The wheelie bar adjustment is extremely critical to how the car reacts at launch. The function of the wheelie bars is to break the initial traction of the tire generating spin (tire speed) off the starting line.  As conditions become warmer (or as they deteriorate), the wheelie bars may be raised slightly, to compensate for the reduced traction available. 

Three final adjustments can be made at the last minute: to the clutch base pressure, to the clutch centrifugal pressure (counterweights), and to the wheelie bar settings. As the driver buckles into the race car, an inspection window on the upper right side of the bellhousing allows crew members access to make final changes to the base pressure and to the counterweight on the clutch.  If the sun goes in (or out), you will often find crew chiefs diving into the passenger side of these Pro Nitrous and Extreme Pro Stock cars to make these final adjustments, which could ultimately make or break a final qualifying attempt or elimination round. Crew chiefs spend a great deal of time sorting through computer data trying to optimize the initial tire spin off the starting line, and after the burnout you will often see them make an adjustment to the launch RPM.   The third and final adjustment is to the wheelie bars just before the driver stages the car. The function of the wheelie bars is to break the initial traction of the tire generating spin (tire speed) off the starting line.  As conditions become warmer (or as they deteriorate), the wheelie bars may be raised slightly, to compensate for the reduced traction available.  All three of these final adjustments are based on immediate track readings, as well as the performance of the cars that ran before them.

In the early years of the class, Pro Stock cars used an organic friction material (right), similar to what was used in street cars, though with beefed-up pressure plates. That’s the technology that was available at the time. Later, Pro Stock progressed to metallic friction discs (above) and later still, to carbon fiber materials before finally switching over to the sintered iron discs in the late ‘80s and early ‘90s.

Once a run is complete, crew chiefs then analyze and scrutinize the data from the onboard computer.  The crew chief will normally start by correcting the run to sea level conditions, in order to evaluate the performance, relative to previous passes giving the team a baseline to work from. The run will then be reviewed to evaluate the gearing, clutch pressures (base and centrifugal), chassis setup, and engine tune-up, along with the driver's performance.  Bringing all these elements together is what produces a winning performance.