Well my chinchilla is very VERY fat. Although, he loves to run on his wheels. But they keep breaking! We have bought about more then 10 wheels at the price of 25$ . They keep breaking under his weight as it seems. Or they are just very cheep. We got a new wheel that is more expensive but he doesn't seem to enjoy it as much. Although it has stayed together I don't like it and he doesn't either. I need a new wheel brand I think..... What wheels do you use? What ones would you recommend?