most sensitiv suspension paramter on setup/track testing?

[Ben A]

Hi,

I want to discuss what is the first the second and third and so on Suspension paramter you try to get in the ball park during setup the car for race track?

My suggestion is to have a good balance is more importend than to set a camber set to an accurat value :

Priority:
set ride height before:

1. Diagonal weigt less than 2kg dif.
2. weight on one axle side to side under 10kg dif.
3. good acurate toe setup
4. Camber diff. of 0,2° is ok? (i know to find a good camber we also messure the temperature, it is imported, but for a basic setup i mean)

Because all is an compromise! What is your suggestion about Steup, what is your way to get a well balacend car, what do you do first and second??

Thank you

Bean A.

[Edward M. Kasprzak]

Hi,

I want to discuss what is the first the second and third and so on Suspension paramter you try to get in the ball park during setup the car for race track?

My suggestion is to have a good balance is more importend than to set a camber set to an accurat value :

Priority:
set ride height before:

1. Diagonal weigt less than 2kg dif.
2. weight on one axle side to side under 10kg dif.
3. good acurate toe setup
4. Camber diff. of 0,2° is ok? (i know to find a good camber we also messure the temperature, it is imported, but for a basic setup i mean)

Because all is an compromise! What is your suggestion about Steup, what is your way to get a well balacend car, what do you do first and second??

Thank you

Bean A.


Thus starts a plan for a productive day of testing. I suggest developing a matrix of suspension settings which will allow you to determine the sensitivities to a given metric. Then you need to choose the metric (skidpad time, acceleration time, autoX time, "ease of driving"/subjective comments, telemetry channels, etc.) Eliminate as many uncontrolled variables as you can and take good notes. Don't forget to recheck your baseline setup occasionally to see how much your uncontrolled factors are affecting the results (your skidpad is rubbering in, your driver is learning and getting better, etc.).

And the data/results are the kind of thing design judges like me would be thrilled to see and discuss at competition.

Even the most believeable rules of thumb for what's important and what's not important are situation and design dependent. Others may make suggestions based on theory or their experience--and there's nothing wrong with that--but if you can drive the car I think you should do it. Use last year's car. You'll learn a lot for this year's design.

Once you know the relative size of each effect you can decide what to change first, second, third, .... Of course, some changes are more difficult than others, which also plays a role.

[Claude Rouelle]

Ben A,

You just asked a very wide (and wild) question. There are so many parameters on a race car (I am not even considering the driver) and so many parameters interconnections that there are no easy answers.

A few preliminary comments

1. If I was your faculty adviser (up to you to decide if is a good thing or not ) I would prevent you to go to the test track until you will have run a few simulations which qualify and quantify the influence that the main design and setup parameters will have on 4 essential steady state (or quasi steady state) car behavior characterization.
- Grip (can you reach the best possible lateral, longitudinal, combined grip that each of your tire has to offer?)
- Balance (do you have the right amount of yaw moment when you need it?)
- Control (Amount of Nm of yaw moment generated by each degree of steering wheel angle)
- Stability (Amount of Nm of anti-yaw moment generated by each degree of car CG slip angle)
Maybe later there are other factors like transient response quantification, ride etc.. (See the latest post or reply from Bill Cobb in this forum; a lot to learn there) but these 4 quantifications will be a good beginning.

2. You need to understand the design and setup parameters interconnection. Examples:
- What is the most important; 1 degree of camber or 1 degree of toe?
- If you change the spring should you tune your damper differently?
- If you change your camber should you also change the pressure? Sometimes you change the camber and the car is worse. You change the tire pressure and the car is worse. You change the tire pressure AND the camber your car is better. You need to figure out why.


That being said… if you want a short list, here is my very quick 10 “magic numbers” priority (but this priority list could be different with driver experience, racing category, track conditions etc…: WRC is not IndyCar which is not FSAE…)
1. Tire pressure. The easiest and cheapest way to gain performance and consistency. But much more difficult that it looks.
2. Tire temperature. The best tire temperature is the one ….. you had when you were winning.
3. Weight distribution. 0.2 % weight distribution difference could make a huge lap time difference. Yaw damping is a squared and b squared sensitive. a is distance between front wheels and CG, b CG to rear wheels axis
4. Suspended mass natural frequencies, roll and pitch stiffness (or gradient if you want).
5. Anti-roll stiffness distribution. That is a real magic number: when you have the right one and the lap time is good and the driver is happy and the tire are “happy” you may want to make a note of that number. If you are lost come back to it.
6. For car with wings, your front / total aerobalance
7. K2/ab. Essential for response.
8. You heave, roll and pitch damping ratio
9. Ackermann
10. Diff torque distribution in acceleration and braking

I should add the obvious brake balance but that is a driver stuff. If he can’t figure that out try another driver.

Remember; if you do not know WHY you win (or you make progress) you won’t know WHY you lose.

Hope this helps! Let us know.

[Ben A]

Hello,

thx for your answers.

@ Claude you give me a lot of things to think about and remember during the setup. Most of the stuff you said i now but it is great to hear the experience from a pro and the perception these pro think about the complex things.

We try to work with a good methodic to lose the try and error system from last year, you gave me us a good starting point.

Thank you