that was close enough.

So my conclusion is as follows. To get -2.5 camber on my car, you can shim and end up with slightly over-spec caster, or you can rotate the strut tops and end up with slightly under-spec caster. Because the laser machines differ, it is hard to tell just how over or under spec you are. Also these two setups probably differ dynamically in some respects, but I have not felt any difference. Of course, I am new to the car and probably have not learned to feel such differences.

bob_dallas

I was wondering why the inside of my tires were wearing about a 1/2" wide patch...

I was a little tired and in a hurry when I typed that I suppose...

ldw

hmmmm,... Interesting. So this would suggest that the rotation of the strut may not really affect caster in the way that I thought based on the measurement of 9.0 that macfly obtained. The "old fashioned way" works just fine and some shops and alignment people continue to use this method without the technology of laser type alignment units. In fact, at the track, one must use string.

So, i suspect if macfly gets the alignment checked, it will be less than 9.0 and likely close to spec if not within spec. Anything between 7.5 and 8.5 degrees is considered specification. Keep in mind, some machines are calibrated for degrees and minutes. In that case, the measurement would obviously read 7 30' and 8 30'.

Mike, the caster measurement is very sensitive to calibration AND how the wheels are oriented during the procedure. The wheels themselves must be taken through a sweep and then into a neutral range before this measurement is "locked" in by the computer unit. If calibration is off, or your ride height changed a bit between meaurements, you could see changes in caster as you have described. It is also important to roll the car back and forth and rock it up and down a few times to allow the springs and other suspension parts to 'settle' prior to concluding final measurements.

buckdr1

Interesting thread, but sounds like you can get yourself in some deep do do. I'll track mine stock for now! I'm sure I'll be smiling.
Lynn, nice to hear from a local, I'm over in Newtown.
Bill