What is Anti-Roll Bar (ARB) Asymmetry?
In an effort to increasingly make the stockcars more similar to their real world counterparts, we’ve decided to add an additional tuning parameter to the three top NASCAR stockcars – front and rear ARB asymmetry.
Every race weekend NASCAR race teams try to decide on how to best set up their front and rear suspensions with configurations that will allow for maximum front end travel, control body roll and have good handling. To accomplish this, in addition to springs and control arm geometry, ARB arm geometry is today an integral part. As these cars are setup asymmetrically from side to side with suspension geometry, springs, shocks, tires and weight distribution on ovals it also probably comes as no surprise that ARBs can also be setup to work asymmetrically. This means their arm geometry from one side of the car to the other differs by some margin (differing motion ratios) and controls how much the anti-roll bar diameter impacts either side. For example even a perfectly symmetrical car one will notice that under heavy straight-line braking the left side will travel more than the right side with large front ARB arm asymmetry. What is happening is the asymmetry is essentially tricking the ARB into thinking there is some amount of roll in the car to the right, while there is actually none, and engages the bar which in turn rolls the car to the left! What this can do in the front is help control how the splitter travels relative to the race track surface. Say if the left side is higher than the right side, or rolled up, more front ARB asymmetry will ‘pull down’ on the left front and ‘pull up’ on the right front and flatten the splitter out with respect to the track. Vise versa as less front ARB asymmetry will help solve a left front over travel problem by allowing the left front to travel less.
In the rear, more bar asymmetry can help replace large spring differences and effectively hold up the right rear end during hard cornering, but quickly disengage while driving off the corner, as load and roll drops off, helping turning in the middle and stabilizing exit drive off.
iRacing has decided to allow the members 6 different levels of asymmetry to allow custom control of their ARBs. Choosing how much ARB asymmetry you need or want (if any) is dependent on the rest of your setup, but it can be used to fine tune how and how much the anti-roll bars engage.
Please note that rear ARBs are not allowed on the Impala B as the real Nationwide Series disallows the use of a rear anti-roll bar also.