An old post but I really must comment on the issues raised in several posts above. The geometry of the rear suspension is really an upper "wishbone" and a lower similar wishbone. The main problem is that these upper and lower arms do NOT pivot parallel to the car centreline. They pivot at an angle to the centreline hence are called semi trailing arms. Effectively the wheel will toe out as the suspension compresses. The tricky bit is that the upper L arm, effectively a wishbone, has a different trailing arm angle than the lower wishbone. This means that the spindle(knuckle) rotates as the spring compresses. The knuckle moves forward a bit and importantly the top part moves forward slightly less than the lower part. Hence the BMR video of a Camaro driving down a road looks as though there is massive rotation about the lower control arm joint. Reality is that the rotation is simply happening due to the semi trailing arm geometry mismatch top compared to lower arms.
Given that the knuckle moves forward ( about 12 mm) as the spring compresses, because the toe arm and the trailing arms are bolted to a cradle, it must cause the bushes to squish up, or the arms themselves must rotate slightly in torsion. That is why GM makes both arms weaker in one direction, to allow for the geometry change that must have twist either in the arm, or in the joints. Making both stiff is asking for trouble.
If solid, or stiff joints are used in the knuckle at the trailing arm, as BMR suggest for their dedicated drag car, than the knuckle cannot move to allow toe adjustment. For the toe arm to make any difference to the wheel, it must lengthen or shorten its length. The knuckle must then rotate slightly, and this happens about the control arm spherical joint. So if there is a rigid joint at the trailing arm in the knuckle, then the knuckle is stopped from making any toe change.
A similar distortion happens if stiff poly is used at all of these arm locations. The geometry dictates that there must be movement somewhere to allow toe change. The other very important geometry issue is that the lower arms, effectively a wishbone, pivots about a plane formed by connecting the midpoints of the inner joints. This plane is NOT parallel to the bolts at these inner joints. The pivot plane is at a considerable angle to these bolts. This means that as the wishbone rises or falls, it MUST deform the bushes, or else it will freeze up. Poly will take deformation for awhile, but not forever. Eventually it gives up and forms an oval shape. Rubber bushes will deform for a very long time, but their downside is that they allow movement, as indeed they must to obey the geometry.
Using spherical joints at the inner joints satisfies the geometry issue. However there must be at least one deformation joint at the knuckle to allow for toe adjustment. The issue of the twist in the toe arms and trailing arms due to the whole wheel moving forward due to the semi trailing arm geometry is satisfied if inner joints are spherical joints as the pivot plane is not governed by the bolt directions. The arms simply rotate nicely over their spherical ball.
So I take issue with the use of high duro poly at suspension joints. Poly is not like rubber and cannot take deformation for long before becoming oval. Poly joints are designed to rotate perpendicular to the arms, in the direction of the bolts through them. Once the arms pivot at an angle, you are on borrowed time before ovality becomes an issue. Seems good initially, but poly fails eventually.
All this means that the outer trailing arm joint should have some flexibility in it for toe change to occur. The inner joints would be great if spherical joints were used, but the downside of noise may be an issue. In Australia, exposed rod ends are not legal for road use due to rapid wear if dirt falls on the joint. Legal spherical joints need to have a rubber boot. The camaro lt1 toe arms, part number 22845487 have spherical joints, and the arms themselves are the same size to allow for torsion. However, if spherical joints are used, there is not a need to have twist in the steel arm.... I guess they just wanted to save money. Using these LT1 arms, at $70 each, seems a bargain.
There does not seem a way to have a decent outer trailing arm joint, but I would think a stiff rubber joint would be the best option, certainly better than poly. Wheel hop, we call it tramp over here, remains the biggest deficiency in this G8/VE/VF platform. I note that firms claiming success in curing the hop never mention the behaviour in wet weather. Hop is way more prevent in wet roads due to lower adhesion limits, and is the only true way to judge if the issue has been fixed properly. No wheel spin = no hop. Hence once you have traction it is not an issue. However, wet weather will soon determine if the suspension mods actually do anything. I find it frustrating that firms claim success in curing hop, but when pressed, all fail to explain why their "cure" still hops in that oscillating time between adhesion and wheel spin.
As a point of interest, the latest HSV GenF, that uses the G8/VE platform, uses the ZL1 engine and the ZL1 rear suspension. 4 bolts is all it takes to fit the rear cradle. It has the big/ small axles, the spherical joint toe arms, the spherical joint in the knuckle for the lower and top control arms too. It uses the rubber outer trailing arm joint, as per the above explanation. And it wheel hops too!!! The solution offered to hop, is the same as for the ZL1, and that is to use electronics to stop wheel spin, hence no opportunity for stored energy to release. The electronic throttle is closed down to maintain traction. BMW, and Mercedes do the same thing as none so far can come up with a mechanical solution to IRS hop. Check out hopnot.net for a better solution that seems to work for SRTs, in the wet as well.