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# If I judge you one day

by | Jun 6, 2024

## If I judge you one day

Some advice to be ready when you will face a vehicle dynamics design judge. This is the way I proceed…

BY CLAUDE ROUELLE

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### Then, and only then, if you succeed in answering most of these questions, I will let you speak....

If I judge you, I will start with these first steps (that is my logical order, but other judges could have a different approach).

1. The super basic questions. If you can’t answer these questions, you won’t go very far with me because:

• you will prove to me that you did not do the indispensable research
• whatever choices you made on your car design they won’t be justified
• you will prove you have no or little idea what you are speaking about
• and you started building a home by working on the roof instead of on the foundations.

Examples:

• You have understeer, do you move the weight distribution forward or backward?
• You have understeer, all other things being equal, do you increase or decrease your front track?
• If in the garage at 0 Km/h you turn the steering wheel to the left what is happening to the RF load; increase, decrease, or stay the same? Did you measure that? Why is it important to know the qualitative and quantitative answers to that question?
• What are your car’s yaw rate and the yaw moment on the skip pad?
• If it rains, do you move the brake balance forward or backward?
• What are the three causes of slip angle?
• Why don’t we have rear-wheel steering (I did not say all-wheel steering I so say only rear-wheel steering) on a race car (compared to a forklift for example)
• What is the altitude (z coordinate) of your aero center of pressure? There is a trap here…
• During a circuit lap, does your damper spend more time at low or high speed? Do not focus on the number but on the distribution of these speeds.
• Give me an idea of your tire and brake pad coefficient of friction window
• Give me the top five factors in a car design that will influence the car’s performance. How do you know that? Some of the factors are obvious, and some are debatable, I concede.
• You know where the kinematics roll and pitch centers are. Do you know where the yaw center is?
• If you have oversteer do you see more or less lateral acceleration on a rear lateral accelerometer compared to the front one?
• Define balance, control, and stability, and tell me in which units you measure them.
• You have an oversteer car on entry and an understeer car at the apex, what do you change on the car to solve both problems.
• Why should the rear roll center be higher than the front?
• What is critical damping? I do not expect you to give the formula by heart by you to tell me what the meaningfulness and usefulness of critical damping are.
• Does yaw velocity damping increase or decrease with speed?
• And a few other Vehicle Dynamics 101 questions like these.

I will shoot these questions with a machine gun. I expect you to start answering each of them before I have finished the question. And of course, I will not let you open any notebook or binder to be able to answer them.

Again if you can answer these questions you have tried to redefine Darwin’s laws (forms are defined by the functions, not the other way around) and you focused on car design forms instead of taking the time to understand how a car works.

After 5 minutes of your answer to these basic questions, I will have a pretty good idea of whether you master the fundamentals or not.

Then, and only then, if you succeed in answering most of these questions, I will let you speak….

## Tell me... (here we go)

2. The big picture: What were the main goals you tried to achieve in your suspension design, why did you choose these goals (answers could be very different from one team to another; budget, experience, available tools….), and did you achieve them (or not and in that case why) and can you demonstrate that you achieve them (test data validating the rightness of your suspension design choices)?

3. How and why did you choose the tires that are on the car?

4. How did you choose your weight distribution?

5. Explain your K&C (Kinematics and compliance) design choices (Camber variation in heave, roll and steering, Spring and ARB motion ratio, roll and pitch centers initial position and movement), Ackerman, steering effort, and compromise between weight and compliance. etc…)

6. How did you choose your spring, ARB stiffnesses, and your dampers rate?

7. Show me your aeromaps studies. Downforce, drag, downforce distribution Vs front and rear ride height, and ideally, yaw, roll, and steering. How sure are you that these maps are real and not pure academic studies? (I expect validation here). How did you use these aeromaps?

8. Show me your vehicle dynamics simulation. What did you simulate and why? Inputs, outputs, conclusions, and of course on track – validation.

9. Show me your test report and explain what you learned from it

10. Explain to me how your team is organized (who does what when), what is your team workforce, and your budget, and show me of you practically organize knowledge transfer from one year to another, year after year.

For all these steps I expect both simulation and validation data (in lab and on-track testing).

It is fine if you made the not so good initial design choice providing you understood and explain why and you can show what you did to correct it.

I will very quickly sense if you master your knowledge or not. Depending the answers you give, the documents you show and what I see on that car I could accelerate (I know you know so let me ask you more difficult questions – that is a good sign) or I can slow down (are you sure about this; can you elaborate – and that is usually not a good sign)

Hope this helps.

CLAUDE ROUELLE

FS & FSAE design judge in Australia, Austria, Brazil, Canada, China, Germany, Italy, India, Japan, Spain, USA.

Judge in more than 148 competitions!

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