Aero for the
iRacing FR2.0
Wings, Rake and Drive Train--The Data
Intro:
Being able to
go through corners at a high rate of speed is an important characteristic of a
race car. This is in addition to the car’s ability to accelerate and attain a
high terminal, top speed.
The cornering
speed is dependent on grip produced by all four tires. Grip is highly dependent
on the downward force of the tire against the pavement. Adding weight provides more grip, but comes
with the cost of higher inertia in the corners.
Since the additional grip from added downward force is not “linear”
meaning that it has diminishing returns, adding weight actually reduces
cornering speed.
But, with
aerodynamic downforce, there is no additional weight, just downward force
produced by air flow over the body and wings. Hence, significant grip is added
and significant higher cornering speeds is achieved. An added benefit is that
the added grip actually increases exponentially with speed. With aero downforce, more speed produces more
grip which allows more speed
.
Aero
downforce is a relatively new technology. Before the 1970’s, cornering g-forces
above 1.5 were impossible. Today, some really fast cars are generating
cornering g-forces at the 4.0 level. Here is a link for more background about
race car aero:
Now, let’s
focus on the iRacing FR2.0. There are essentially five (5) different
adjustments that will affect changes to aero downforce and drag: 1) Front Wing
Setting (14-31); 2) Rear Wing Setting (4-18), 3) Front Ride Height, 4) Left
Rear Ride Height; and 5) Right Rear Ride Height.
More wing
produces more downforce which provides more grip, but comes at the cost of more
aerodynamic drag which reduces acceleration and top speed. The process
of optimization is much more complex than the concept. Often the best
result is achieved only through a series of experiments or trial and error. And,
such experiments take less time if you know the generally expected cause and
effect from your changes, and if you have a reasonable starting point.
In addition
to wings, downforce is affected by ride height.
Ride height affects two types of downforces, ground effects at the
underside of the car and downforce from the incline or rake that it produces by
air pushing on the top of the car’s bodywork.
Both of these types are affected by the rake or the amount the rear is
higher than the front. Ground effects
become more important as the front ot the car is lowered, reducing the amount
of air that flows under the car from the front.
Testing:
Knowing the “best”
settings and more importantly the effects of various settings requires testing
and experimentation. So, let’s go to our “test track” that I use for testing
aero effects in iRacing. I take the FR2.0 to Talladega, the longest (2.66 mile/4.28 km) oval track available. We use telemetry to measure speed and ride height at the fastest flat section.
Here are the
initial settings “A”:
Front Spring (700#) Ride Height (0.658”)
Rear Springs (800#) Ride Height L/R (1.046)
Static Rake 1.046-0.658 = 0.388”
Rear End Standard 9/30
7th Gear High
Front Wing: 31 Max
Rear Wing: 18 Max
We will refer to this as Max Wing, Min
Rake
A Results
(Max Wing/Min Rake):
Top Speed of
152.1 mph (7300 RPM)
Dynamic Rake
at Top Speed 0.540-0.440 = 0.100”
Front Pushed
Down at Top Speed 0.218” (33%)
Rear Pushed
Down at Top Speed 0.506” (48%)
We then
changed the wing settings to minimum while keeping all else the same. This we
refer to as the “B” settings with Minimum Wing and Minimum Rake:
Front Spring (700#) Ride Height (0.658”)
Rear Springs (800#) Ride Height L/R (1.046)
Static Rake 1.046-0.658 = 0.388”
Rear End Standard 9/30
7th Gear High
Front Wing: 14 Min
Rear Wing: 4 Min
B Results
(Min Wing/Min Rake):
Top Speed of
157 mph (7500 RPM—Hit Rev Limiter)
Top Speed of
159 mph (7250 RPM—Rear End 10/30 with
Low 7th Gear)
Dynamic Rake
at Top Speed 0.660-0.560 = 0.100”
Front Pushed
Down at Top Speed 0.098” (15%)
Rear Pushed
Down at Top Speed 0.386” (.37%)
We then
changed the rear ride heights to increase Static Rake, while keeping all else
the same. This we refer to as “C” settings with Minimum Wing and Maximum Rake:
Front Spring (700#) Ride Height (0.660”)
Rear Springs (800#) Ride Height L/R (1.343)
Static Rake 1.343-0.660 = 0.683”
Rear End 10/30
7th Gear Low
Front Wing: 14 Min
Rear Wing: 4 Min
C Results
(Min Wing/Max Rake):
Top Speed of
158 mph
Dynamic Rake
at Top Speed 0.880-0.530 = 0.350”
Front Pushed
Down at Top Speed 0.130” (20%)
Rear Pushed
Down at Top Speed 0.463” (34%)
So the A, B
and C settings provide insight as to the effects of wing and rake settings over
the entire range, from minimum to maximum.
While it is theoretically possible that a rear wing setting higher than
15 might be beneficial, personal experience indicates that a settings of 31
Front and 15 Rear with the maximum rake would be considered HIGH DOWNFORCE.
So let’s test
that as “HDF” settings:
Front Spring (700#) Ride Height (0.660”)
Rear Springs (800#) Ride Height L/R (1.343)
Static Rake 1.343-0.660 = 0.683”
Rear End Standard 9/30
7th Gear High
Front Wing: 31 Max
Rear Wing: 15 (3 clicks below Max)
HDF Results
(Max HDF Wing/Max Rake):
Top Speed of
152.1 mph
Dynamic Rake
at Top Speed 0.820-0.400 = 0.420”
Front Pushed
Down at Top Speed 0.260” (39%)
Rear Pushed
Down at Top Speed 0.523” (39%)
Note 1: The
HDF setting with Low 7th and 9/30 Rear hit maximum speed of 149-150
at Rev Limiter RPM of 7500. Essentially the 9/30 Rear is used almost at every track, and the High 7th is used when top speed above 149 mph is desired and achievable.
Note 2: Changing the Front Spring in
the HDF settings to 800# resulted in a 0.2 mph faster speed of 152.3 mph, with
Dynamic Rake of 0.820-0.460= 0.360”
Next
we test changes in cornering force:
I
took the FR2.0 to the Centripedal Test Track--ran it on the band/lane, 4th in
from the outermost band/lane. Morning Default. Normal race settings, with 25/4
wing settings. (This is minimum rear with front set for a "balanced
setup" using tire wear/temp.) Max steady speed of 125mph. Increased to
31/11 wing. Max steady speed increased 3 mph to 128. (Tire pressure does matter
as I was 0.5 mph faster with 1 psi increase.)
Increasing downforce can result in higher cornering speeds of 3 mph, with a corresponding decrease in top speed of 3 to 5 mph IF speed above 150 mph with low downforce is achievable.
This is a lot of data to digest, so I will provide an additional article with more discussion in regards to how to apply this knowledge in Part 2.
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