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Brian Beckman: The Physics in Games - Real-Time Simulation Explained
Sim Racing Articles, Setup Tips & Guides

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 also.

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.”

High performance virtual racing products and how they can make you go faster.

Sim Racing Articles
Brian Beckman's - The Physics of Racing

The how's, why's and wherefore's of punting a car around a track... the entire Physics of Racing Series (PhoRS) by Brian Beckman, PhD, reproduced here with permission.

Introduction to the PhoRS article series
Weight Transfer
Keeping Your Tyres Stuck to the Ground
Basic Calculations
There Is No Such Thing as Centrifugal Force
Introduction to the Racing Line
Speed and Horsepower
The Traction Budget
Simulating Car Dynamics with a Computer Program
Straights
Grip Angle
Braking
CyberCar, Every Racer's DWIM Car?
Transients (The missing episode)
Why Smoothness?
Bumps In The Road
RARS, A Simple Racing Simulator
"Slow-in, Fast-out!" or, Advanced Analysis of the Racing Line
"Slow-in, Fast-out!" or, Advanced Analysis of the Racing Line, Continued
Space, Time, and Rubber
Four-Point Statics
The Magic Formula: Longitudinal Version
The Magic Formula: Lateral Version
Trail Braking
Combination Slip
Combination Grip
The Driving Wheel
Four-Wheel Weight Transfer
Hazards of Integration
A Magical Trick

At the top of the page you will notice a video by Brian Beckman talking about real time tyre simulation and the problems that arise, it really is an interesting video. If you are an iRacing subscriber watching this video it might help you to understand more about the New Tyre Model being developed and also where it is at and the forseeable problems that may arise...

Thoughts on Brian Beckman's comments relating to low speed behavior by Todd Wasson

iRacing driving school videos

Intro video for the iRacing Driving School
iRacing Driving School Chapter 1: Introduction to the school
iRacing Driving School Chapter 2A: Vehicle Dynamics
iRacing Driving School Chapter 2B: Vehicle Dynamics
iRacing Driving School Chapter 3A: Fundamentals of the Racing Line & Cornering
iRacing Driving School Chapter 3B: Fundamentals of the Racing Line & Cornering
iRacing Driving School Chapter 3C: Fundamentals of the Racing Line & Cornering
iRacing Driving School Chapter 4: Using Your Eyes
iRacing Driving School Chapter 5A: Braking Technique
iRacing Driving School Chapter 5B: Braking continued
iRacing Driving School Chapter 6: Downshifting
iRacing Driving School Chapter 7A: Race Craft & Passing - Understanding Race Craft
iRacing Driving School Chapter 7B: Race Craft & Passing - Technique
iRacing Driving School Chapter 7C: Race Craft & Passing Etiquette
iRacing Driving School Chapter 8A: Race Starts - Surviving Turn 1
iRacing Driving School Chapter 8B: Race Starts
iRacing Driving School Chapter 9: Pre-Race

Suspension plays a vital role in managing aero, so if a constant ride height can be maintained the car’s aerodynamics will work better.

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