Over the past 2 years i have had a number of alignment setups done to my GT4. I noticed that caster had a crucial role in how the car handled on track. One of the first mods i did was to increase front camber via shims. Adding shims for camber gain also impacts caster. I also lowered the car (three full turns of the adjuster all around) at this time. This resulted in a lack of front end grip which had me confused for a long time until i realized that GT4 oem caster numbers were not published. At that time my caster numbers were around 9-9.3 range. I went ahead and ordered adjustable thurst arms and set the alignment again and adjusted caster to 10. The result of this change was HUGE. The car went back to being balanced, good turn in, midturn grip came back and overall much easier to drive.

 

That's really interesting. I recently had my car aligned for the upcoming Smokies event. Used shims to set the front camber to -2.5 (strut top all the way inboard) and the caster fell in at 10.

 

I have -2.5 camber in front with shims- 17mm total each side including the bracket. Strut tops all the way in. Caster came in at 10.2 deg. My alignment sheet shows the oem caster spec as 9.5 to 10.5 deg. Alignment done by local dealer.

 

I had a similar experience. When I switched to the Tarett camber plates to get the car to -3.5 front camber without the motorsport-style lower control arm bushings, I removed a lot of caster. I think they had trouble getting the car to 5 degrees of caster. Despite going from -3 to -3.5 camber, the car had more understeer and the front tire wear was worse. Caster gives you some negative camber on the loaded tire in corners, which is a nice time to get it. It also allows you to run less static negative camber, which will improve braking. Too much caster can cause mid corner/exit understeer. There is obviously some science and art to setting up a porsche - some people seem to allude to caster being a secret sauce.

Moving to Tarett's new plate design help us get back some caster. I was a bit miffed with the experience because Ira was not willing to trade out what I considered to be a design incorrectly sold as an option for the GT4 with the newly designed plates. I had just discovered the problem with the old plates, when they announced that the new design would be available in July. In any case, early adopter 1st world problems - I have those a lot. Tarett makes very high quality stuff and Ira knows his stuff.

If you're trying to center the wheel in the fender, you will be removing some caster to do it. As you swing the lower control arm back with the thrust arms/bushing, to counteract the forward position of the wheel due to adding shims, it rotates the upright CCW removing some caster.

 

So you guys are saying more caster has provided good results? It seems then that for those running a low amount of front camber, no need for caster pucks. -2 to -2.3 camber up front should get you there.

Or do I have it backwards?

 

Just did an alignment this weekend and here are the numbers with everything stock except Tarrett drop links and TPC rear toe links. Caster fell in at around 10.