Originally Posted by afm

Rear Camber Links & Roll Center

The following generalizations apply in most cases.
1.-An upper link that is parallel to the lower A-arm will make the Roll Center sit very low when the car is at normal ride height, hence the initial body roll when entering a corner will be big.
2.-An upper link that is angled down will make the Roll Center sit up higher, making the initial roll moment smaller, which makes that particular end of the car feel very aggressive entering the corner.
3.-A very long upper link will make that the roll moment stays more or less the same size when the chassis leans over; and the chassis will roll very deeply into the suspension travel. If a lot of camber is not used, this can make the tires slide because of excessive positive camber.
4.-A short upper link will make that the roll moment becomes a lot smaller when the chassis leans; the chassis won't roll very far.

In general, you could say that:
1.-The angle of the upper link relative to the A-arm determines where the roll center is with the chassis in its neutral position
2.-The length of the upper link determines how much does the height of the Roll Center changes as the chassis rolls.
3.-A short, angled down link will locate the Roll Center very high, and it will stay high as the chassis rolls. So the chassis will roll very little.
4.-A long, angled down link will reduce the car's tendency to roll initially, but as the chassis rolls it won't make much of a difference anymore.
5.-A long, parallel link will locate the Roll Center very low, and it will stay very low as the car corners. Hence, the car (well at least that end of the car) will roll a lot.
6.-A short, parallel link will make the car roll a lot at first, but as it rolls, the tendency will diminish. So it will roll very fast at first, but it will stop quickly.

In terms of car handling, this means that:
1.-When the link is angled down (higher Roll Center) gives the most grip initially, when turning in, or exiting the corner,.
2.-When the link is angled up (lower Roll Center) gives the most grip in the middle of the corner.
3.-If you'd like more aggressive turn-in, and more low-speed steering, set the rear upper link at less of an angle.

What's the best,
A high Roll Center or a low one? It all depends on the rest of the car and the track. One thing is for sure:
1.-On a bumpy track, the Roll Center is better placed a little higher; it will prevent the car from rolling from side to side a lot as it takes the bumps, and it will also make it possible to use softer springs which allow the tires to stay in contact with the bumpy track.
2.-On smooth tracks, you can use a very low Roll Center, combined with stiff springs, to increase the car's responsiveness.

FAST GUIDE CHART
Long Link
A long link gives a lot of body roll in turns.It feels as is the body is willing to keep on rolling, until in the end, the springs prevent it from rolling any further.The car has more grip in corners, especially the middle part. But: if there already is a lot of traction, long camber links can slow the car down in turns.
Short Link
A short link makes that the body doesn't roll as far, its tendency to roll drops off as it rolls.It feels as is the car generates a little less grip.
More Parallel Link(to lower arm)
A parallel link gives a little more roll than an angled one.It feels very smooth, and consistent as the body rolls in turns.
Angled Link(Less Parallel to lower arm)
An angled link makes it feel as if the car has a tendency to center itself (level, no roll), other than through the springs or anti-roll bar.It gives a little more initial grip, steering into corners. It makes it very easy to 'throw' the car.The body rolls a little less than with parallel links.It's possible to use softer settings for damping and spring rate than with parallel links, without destabilizing the car.
Longer Rear
More rear traction in turns, and coming out of them.Rear end slide is very progressive, not unpredictable at all.Make sure that there's enough rear camber though, or you could lose rear traction in turns.
Shorter Rear
The rear feels very stable. It breaks out later and more suddenly, but if it does, the slide is more controllable.It makes the front dive a little more, which results in more steering, especially when braking.
More Angled Rear The rear end is rock-solid while turning in. It feels very confident.

AFM