Front Upper Control Arms...

MaysEffect

That's an extremely vague suggestion that should be taken with a grain of salt.

Racing tires needed additional camber, adding positive caster is another way of getting more camber with additional steering lock. The tires dont need caster, in most cases its worse for the tires as it pulls the tire away from the road.

Increased negative scrub and wider tires is necessary if you increase camber and caster.

Rusty

A little info from Toyo tires.

Toyo Tires recommends the following general set-up guidelines for the Proxes R888:

Operating Temperature: 160°F to 220°F
Hot Inflation Pressures: 32 to 38 (psi)
Camber: -1° to -3°
Caster: As much positive as possible

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Hotrodz

My r888 setup:
Hot Inflation Pressure: less than 36 psi tire will get squirrelly 36 psi or better.
Camber: -2.26 front -2.00 rear
Caster: 6.5 and I think 7 to 8 would be better

There was another member here running -3.3 front and -1.8 rear with caster at 8 for the same tire. He was running 18x315 and I am running 18x295.

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Rusty

Yeah, I'm running -2.0 camber and +7 caster front and -1.75 camber rear.

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MaysEffect

Have you tries 3 degrees with low levels of caster and less rake? and possibly different shock settings.

Hotrodz

No I have not. I am dialing things in slowly. I disconnected my rear sway bar and to help rotate the rear a bit more and so far I like. My next move was to add more negative camber, -2.8 to -3.0 since I don't do much street driving with her anymore. What do you consider low levels of caster?

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MaysEffect

5 degrees. I don't think i have any fair bases of suggestions for your situation though, you are well beyond the level of modifications to start making large dynamic changes again. Unless you like doing that...

My point was simply adding both camber and caster is not necessary for this chassis or the scenario of changing the SAI. It doesn't suffer from suspension limitations like some other cars with inferior suspension setups.

8 degrees of caster is up there with rally cars, and RX cars use low levels of camber for better steering linearity and tracking through loose gravel. Something that is not a issue for cars on tarmac.

It also comes down to how anyone adjusts driving techniques for the setup implemented. Caster levels and rake significantly changes steering feel. If you're making modifications to the suspension to alter this, then changing geometry again will just slow you down and cause confusion. If you're not wearing your tires out incorrectly then there really isn't really a reason to flip the script.

Hotrodz

Agreed, I am not looking to change much as my tire ware has been good. I'm looking for that balance of grip and handling. Which is a never ending chase lol!

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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.

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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.