[Joe K]

Um. Too much stress? The weight of the car is the same. The speed around corners is the same. The engine torque, horsepower, and acceleration is the same.

Sidewalls of tires presents a very flimsy envelope. The air pressure is the same.

The tread area is radial, but that is a hoop suspended by sidewalls and air pressure.

Very much more likely age and service and possibly a defect or two left over from manufacturing has caused this. No radial about it.

The cracks can be repaired by welding. You may need to "straighten" the wheel afterwards as welding (more than likely) will introduce distortion into the wheel - at least check. If run out is more than 1/8" you may feel it in the wheel or ride. Wheels can be straightened if you have the tool to do it.

Might be easier to just find another pair of wheels, spin check for concentricity, blast & check for cracks and broken spokes, paint and keep driving.

Joe K