Here's what I've gathered so far:
1. The stock
control arms flex under hard launches, which can cause wheel hop. If you peel out and it sounds like a rapid sequence of chirps, you have wheel hop.
2. The stock rubber bushings flex and compress a lot, allowing the arm to twist a little. This is by design.
3. Polyurethane bushings are hard and barely flex. They will allow up/down movement of the arm and very minimal twist. This is good in keeping the axle in place, but is hard on the chassis.
4. Spherical bearings are solid and do not compress. They allow full up/down and twisting movement. They do not absorb vibration or noise. Some say the ride is noisy. Some say they didn't notice a change.
5. Some
control arms have polyurethane bushings on both ends. These (I think) are best for the drag racer since the flexing of the control arm is the main concern. The axle can move up/down and very minimal side/side.
6. Some
control arms have spherical bearings on both ends. These (I think) are best for the autocrosser since they do a better job at keeping the wheels planted on hard cornering. (I'm still not clear on how that works).
7. Some
control arms have one of each. Maximum Motorsports and Pro3i have the spherical bearing at the chassis and the polyurethane bushing at the axle. Global West and UPR have it the other way around. (I'm not sure which one is better and why).
Hopefully someone can correct and/or add to this.
