Front Upper Control Arms...

MaysEffect

That is equally vague. 32-38psi covers a huge variety of load ranges of about 300ibs per axle. 2 degrees of camber variation is also a huge margin for both steering geometry and tire contact. Changing the caster by that amount (4 degrees to 6 degrees) would possibly change your camber at full lock by 1-4 degrees.

This also doesn't take into account the wide variety of suspension setups these tire companies are advertising to. Cars without sway bars, cars with solid rear axles, cars with McPherson struts.

None of this is a problem for the Z. So additional caster AND camber is not a necessary change, its the reason nissan knocked the Z34 down to -+5 degrees of caster. If you want more response out of the tires, properly match the SR for the given wheel/tire you are trying to use. Not an easy thing to do when dealing with clearance and fitment issues (brakes or fenders). So yes, this is the ultimate compromise. Adding caster and camber ruins your instantaneous roll center. Something that will severely compromise how the suspension balance SHOULD be setup.

ValidusVentus

Could you explain or provide a link explaining this. We have gotten slightly off topic on the thread but its a good discussion. I'm going to do some research on my own regardless.
I am currently at +6deg caster and -2.2 camber up front I believe. IIRC it wasn't possible to get more caster with the SPL arms without forcing the other variables off, though I was under the impression -mostly from scuttlebutt- that even more caster would have been favorable and was seeing this as a limitation for the SPL arms. I know I need additional camber all around (from tire evidence) but I still drove it on the street a bunch over the last few years in Cali; with no AC/blower/interior, race seats and a full cage. Now I'm up in Washington its a different story.

I don't want to turn this into another "what's the best suspension settings!?" thread but I think there is an opportunity to learn something here.

__________________
Mods: Dedicated caged track car, lots of things. ||| Valkyrie Autosport |||

MaysEffect

I think the discussion is well within the original scope of things. All these problems stem from the concern of rise/fall...weight jacking, and tire traction loss.

Compromised instantaneous roll center is the dilemma behind having too much rise/fall with "incorrect" front wheel geometry. Increased SAI, increased camber and increased caster will be the biggest upsets for this. The notion behind adding as much caster as possible is to get as much camber as possible, but at the cost of reduced pitch control (rise/fall). There are several workarounds for this. One of which is Hotrodz common choice of removing the rear ASB. The other is playing around with rake. The most uncommon is reverse rake, usually only seen on WRC cars and drift cars. The least common setup is reducing the front ASB stiffness.

Like Rusty eluded too, there are trade offs and compromises. Too me...adding caster AND high levels of camber are not ideal trade offs. -2 degrees of static camber is probably the most optimal setting if you are going to the route of increased caster, the issue is when you starting getting close to -3 degrees and around 7+ degrees of caster. Right now you are currently in a safe zone.

The issue is much more evident on low profile tires or tires smaller than the rim width and setups with positive SR values.


PM me if you want links and guides on the roll center issue. There are a lot of references.