I bought the biggest one 33 cms for my hamster ! It’s like comparing the size of the London eye to my hamster ! She loves it and runs like tha clappers on it. Very quiet, built well and great size. The cork is much thinner that I was expecting but it’s okay for my hammie.
I really love this wheel, its massive and makes my giant hamster look tiny. In a normal syrian sized wheel she is uncomfortable but in this (28cm) one she almost has a flat surface to run on.
The only problem is that the material inside the wheel is cork which is likely to be easily damaged and not easily cleaned. It's also more expensive than other wheels of the same size and I only chose this one for aesthetics.