It hasn't arrived yet Engel, but has been shipped, so hopefully in the next few days
I have the smaller 21cm version and it's a very easy wheel for getting in and out of as no edge to it - it can almost be at substrate level if needed. Would it be deep enough for rats though? There's also the round wood bit in the middle - could their tails get caught in that? I think it's just a decorative front to the ballbearings - when mine comes I'll check if there's a gap there.