To better understand the Ackermann steering, let's talk a bit about the wheel physics. A car
turns simply by tilting the front wheels. But it does not keep moving straight after the
wheels tilt. The answer lies in the physics of wheels. For a wheel to roll perfectly, its
contact point with the ground must have zero velocity to prevent slipping. This happens
because the wheel has two motions, rolling forward with the car and rotating around its
axis. At the bottom of the wheel, these motions cancel out, making the contact point
stationary. But what Happens if the car Keeps Moving Straight? If the wheels tilt but the car
keeps moving straight, the rotational and forward velocities no longer cancel each other
out, which causes skidding. To prevent this, the whole car must turn around a common
center point where all wheels align perfectly for rolling.
In simple terms, Ackermann steering makes sure the front wheels turn at different angles
during a corner. The inner wheel turns more sharply, while the outer wheel turns less. This
setup helps avoid tire scrubbing, when tires slide sideways instead of rolling. It allows both
wheels to follow their correct paths. This basic idea assumes that tires are always perfectly
aligned with the road. But in reality, tires operate with slip angles, a small angle difference
between where the tire points and where it actually travels. These slip angles are
necessary for generating grip and handling forces during a turn.
Slip angles vary based on tire load. The outside tire in a turn carries more load due to
weight shifting, so it needs a bigger slip angle to generate grip. The inside tire carries less
load and requires a smaller slip angle. This means that in racing, the ideal steering angles
don’t always match the simple Ackermann geometry. In Pro-Ackermann, the inside wheel
turns more sharply than standard Ackermann which is best for tight, low-speed corners for
autocross. It helps the car rotate better by creating more drag on the inside wheel, pulling
the car into the corner. In Anti-Ackermann the outside wheel turns more sharply which is
best for High-speed, sweeping corners for cars like Formula 1. It balances the slip angles
for maximum grip and stability, especially since less steering input is needed at high
speeds.
Nowadays there are different simulations software and libraries available. They can be
used in order to enhance the Ackermann geometry in following ways ---
- We can simulate different driving conditions such as high speed and low speed
conditions, tight cornering etc. and see how the set up works. If it fails to behave
accordingly, fine tuning the Ackermann geometry is needed.
- We can adjust the slip angles with these software. They are able to calculate and provide
the best slip angle for the tires. The right slip angle will ensure improved traction and
reduce tire wear.
Resources-https://youtu.be/oYMMdjbmQXc?si=ituAeOl67eCq5Gw9
https://youtu.be/O2ONv5MrpFg?si=fBIq1evs4Snivr9G
https://youtu.be/YVisLuiU-Oo?si=IuKhB-6DoT5Nj18
https://youtu.be/7d2K_mKgsZ0?si=FvOhuiIFdWVWU-Vk