This has been asked multiple times in discord so I thought I would add the subject here. To add a collision inside a vehicle the parent component in the rigid settings compound has to be checked. Also in the child collision part compound child has to be activated. Like shywizard has commented these settings can be applied while exporting a model in the new exporter for blender 2.9 or you can add the following example to the par by editing the i3d via notepad. Refer to the compoundChild part below. After saving the i3d in notepad and opening it back up in ge the grayed out box will be check like in the image below.
```xml
<Scene>
<Shape shapeId="1" name="colPart01" translation="0.000757065 1.00552 -1.00853" compoundChild="true" collisionMask="8194" density="0.001" nodeId="166" materialIds="4" castsShadows="true" receiveShadows="true" nonRenderable="true"/>
</Scene>
```