What is Anti-Roll Bar (ARB) Asymmetry?
In an effort to increasingly make the stockcars in iRacing
as close to their real world counterparts as possible iRacing added 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 best to 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 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
Axle/Truck arm assembly preload
Axle/Truck arm assembly preload is the amount of torsion loaded into the axle and truck arm suspension assembly. As the assembly is
oriented by different tire sizes left to right and truck arm mount positions twisting load is introduced. The adjustment in the garage
is meant to represent a way to relieve that torsion with changes akin to changing pinion angle shims installed between the ridged
connection of the truck arms and the axle housing.
ATLAS Express Data Analysis Software (Telemetry Software)
iRacing.com, the world’s leading online motorsports simulation service has a partnership with McLaren Electronic Systems
to incorporate the ATLAS Express data analysis software into its system. This allows iRacing’s 25,000+ members to use a
similar data acquisition and telemetry software used on every car competing in the FIA Formula One World Championship
since 2008 and on NASCAR’s standard ECU (engine control unit) in 2012.
“With the new iRacing telemetry capability, our members will be able to log detailed telemetry from their virtual race
car to disk,” says Dave Kaemmer, iRacing’s chief executive and chief technical officer. “Using McLaren Electronics’ Atlas
Express data analysis application, members who wish to delve into the engineering details in order to improve their cars’
handling will be able to do so, using very similar tools as F1 and NASCAR teams. In addition, with iRacing’s new
real-time telemetry interface, multiple applications will be able to access telemetry simultaneously, allowing easier
support for motion platforms, external gauges, and other add-ons from the sim-racing community.”
ATLAS Express is derived from the ATLAS suite of software developed in the 1990s to support McLaren’s own Formula 1 team.
Continued growth and development of the system saw it introduced into a variety of motorsports environments including Le
Mans and ALMS sports cars, the FIA World Rally Championship, the FIA Formula One World Championship, NASCAR and IndyCar.
The FIA awarded McLaren Electronics the contract to supply the powertrain control system to every team competing in the
Formula 1 from the beginning of the 2008 race season and, in February this year, NASCAR named McLaren as the Official
Engine Control Unit of NASCAR for the 2012 Sprint Cup series in support of its impending switch to fuel injected engines.
“Up to now, you had to be a race engineer in a top level race team to access these tools” says Mike Phillips, President of
McLaren Electronic Systems’ US division, “and access to reliable real-time data has been a game-changer for car
development and race strategy in recent times. Our link with iRacing will now make this experience easily accessible to
the current user community and hopefully new players intrigued by the possibilities this gives them.”
In its iRacing
application, ATLAS Express makes available substantially more detailed information regarding performance
such as the real time tire surface temperatures, along with critical data such as lateral acceleration, steering wheel
angle and damper/spring deflection.
“Up until now, our members have only been able to work on their setups by ‘feel,’ tire wear and temperatures, and by
gauging their performance on the stop watch,” says Kaemmer. “ATLAS Express will now allow iRacers to view driver and car
performance in a given session to help them tune the car with actual data.”
“Although engineering a race car is an interesting challenge, iRacing will continue to provide ‘Arrive and Drive’ racing
series with fixed car setups for those who prefer turning a steering wheel to turning a wrench. As has always been the
case, members will be free to share their set-ups with other iRacers, so the addition of ATLAS Express to the service
figures to make everyone a little – or a lot — faster.”
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