dwe8922

I've had a problem with the right front tire chewing up the innner half much faster than on the left side. I have a friend who is a porsche master tech who has been helping me with my car since I've been in school, and we can't seem to figure out what's causing this. We aligned the car to the specs below 4/22/04, and I did 3 track events. We checked the alignment a year later, and made some adjustments, ran 3 track events since, and am having the same problem. Here are the most pertinent facts I can think of:
-using mpsc's track, bridgestone so2's street, same wear pattern on both
-swap fronts right to left each day for track days; same accelerated wear on right front
-51k miles, no accidents
-front strut brace, pss9's, camber plates, rs sways

-4/22/04 alignment (in degrees)
front: camber L-2.3 R-2.4
caster L4.4 R4.7
toe .04
cross camber 0.1
cross caster -.2
total toe .08
REAR
camber -1.8
toe -.02
cross camber .1
total toe -.01
thrust angle -.01

4/8/05 alignment changes
front camber -2.0
rear camber -2.0
toe front 0.0

-We were concerned of the thrust angle, which checked out ok, and we removed the toe out, but this didn't seem to have an effect
-We noticed the rear bushings were worn, and only allowed a minimum of -2.0 deg camber (wanted to get to -1.5).
-the only other peculiarity to the car, is that the rear fenders have an overhang difference of 1/4-3/8" from right to left, which had me wonder if it might have a tweaked tub, but from talking to several mechanics, I've come to find that that is common in the 993 and earlier cars.

Also, does anyone know of a source of bushings without having to buy the suspension arms along with?

Thanks in advance, and any advice would be appreciated!
David

RedlineMan

Hey;

The biggest enemy of inner wear is excessive toe-out. Your numbers look fine. The second biggest - for the right front - is excessive body roll causing drag wear. Usually lessening negative camber works (differential settings). Your numbers are fine.

Since your numbers seem very conservative, I'd be looking very closely for worn components. Something is allowing that R/F to toe excessively, it would seem. And don't forget about the rear, as under load it will effect the front as well.

Some measuring wouldn't hurt; cross for frame damage, and a tram check.

viperbob

Check the lower a-arm bushings.... I just replaced a set of arms with RS ones this week. Also, your caster is little low. Generally with this setup, I have it in the 5.2-5.4 area.

TheOtherEric

In case you decide to replace the front lower a-arm bushings, you might want to check out Powerflex urethane bushings. I just had them installed them this week, so I don't really have any comments about them yet. But they're just $180. See:
http://www.powerflexusa.com/
http://www.powerflex.co.uk/
http://www.bimmerworld.com/ (their U.S. distributor)

dwe8922

Thanks everyone for the ideas. The front a-arm bushings don't look worn, but then again, neither do the rear (and they are). This might be the answer, as the alignment specs are the same right to left, and the left tire (track tire) wore evenly across, unlike the right. I will definately remeasure to rule out any kind of frame damage.

As for caster, I know what it is, but I don't understand it very well, or how it affects things. What kind of change would occur by going to the higher number?

I am very interested in the powerflex bushings. I have been preparing to replace the rear bushings for a while now. I looked at their site, but didn't see anything for the rear suspension. From what I understand, one can't buy bushings only from porsche, and I don't know of anyone who sells the rear bushings aftermarket (racers edge?). Do any of you know of a source, or if powerflex makes a set for the rear? I also thought about solid bushings, but I drive it a lot on the street.

Thanks again,
David

RedlineMan

Hey;



Caster is the angle formed by a line drawn through the upper and lower steering pivot points, the strut bearing and ball joint in our case. Positive caster is angled back at the top. The more positive caster you have, the higher the stability at high speed. Because the strut is tipped back, road irregularities are transfered through the suspension to a greater degree. Otherwise, the wheel would simply deflect sideways (pull). Positive caster also increases steering effort, thus also damping road irregularities by increasing mechanical dissadvantage. It also effectively increases negative camber as the wheel is turned.

Think of trying to push a pencil accross a desk top, eraser end down. If you lay it back, it will slide. If you angle it up gradually, sooner or later it will catch and tip over. That's caster!

viperbob

I know that ERP sells a monoball for the rear, but for only one of the two bushings.

bobt993

I am in the same place, but different application. My car's suspension has been moving around and with the addtion of a cup coil-over, I am now installing monoball bushings. This would be track only application. ERP is the main supplier, but expect to wait and pay more for the bushings than your PSS9 cost. TRG can supply the ERP bushings. I was told you also might need bump steer correction depending on the ride height.

Do any of you know of a source, or if powerflex makes a set for the rear? I also thought about solid bushings, but I drive it a lot on the street.

Thanks again,
David[/QUOTE]

viperbob

TRG does not sell much ERP anymore...