Is it ok use TYRE SIZE front 90/100/10 and back 90/90/10,Originally it came front and back is 90/100/10 SIZE
It's fine to use over or under sized tyres, although you should bare in mind that it WILL effect your handling. I put an over sized rear tyre on my old bike and it's turning circle was much larger afterwards. Also to note, the larger your tyres are the less effective they become if you ride on ice or slippery surfaces. I know this seems dumb but it's true :/
Usually the back has the bigger tire than the front. Very small bikes like yours may have both the same size. You are travelling at low speeds and it should be fine but it may look a little off.
