Hey everyone, welcome to Zebulon MSC's blog, where we will go over quite a
lot of topics related to motorsport, not just aerodynamics! For our initial post,
let’s start with Aero Balance, from the basics.

Aero balance is a term thrown around often but can be misunderstood. You
might hear someone talk about moving their aero balance forward or
backward, but what does that mean? Why is aero balance important?

First, we need to learn about the Center of Pressure. The center of pressure
(CP) is a fundamental concept in aerodynamics. It represents the point along
an airfoil or a body where the total aerodynamic force can be considered to
act. The figure below shows the center of pressure on an asymmetric airfoil.

From the center of pressure, the forces are broken up into two components;
lift (vertical component) and drag (horizontal component). This concept allows
us to simplify the multiple (often complex) aerodynamic forces acting on an
object into forces that we can compute and manipulate.

Lift and Downforce are used interchangeably – all wings generate lift. The
term downforce comes from the aerodynamic forces being generated in a
downward direction – good for sports cars, bad for airplanes. For the sake of
clarity, we’ll refer to lift as force upward and downforce as force downwards
for the next few paragraphs.

So where is the CP, what does it have to do with aero balance, and how is it
represented on a car? This balance is usually expressed as the percentage of
downforce on the front wheels compared to the overall downforce the car is
generating. While aero balance and the CP are related concepts, they differ in
that aero balance focuses only on the CP longitudinal position (front to back).
This means it only relates to the lift force (or downforce) generated by the
vehicle and how it is distributed. This position determines how much of the
overall downforce affects the front and rear wheels; a balance of the
aerodynamic forces!

What does aero balance look like in practice? Most factory road cars without
wings or spoilers will generate a small amount of positive lift as speed
increases. As you get into more performance-oriented cars, you start to see
wings, spoilers, front lips, and other aerodynamic devices. All of these devices
are being used to reduce the positive lift on the vehicle,
and potentially reverse the lifting force and start to push down on the car
instead.

It is important to consider aero balance because it can cause a car to behave
very differently at high speeds than it does at lower speeds. If a vehicle has a
100% aero balance (meaning all the aerodynamic downforce generated is
acting only on the front wheels) then the car would likely become very unstable at
high speeds. Of course, the opposite is also true: if you have a 0% aero
balance and only generate aerodynamic downforce on the rear axle, then your
car may become too stable and become very difficult to turn at high speeds.

OK, but how do we actually represent these forces?

Referring to the figure below, 'l' represents the car's wheelbase, 'a' represents
the distance from the CP to the front axle, and 'b' the distance from the CP to
the rear axle. Also, l = a + b. A longer 'a' means more downforce on the rear
wheels, while a longer 'b' means more downforce on the front wheels.
Depending on the magnitude of vertical aerodynamic forces (Fz), the ground
exerts reaction forces (Fzf and Fzr) on the front and rear wheels. Once you
know these quantities, calculating the balance is simple; 100 * Fzf / Fz, which
is the same basic ratio calculation used to compute your vehicle’s weight
balance.

So what is the perfect aero balance? How do you measure actual aero
balance? Turns out… it’s complicated. Stay tuned for how aero balance can be
used to tune the performance of a racecar, and why there are so many
misconceptions out there