Thread by @Dalton_Kellett

Technical Thread: Dampers

An incomplete explanation of IndyCar’s most talked about setup item.

#INDYCAR #tech

Dampers on an @IndyCar serve to control the dynamic motions and loads of the sprung and unsprung masses (ie the chassis and the wheels).

Meaning, when the car is transitioning from one steady-state condition to another.

Example:
- Steady-State = going down the straightaway
- Dynamic = turning into a flat-out curve
- Steady-State = chassis settles into constant speed cornering

From turn-in to steady-state cornering. The chassis moves dynamically, the dampers affect this motion.

Damper v. Spring

Springs produce a force proportional to a displacement.

F = -kx

x = displacement (how much the spring has compressed)
k = stiffness of spring (units of lbs/in or N/cm).

The springs control the absolute amount of chassis movement under braking/cornering.

Let’s just consider body roll in a corner (no braking or heaving).

If a car corners at a constant 2G on a skid pad (2 x accel. of gravity), it will roll a certain amount. This total amount of body roll is only controlled by springs / anti roll bars.

But if we look at a real corner, the car will move from equilibrium to the set amount of roll. During that time, the dampers produce a force that is proportional to the speed of their displacement.

Important: the speed of damper displacement means the speed of the damper shaft relative to damper body. It does not mean the car’s speed!

Damping Force:

F(damper) = -c(dx/dt)

c = damping coefficient
dx/dt = speed of damper shaft

I’ve used an ‘=‘ sign but this relationship isn’t necessarily linear.

In that dynamic part of the corner, the damper has two jobs: Control the motion of the chassis and affect the contact patch loads of each tire (ie how hard the tire is pressing into the ground).

Controlling the motion:
generally speaking, the goal is to get through the dynamic portion quickly and without excessive motion.

When you turn the wheel you upset the system. Without a damper, the car would rock and oscillate. This would be uncomfortable and bad for the tires.

An undamped response would look like this

With a properly tuned set of dampers, the car will quickly settle into a steady-state.

More like this:

We only talked about body roll, in a corner with no braking. In reality, these principles applies in any way the chassis can move (roll, pitch, yaw, heave).

Contact patch loads:

(Or energy in/out of the unsprung mass, if you want to think more dynamically).

You can tune the relative damping force on the front and rear shocks to change when the front or the rear has more grip. (A subject that really deserves its own thread).

But in brief:
You affect the car’s handling by changing how much the front and rear dampers apply force in bump and rebound.
Bump = damper shaft going in (tire going up relative to chassis)
Rebound = damper shaft going out (tire dropping)

You can also tune how the tires/wheels (unsprung mass) respond to bumps and curbs.

For maximum grip, you want to reduce how much the bumps and undulations in the track cause changes in the contact patch loads.

^this is because tires don’t like variable loading. For more, ping @Cara_Adams.

Here’s a great clip by @murbanvideo showing the car hitting a bump (at Iowa), setting the chassis in a heaving/pitching motion, and recovering after a handful of oscillations. (Watch the rear wing/back of the car)

Dampers at work!

Dampers can produce force in high and low speed bump and rebound. So that’s 4 regimes.

Low speed bump and rebound. Generally 0-5 in/sec (damper shaft speed) and these mostly affect the handling of the car.

High speed bump and rebound (>5 in/sec) are mostly concerned with the bump / curb handling, track irregularities and undulations, and control of the unsprung mass.

So basically, dampers are really important because they affect the handling of the car in the dynamic phases of the corner, control how well the car takes bumps and curbs, and affect the amount of energy put into the tires.

This is a very sparse overview of the general idea of what dampers do.

Feel free to ask any questions!

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tiktok.com/@dalton_kellet…