How does the 'Inerter' (J-Damper) work?

FIA banned the 'Inerter' (also called 'J-Damper') in 2022... but WHAT is that? And HOW does it work? 🤔

I will give you the answers in this thread... and explain how it could have mitigated porpoising!

Read on, and get ready to learn! 👇

Car suspensions have two components:

- Spring: applies a force proportional to its deflection➡️'Transfers' the energy of the bump to the car body.
- Damper: force proportional to HOW QUICKLY it deflects➡️Dissipates such energy.

F1 cars also had the Inerter... but what is it for?

The inerter applies a force proportional to the acceleration between its two extremities.

So:
- Suspension Deflection➡️Spring Force
- Deflection Speed➡️Damper Force
- Deflection Acceleration➡️Inerter Force

Invented in 2002 by a professor, F1 teams quickly adapted it to their needs!

A scheme:
When the suspension extends or compresses, the right ring moves relatively to the left ring ↔️

Due to the thread profile, this produces a rotation of the inertial body (in🟥red).

This produces an inertial force proportional to the acceleration between the two rings.

How is this useful?

For any oscillation:
Acceleration: - Deflection*Frequency^2

1) The higher the frequency, the higher the acceleration vs the deflection.
2) The acceleration has OPPOSITE sign compared to the deflection.

So the Inerter 'contrasts' the spring at high frequencies!

So, the Inerter effectively makes the suspension softer at higher frequencies!

This is the 'holy grail':
- Engineers can use a stiffer suspension➡️More stable aero, more responsive car ✅
- At higher frequency (kerbs/bumps), the suspension softens ➡️Less bouncing on unevenness! ✅

A practical example:

Vertical axis: tyre load oscillation (bad!)
Horizontal: frequency.

First, the engineer stiffens the suspension to improve the aero (solid to dashed line)➡️Problem: the peak increases.

Then, they employ the inerter (bold line)➡️The peak reduces significantly!

FIA banned the inerter in 2022, on the grounds of cost reduction. 🚫

The problem was that neither the FIA nor most teams predicted the porpoising.

The Inerter would have been the perfect weapon to fight it! (By having different stiffnesses at lower and higher frequencies).

So that was the Inerter! 🛠

Now you are one step closer to becoming an F1 engineer... or just a more tech-savvy fan!📚

Share the thread with your friends if you enjoyed it, and follow my page to understand Formula 1 better!🤩🏎

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If you’re a Motorsport fan, SimRacer, or engineering student, then you cannot miss this thread! 🔥

A fast car is useless if you cannot setup it correctly: curious about how we engineers tune its suspensions to reduce the laptime? 😏

Read on, and get quicker! 👇

Suspensions = springs (elical springs + antirollbars) + dampers + linkages.

They connect the chassis to the wheels, allowing a relative motion between the two.

They impact 3 main things:
1) Car's balance when cornering
2) Body movement
3) Unnevenness absorption

1) Car's balance when cornering

When cornering far from the grip limits, the car will move in the direction of its front wheels.

At higher lateral acceleration, instead, the car will start to lose grip:
- If it loses grip at the FRONT first, it will UNDERSTEER (point towards the OUTSIDE of the corner).
- If it loses grip at the REAR first, it will OVERSTEER (point towards the INSIDE of the corner).

We must avoid extreme behavior: we do so by transferring grip to the lower-grip axle.

...And guess how? Through the suspensions, of course!

Increase the spring or antiroll bar stiffness of the axle with more grip, OR decrease the stiffness (soften) of the axle with lower grip!

(The softer axis will gain grip at the expense of the other.)

Refer to my scheme:

While the springs/antiroll bar stiffness determines whether a car is understeering or oversteering when cornering, Dampers influence that behaviour on corner entry and exit.

The setup is analogous to the springs: refer to my scheme:

As you can see, the dampers have 4 fields each. The 'Fast' fields are relative to the response to road unevenness: it does not affect the car's balance.

Bump/Rebound (damping when the wheel is moving up/down) should go hand-in-hand, as should damping and suspension stiffness.

2) Body movement

- Softer springs: higher body roll (left/right rotation) and pitch (squatting/diving rotation).
- Softer dampers: the body movement lasts longer.

A race car should have stiff and dampened suspensions to be reactive, but not too much, or it will jump on bumps/curbs!

You can also exploit this to improve the aerodynamic performance!

Softer rear springs➡️The rear axle squats at high speed, under the effect of downforce➡️The angle of attack of the wings reduces: the car gets a better top speed!

Use this trick to overtake your friends.

3) Unnevenness absorption

Racetracks still have bumps, and you must go over the kerbs to minimise the laptime.

The more uneven the track (e.g. Nurburgring Nordschleife), the softer the springs must be, and especially reduce the fast damping of the shock absorbers!

'Ok, so... how do I start?'

1) Take a long corner,
2) Does it understeer a lot mid-corner?➡️Soften the front and/or stiffen the rear.
The opposite to solve oversteer.
3) Does it understeer a lot on entry/exit?➡️Reduce front damping and/or increase the rear
Opposite for oversteer.
4) If the body rolls/pitches too much➡️Increase the stiffness the same amount front and rear.
5) If the car is unstable on bumps/kerbs➡️Reduce the fast damping the same amount front and rear, and possibly the stiffness too.

That's it! Now you're on your road to become a racecar engineer... or at least a better SimRacer! 🔥

If you found the thread useful:
- tag a simracer friend✅
- follow @FDataAnalysis for more posts like this!✅

Let me know in the comment whether the explanation was clear!