Good news - Rimowa 4-wheel spinner more spacious than 2-wheel!
I was just looking at the latest Rimowa catalog.
The two-wheel "IATA cabin trolly 2-wheel" (55x40x20) gives you 33 liters of space, but the same size 4-wheel gives you 35 liters.
So the four-wheel models actually give you more packing space. I don't think we knew that here(??)