# Coefficient of drag and lift of a car

https://www.simscale.com/projects/sickman/car_with_spoiler/

I need some help with the coefficient of drag and lift in simscale.
How to set the values of drag and lift in forces and moments coefficients for a given design?
and is anything wrong with the simulation in the above link?

Tagging @yosukegb4, @Get_Barried as well as @Retsam and @DaleKramer here. Yosuke created a post regarding that a while ago, but maybe he can give you some tips specific to your project now.

Best,

Jousef

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Hi @sickman ,

I checked your model a bit.

• No boundary condition on the car surfaces - set them as no slip walls for sure
• “Center of rotation” is on the half of your car wheel base and it may be [ 0, ?, 0 ] in your coordinate system
• “Lift direction” is [ 0, 1, 0 ] in your coordinate system
• “Drag direction” is [ 0, 0, -1 ] in your coordinate system
• “Pitch axis” is [ 1, 0, 0 ] in your corrdinate sysytem
• “Reference length” is the wheelbase length of your car
• “Reference area value” is the frontal projection area of your car

Please check them again by yourself.

Best,
Yosuke

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Thanks for the help.
Now I got some clarity about" Lift and Drag direction" but about" Center of rotation" and “Pitch axis”, I’m still confused.
Can you explain what exactly Center of rotation and Pitch axis means in this simulation and on what basis should we assign the coordinates for both of them.

Hi @sickman !

The pitch axis is needed to calculate Clf and Clr. Clf and Clr are very important for a car aerodynamics.

I hope my post and the capture image in it help you. The post explains about the pitch axis settings and so on.
The coordinate system is different from yours, but the concept of setting is the same.