rbahr

Hi All,

I would like to understand what the correct setting the angle of the thrust bushings on both front and rear lower control arms? I am looking for 8.5 deg +- for the front, not sure what the rear should be.

Also like to know which hoe to use? The one closer to the center or further away

I have the Tarret bits.

Thanks

Ray

FFaust

Interesting question Ray.

I messed with this a bit when I did my last alignment this Spring, but ended up pretty much going back to the setting I had prior, 8 or 9 degs I think.

I was trying to get rid of some rubbing in the wells since my car is pretty low, but playing with castor made it worse, so I just tried to center the wheel.

Hopefully someone chimes in; whereas camber and toe are easy to understand and adjust, castor to me is a bit of a black art.

Macster

IIRC castor is 8 degrees +/- 30'. 8.5 degs will slow the car's reaction to the steering wheel a bit.

AFAK there is no castor callout or setting for the rear wheels.

For which hole to use doesn't Tarret offer some guidance? If not then and if no one can offer any guidance I guess you will have to pick a hole and check the alignment results and arrive at the right hole by trial and error.

Regardless of how you come by the hole choice you would have to check on the alignment rack the results of whatever hole you used to ensure the hole setting delivered the desired alignment numbers.

rbahr

Thanks,

The advice I got was to align the holes in the pucks with the thrust arm, with the hole closest to the center towards the front of the car. So this means that any force directed will tend to resist turning.

Thanks

Ray

rebrewer

I think unless you want a change, align the holes with the axle and go with the centermost hole, which is slightly off center. I have the Tarret center bushing replacements.

lordpantsington

Seems like If I post a reply it tends to kill the thread so I tried to let this stew for a bit before replying. Who knows, maybe something interesting would pop up? As far as rear castor goes, this is the only mention I've seen: https://rennlist.com/forums/porsche-...l#post10065537

rbahr

Thanks Andrew!!!!

The castor in the rear is difficult to measure - perhaps part of the problem.

Now, castor has an effect on the camber curve which is one effect... Bump is the other 800 lb gorilla in the room, but at least I know what that is supposed to be :-)


Ray

rbahr

So, I spent time with the 2012 RSR manual tonight and found this:



The castor is the length of the trailing arm, and a function of the wheel base.

Still leaves me with a few questions...

Ray

rbahr

Hi All,

Just got off the phone with Tim Olsen - Thanks Tim, and wanted to capture this info:

There are really 2 settings at each end of the car: Castor - both ends, anti-dive, and anti-squat.

So rear castor (as measured at caliper) is ~ 1.25 deg,
anti-squat - which is the distance from the tub for the thrust arm in the rear, is full up - eg: closest to the body (using the Porsche standoffs)

Front Castor is ~ 8.5 deg, and anti-dive should be thrust arm with longest standoff - move arm away from the tub!

Ray

lordpantsington

The 2012 RSR was the homologation special 997 with the super wide rear and cutouts in the rear quarter panels behind the doors. The '09 manual might be more appropriate to look at since it uses the same uppers as the GA/S. FWIW '09 lists wheelbase at 2370 mm max, Rear Camber -3.5°, 372mm rear trailing arm, 261mm Rear upper front wishbone, 255mm Rear upper rear wishbone.

rbahr

Thanks Andrew,

To reiterate, the 2009 997 RSR data






The lengths of these arm are just there to show that the Factory does have numbers...

Ray

lordpantsington

Just remembered that I stumbled upon Meyle's OEM parts catalog online and had noted lengths of the 996 GT3 parts, trailing arms at 370mm and UCA as 250mm (Also shown elsewhere as 251mm). Might be helpful for drawing relations.

GT2rainge

Very interesting thread, a subject I tried to look into myself but didn't really come up with any solid answers.
I understood that to properly set the rear puck position you need use a bump steer gauge.
I never really found out about what difference it makes to the camber curve etc and how this is best adjusted and what figures set too.
The dog bones length was another thing I tried to find out about the pros and cons but drew a blank also.
There's probably a lot too be gained from have it all set up correctly.
Ill keep an eye on this thread with great interest
Neil