Anti-roll bar
A torsion link between the two wheels of an axle that resists body roll without adding vertical stiffness. The front/rear split of roll stiffness is one of the primary balance levers: stiffening an end tends to make that end give up lateral grip earlier — a stiffer front tends toward understeer and stability, a stiffer rear tends toward rotation. Because springs also contribute roll stiffness, spring and bar changes should be considered together to keep the intended balance.
Effect by corner phase
The roll-stiffness split influences how eagerly the car takes its initial set on turn-in.
The stiffer end tends to slide first at steady state — the classic mid-corner balance lever.
A softer rear bar tends to help the driven axle keep grip as power goes down.
Symptom tendencies
These describe tendencies, not rules.
Mid-corner understeer Mid-corner
A softer front bar or a stiffer rear bar tends to move the balance rearward. Change one end at a time and re-test.
Snappy oversteer on quick direction changes Entry
A softer rear bar tends to calm the transient at the cost of some responsiveness.
Exit understeer — the car pushes wide as the power comes in Exit
A stiffer rear bar, or a softer front bar, tends to let the car keep rotating as the throttle opens. Expect a little less rear stability in the same corner — change one end and re-test.
Exit oversteer — the rear steps out as you pick up the throttle Exit
A softer rear bar tends to give the driven axle more roll grip on power; a stiffer front bar works the same direction from the other end. Both trade away some mid-corner rotation.
Verify on track before you commit to a change.