Hi rhc! I had a look into your geometry and it seems like the geometry is not a closed volume. I've had that problem too with chassis. The best option to simulate it is using shell elements on the mid surface but SimScale does not support it yet. So one way to solve it would be editing the geometry in a CAD software (like Onshape) to make sure that all the tubes make a closed volume and meshing it with second order elements considering the small thickness of the tubes. If your chassis is simmetric you can use simmetry and save simulation time and cost. Something simmilar (in terms of simmetry) was made here https://www.simscale.com/projects/kcontractor/bikeframe_homework_1/. Cheers!