Wheel cleaner - soft. Specifically for wire wheels
Why "soft"? The weakness in a spoked wheel is the spoke in the wheel rim approach.
It is rarely dense, older wheels anyway. Moisture penetrates inside the rim and aggressive cleaning fluid now gnaw firmly on the metal.
Surprises show up later than at the next tire change or earlier when erupted by rusty spokes.
The gentle FIX40 method: Spray Metal Cleaner on the rotating brush to that point where no more water and shampoo are efficient.