I know other people have had the same problem that I've had of the small wheels on the Viomi a9 Stick Vacuum wearing out see.
I thought I would post what I used to fix it.
I bought some 10mm O ring cord and just cut it to size with a Stanley knife, then pierced and drilled the centre hole. The more accurate your hole in terms of being in centre the smoother the wheels will be, but you can be a little off and still have it work.
Works out to be a cheap fix (the link above is for an Aussie seller, you can get it cheaper from China) given each metre length can probably make 20 wheels.
Thanks for the post. I wasn't even aware of this issue until i read this, i thought the lack of smooth movement is due to the stuck dirt thay needs cleaning