[j-c-c]

To heck with metal, I'd go carbon fiber, .045", alum .060" there are no normal significant forces at play other than centrifugal, and for this diameter I am assuming at non race speeds, minor. Road bumps would be biggest uncontrolled force, but heck normal hub caps stay on, mostly. You could go lexan at .125" but you would constantly be cleaning them to remove inside brake dust and you would need to make sure they are vented for heat related needed airflow. Not sure though how well they would hold up on a 0-150-0? mph timed run if you left the car sitting still after stopping: eek:

PS, all my dim above are for a flat disc, and any shape would add stiffness and thickness could be reduced further.