I tried some 19inch o.z.'s with a larger than stock tires on my new f430. When I drove for a few minutes a cst error and buzzer went off. I put the factory wheels back on and no more error. Any answers for me?

 

I'm no expert but can it be your tire pressure monitoring system?
did your new wheels have those sensors?

 

i dont know what cst is but it's obviously telling you that it doesnt like the taller diameter - i assume that can mess up your e-diff.

 

CST is traction control, what size tires are you running? Tires can be wider but the overall diameter should stay within a parameter

Not having TPM Sensors will not cause that warning to come on, just a flashing sensor light.