iRacing Dallara DW12 Aerodynamic Research

I tested the car at Talladega Speedway in order to test at the highest speed possible. Telemetry was used to determine dynamic ride heights.

(On this oval track, Diffuser settings are limited by iRacing to Sidewalls and Strakes both OFF.  On medium length speedways, iRacing allows Sidewalls ON, Strakes OFF and on some shorter tracks they allow Sidewalls and Strakes both ON.)

Front and rear wings were set at their minimum settings.  The results of many laps found that the optimum “least drag=most speed” was produced with “dynamic” ride heights of 1.000” front and 1.350” rear when traveling 233-234 mph on a  straight section of the track. This was counter to “rules of thumb” promoted by others indicating that a “nose up” attitude produced less downforce and drag.  

At speeds of 233-234 mph, the downforce with these ride heights produced having the lowest wing settings allowed (-4.5/-10.5) was:  Front: 420#; Rear 1200# as determined by spring deflection using 1:1 motion ratio. (Note: An exact motion ratio of ride height change to spring deflection is not available from public information so actual downforce figures should be considered to be approximate. It is assumed in this discussion that the ratio is different in the front vs the rear so downforce figures for the front are doubled.) Front: 840#; Rear 1200# as determined by estimated spring deflection using “estimated” motion ratio.

Initial “Static” ride height would be depending on the springs chosen.  For example: (2) 2800# front springs would compress 0.075” inches each (420x2=840# front downforce) so static ride height in the example above is 1.075” static front ride height;  (2) 1500# rear springs would compress 0.40” (1200# rear downforce) so static ride height in the example above would be 1.750”.

Spring rate choice affects handling, depending on track bumps and the transition from banked turns and less banked straights. (For example, the car at Talladega became very difficult to drive with rear springs stronger than 1500# as the transition from banked turn to straightaway creates a loose condition.) In general, from an strictly aerodynamic standpoint on ovals, the stiffer the better as the ideal "aerodynamic attitude" is maintained.

The next test was to learn how lowering the ride height would affect drag.  The car was lowered enough that it almost bottomed on the right side in the corner banking but the 0.35” front to rear “dynamic” rake was maintained on the straights.  Dynamic ride heights were 0.700” front and 1.050” rear.  Speed  and lap time dropped off approximately 2%.  

At speeds of 229-230 mph, the downforce with these ride heights produced while still having the lowest wing settings allowed (-4.5/-10.5) was:  Front 1000#; Rear 1500#.  Conclusion, lowering ride height will increase downforce AND drag. 

Another test was made that produced a dynamic ride height of 0.500” front and 0.850” rear. Here the car bottomed out in the corners, but still a downforce calculation was made on the straights:  Front 1600#; Rear 1600#.  Conclusion, lowering dynamic front ride height to 0.500” dramatically increases front downforce. The iRacing front to rear downforce calculator does not show this.  (This has important implications for the DW12 on road course, however there, the third spring must be taken into account.)

The Diffuser Wicker  created a very slight increase in drag and 25# rear downforce.  It is recommended that in most cases—set this diffuser at ¾” Sealed as its use will allow a very slight decrease in rear wing.

Each “click” of the front wing increased front downforce by approximatley 20#, e.g. 6 clicks produced a change of 120#.  Each click of the rear wing increased rear downforce by approximately  6.5#, e.g.  18 clicks produced a change of 120#.  The ratio of #/click front to rear was not linear. The higher the wing settings, the more the rear wing changes per click in proportion to the front. So on low wing settings, the ratio might be 4 clicks rear for each one click front, but at higher wing settings, the ratio is closer to 2 or 3 clicks rear for each click front.  (These ratios are affected by wing wicker settings.)

On tracks where turning “grip” is relatively more important than maximum straight line speed, downforce is improved by lowering the car, front and rear to the lowest possible dynamic ride height with minimum bottoming.  Maximum use of the diffuser or “wing under the car” also produced the best results—maximum wicker and maximum sidewall/strakes available.  This usually requires stiffer rear springs and often results in front and rear dynamic ride heights being equal.  (It is suspected that the “faster with nose up” rule of thumb is related to reducing rear ride height to lower the car—this does not increase top speed, but does increase downforce and speed through the corner, and therefore may increase speeds on the straights.)

Keep in mind that there are many, many variables that affect handling and speed. Finding the perfect setup for best lap times still takes experimental trial and error testing.  The knowledge above only serves to help us "zero in" faster on the best result.


Donald Wayne Strout 10/28/2015