GS mod, is it necessary?

[Jetset700]

I want to put improved UCA, LCA on stock sub-frame. Is most of
the geometry help in the arms or do I need the GS mod as well.
Also there is the spindle choice, those ATS ones look great but
I think thats beyond my needs.

[zo66]

check out sc&c i think the best bang for the buck

[CarlC]

Best bang-for-the buck: Guldstrand Mod. Aftermarket control arms will not make dramatic changes in the suspension geometry. Plus, the GM is free.

[vanzuuk1]

Carl Do you recomend both , or just gmod or control arms alone?

[Jetset700]

Thats my real question, both or one or the other.

[Marcus SC&C]

Upper arms make exactly no direct difference in suspension geometry at all by themselves. Our arms or anyone elses arms. The geometry is dictated by the pickup (or pivot) points of the suspension. The arms (upper or lower) just connect the dots.
Aftermarket tubular arms may be more rigid than stock arms for less deflection under load. They can (and ususally do) have the BJ plate or cross shafts moved rearward for more + caster. This helps straight line stability and auto centering to a certain extent.
Naturally our adj. tubular arms make getting the exact alignment specs you want not only possible but easy with any configuration.
This is important and will improve performance but not because the actual geometry of the front suspension dynamics (camber gain,RC location,FVSA etc. etc.) have changed to any considerable degree.
Anything that moves the suspension pickup points vertically WILL alter the actual geometry in a profound way. That`s where the G mod,tall ball joint packages (like our Stage 1 and 2) and tall spindles (like ATS) come in. Try to use these with stock arms though,made to work with the factory geometry,compound it by lowering the car and there`s a excellent chance you won`t have enough range of adjustment to get the alignment specs you need to make the geometry work well. They go hand in hand. To say nothing of things like ball joint bind in bump etc. That`s why we bundle the tall ball joints and adj. arms together into matched packages and why we`re working with ATS to provide adj. arms for their tall spindles. Mark SC&C

[CarlC]

What Mark said.

An A-arm change does not affect geometry. I ran the GM using stock arms with del-a-lum busings and it worked just fine.

[CarlC]

What Mark said.

An A-arm change does not affect geometry. I ran the GM using stock arms with del-a-lum busings and it worked just fine.

Mark,

My suspension pivot point understanding is very limited. Since most aftermarket A-arms do/may have additional built-in castor/camber, this could mean that the upper A-arm pivot axis may be farther ouboard vs. a stock arm. Does this make any difference in the geometry? For example, since less shims would be required to achive the same caster angle, the rotational axis is closer to parallel, and closer overall, with the upper mount.

[vanzuuk1]

Thanks mark and Carl.

[Marcus SC&C]

"Technically" yes but adding caster only moves the rear of the shafts inboard and the difference is so very small the geometry change would be very difficult to even measure let alone feel. Vertical changes have a MUCH more profound effect. Camber curves for example are eliptical. Horizontal changes will slightly alter the shape of the elipse (it takes quite a bit to alter them in a meaningful way because the largest changes are in the extremes of travel that you seldom use) but vertical changes dictate where in that elipse a given pickup is in relation to all the others. In this regard relatively small changes can make a significant difference. I`m way over simplifying this but that`s the gist of it. Mark SC&C

[CarlC]

Thanks!

[David Pozzi]

The "better" tubular upper arms allow around 5 degrees positive caster to be used, this tips the wheel in at the top when you turn, it's like negative camber that only happens when you turn the wheel, a good thing when cornering but when pointed close to straight-ahead, the wheels don't generate any negative camber unless the Guldstrand mod is done.

So, my thinking is, the Guldstrand mod mainly helps on large radius turns, where the wheels aren't turned very sharply, the car leans a bit and the Guldstrand mod generates more neg camber and helps keep the tire flat on the pavement. It doesn't quite keep up with body roll though.

The extra positive caster helps when the wheels are turned, the more turn angle, the more the wheel leans inward at the top. I'd assume the high caster setup helps most in slower tighter turns, but would also yield a little help on large radius turns.

[Marcus SC&C]

Well said David. That`s why we like to combine camber gain and RC height improvements in the form of our tall UBJs,the G mod or both with fully adjustable arms to allow more + caster as well. That way it covers both high and low speed turns,why compromise when you don`t have to? Also bear in mind that modern performance cars have proper camber curves AND run a good amount of + caster (most more than 5*) to attain their performance. Mark SC&C