NASCAR iRacing Series Open Garage: Bristol
August 21st, 2014 by JaimeB
If you drive north of Knoxville on Highway 81 you will pass a number of small towns. One you just might miss if you blink is Bristol, Tennessee. With a population less than the number of people in attendance at most college football games, it seems an unlikely setting for the fourth largest sports venue in the United States. With its high progressive banking and short length plays, however, Bristol Motor Speedway plays host to some of the most exciting – and popular — racing on the NASCAR circuit; what’s more, BMS’ proximity to the Carolinas make it a local track for the many teams who call the area home. On race weekend fans flock to the 160,000 seat venue heralded as “The Last Great Coliseum” to produce one of the greatest spectacles in motorsports.
With three weeks of sim racing to go in the NASCAR iRacing season, championship points are getting more valuable each race. Making sure your car rotates well through the corners and is stable on exit here at Bristol is important, not only to be able to control your car well enough to avoid the inevitable pile ups that occur here, but to prevent the car from over-rotating on exit and slamming head first into the inside wall on its own.
While on most short tracks you would dive into the low lane, allow the car to rotate and drive off the corners, here at Bristol there are several bumps on the lower lane which upset the chassis causing the driver to have to slow the car to maintain control. This is magnified if there is traffic on the high side. Try running a middle or higher line, allowing the car to drift a small amount in the center, then dip slightly into the last part of the corner before driving off. This will allow you to avoid the bumps on the low lane and improve your overall lap times.
This week running the stock Gen6 setup, I felt the rear end of the car over rotated, making it feel unpredictable and snap loose. I also noticed there was a lot of room in the oil and water temperatures leaving the ability, if preferred, to run a higher gear allowing for more pickup off the corners. Keep in mind though that as you increase the gear ratio the throttle will be more sensitive, and your temperatures will run hotter.
Looking at the tire temps and setup sheet after running the stock setup for a few laps, I noticed the caster was oddly set with the left front forward, and the anti-roll bar asymmetry was set to max. Much like with the shocks or weight distribution, should I find a setting maxed-out I immediately think that this was done to try and compensate for a problem with the car’s handling. I usually look for a way to produce a similar effect to allow me some play.
To understand where we can make an adjustment we must first understand how the front anti-roll bar (ARB) works, what is meant by “asymmetry” and how changes affect the car. The ARB is a bar connecting the left and right suspension. Used to control body roll, the ARB counters the g-forces forcing the car’s body to roll from one side to the other. “Asymmetry” means the arm geometry from one side of the car to the other differs by some margin. Adjustments to this setting can be used to control how much the anti-roll bar diameter impacts either side as well as the way the splitter travels relative to the race track surface
For example: a “symmetrical” car is a car setup evenly/identically from side-to-side. If we were to increase the mounting position on the right side of the car we create tension on the anti-roll bar. What is happening is the asymmetry is fooling the ARB into thinking there is body roll to the right which forces it to engage the bar attempting to roll the car back to the left.
This week practice running the middle and high lanes to see if you can pick up some speed. Try running the stock gear and one higher to see if the extra response and pickup increase your lap times. Use tape to fine tune temperatures and a combination of track bar, weight distribution and brake bias to help control the rear end.
A conservative setup here may lack a little speed, but in a crowd it may just provide the control you need to avoid the inevitable carnage that makes this place Bristol.
Good Luck and God Speed!