anti-roll bar (sway bar)

Sometimes referred to as roll bars or anti-sway bars. As a car turns, the cornering forces cause the chassis to lean, or roll, toward the outside of the corner. The amount of chassis roll needs to be limited in order to keep side‐to‐side tire loading and the camber of the tires in the optimal range. The anti‐roll bars combine with the wheel‐springs to do just that. Anti‐roll bars are transverse springs designed to act only when the car is rolling; they may be fitted to the front or rear axle or both. The primary function of the anti‐roll bar is to adjust the understeer/oversteer balance of the car during cornering, which it accomplishes by fine‐tuning the amount of load that transfers to the outside tires at the front versus the rear. A stiffer anti‐roll bar at one end of the car will increase the load on the outside tire at that end. If both bars are made stiffer, the load transferred will remain the same, but overall chassis roll will be reduced, which may require a camber adjustment. Remember, one of the primary goals is to find a good balance between grip at the front and rear of the car. When adjusting the roll bar settings the higher number represents an INCREASE in roll resistance, in effect making the car stiffer. Some cars only have a front anti‐ roll bar, and on some cars, the rear bar can be disconnected. Some cars have no anti‐roll bars at all, in which case any tuning of roll stiffness must be done with the regular wheel springs. Sway bar settings are mostly driver preference. There is no wrong answer or sweet spot. When you like the car’s attitude mid‐corner the sway bar is doing its job. Changing the sway bar diameter gives bigger changes in bar stiffness. For finer adjustment, use the sway bar arms. The advantage of using an ARB to adjust roll stiffness is that it can be changed or adjusted much quicker than a suspension spring, that it effects only the roll resistance rather than the multiple parameters that the spring rate effects, and that using an ARB allows for a generally softer, more compliant suspension for a given roll stiffness than using regular springs alone.


Anti‐Roll Bar (ARB) or Sway Bar diameter: A powerful tuning tool to affect the overall behavior of the car. A larger diameter bar is stiffer than a small diameter bar, with the stiffness proportional to d^4, thus even small diameter changes have fairly large stiffness effects. The material the bar is made from also effects stiffness, with a steel or “Fe” bar being stiffer than a titanium or “Ti” bar of the same diameter.

Sway bar or ARB Arm Length: Changing the arm length fine‐tunes the stiffness of the sway bar. A shorter arm will enhance the sway bar’s effect on cornering. This increases the bar’s effective stiffness by reducing the length of the lever‐arm through which the wheel acts on the bar. A longer arm will lessen the sway bar’s effects. Sometimes this adjustment is indicated directly as soft, medium, and stiff (or firm), and sometimes it is indicated by a number adjustment. When a number is used, higher values are stiffer. On many race cars this is the only anti-roll bar adjustment, and a generic soft, medium, stiff ARB adjustment normally indicates that the stiffness adjustment is being made by changing the length of the ARB arms or where the ARB mounts attach to the ARB (thus changing the effective length).

Left Bar end offset: Offset is how is how sway‐bar gap (discussed immediately below) is determined. [Per Setup guide - need some more explanation & tuning tips]

Attach left side: [its unclear to me what this is/does - need some help to fill in the gaps] Is this just a detached sway bar option? Why not do like road racing cars, with “detached” being an ARB arm option or “none” a diameter option?

ARB pre load: [need some more explanation & tuning tips] Equivalent (at least effectively?) to bar gap? Combine them/use this clearer adjustment in place of the bar end offset + bar end clearance? Effect of pre-load / proper tuning of this setting?


Sway bar gap/Left bar end clearance: The sway bar gap setting is measured on the left‐front suspension. Where the sway bar arm connects to the lower “A” frame, there is an adjustable Heim joint. This Heim joint determines the sway‐bar gap. In iRacing, sway‐bar gap has positive and negative measurements. Negative measurements mean the sway bar is loaded and will act as an anti‐roll bar immediately upon left‐ and right‐hand steering inputs. This will make the car less likely to rotate or turn. Load can increase comfort on a car that is loose on entry. Positive numbers means the sway bar is not loaded. The gap will allow a certain amount of roll to occur as a result right‐hand steering inputs before the anti‐roll bar will begin acting on the suspension. Increasing this number will make a car rotate heavily on entry and turning ability will increase throughout the rest of the corner. A neutral bar will have a setting of 0. Sway bar gap is typically a setting of driver preference. Find a spot you like and remember that this setting is highly affected by many other changes within the garage. It is imperative you keep a good watch on your sway bar gap as it is likely to change drastically with minor adjustments to the car’s other components. To avoid unintentionally changing your sway bar gap, set it to a large positive number (large gap), make your other adjustments and then re‐adjust the sway bar gap to your preferred setting. [Per Setup guide - need some more explanation & tuning tips, maybe streamline this complicated and unclear description]

Tuning advice

Just like spring rate, you want to run as soft an ARB as possible while maintaining sufficient control of the car and body roll and the proper handling balance. Softer settings lead to more compliance and more grip on that end of the car. They also tend to be slower responding and easier to drive, but stiffer settings can be more stable and faster responding.

(1) Stiffer: Will increase overall car stability (reduces roll) and shift the car’s balance toward UNDERsteer (push), thus allowing the driver to be more aggressive with the steering. The compromise can be on bumps and/or braking. A stiffer front bar will reduce compliance, so when one tire hits a bump the entire front axle will be affected through a loss of overall grip.
(2) Softer: Allows more roll and will shift the cars balance toward OVERsteer (or less UNDERsteer.) And the front will improve in compliance, which improves performance in brake zones and over bumps.

(1) Stiffer: As you add throttle through the corner while the steering wheel is still turned, the rear anti‐roll bar becomes very effective. Stiffening the bar supports the rear and shifts the balance to less UNDERsteer at corner exit. Again, the compromise is in compliance; a possible SNAP or FLAT OVERsteer may result if rear anti‐roll bar is TOO stiff.
(2) Softer: Allows more roll at the back of the car, which will be most evident at corner exit. If the bar is TOO soft, the car will exhibit exit OVERsteer. In this case, compared to a rear bar that is TOO stiff, the exit OVERsteer condition will be more gradual instead of a snap, hence the phrase “roll OVERsteer.”


The roll control effects of an anti-roll bar or sway bar are similar to the effect of changing spring rate (in effect an ARB is just a special kind of torsion spring), thus the roll stiffness of the ARB is often traded back forth between spring rate to determine the optimum compromise. Stiff front anti-roll bars can also lead to increased front inside front tire lockup under braking.

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