There are four ways of controlling roll;
1) roll centres - these control the transition, the way the car rolls. Get these right for the "balance" you want from the car.
2) Springs - ultimately these will limit the amount of roll you get (stiffer = less, softer = more) and thus the potential to generate grip. Obviously the roll centres have a part to play with this too.
3) damping - along with the roll centres these affect the rate at which the car rolls (stiff = slower, softer = faster)
4) ARBs - these are essentially additional springing but springs that react to roll only rather than bump too (a bit simplistic but generally ok as a starting point for discussion). Also where as most springs used in RC cars are near linear in response ARBs are more rising rate - the more roll the more they try to resist the roll.
There are instances when you need softer springs for weight transfer, bump handling etc. but could really do with more roll stiffness from the springs. This is where ARBs come in.
I often like to have the car setup softer for bump handling and weight transfer (for traction mainly) but use the ARBs to control the ultimate roll, sort of the best of both worlds.
ARBs can make the car feel very twitchy if they are too stiff relative to the springs they are paired with, its a balancing act.
Too stiff ARBs will also make the car less stable over very rutted surfaces where there can be large differences between wheel bump positions on an axle so don't over do it there.
Finally I often set up a 4wd car with a both front and rear ARBs (rear slightly stiffer than front) and if I am after a less twitchy car I usually can just pop off the front ARB and reduce that without upsetting the rest of the balance too much.
Really looking forward to the ARB kit for the RB6, that is going to make a big difference to that car and it's damn good already!
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