I spoke to a tyres guy and he told me the pitch circle diameter for the Classic's wheels are 114. (FYI thats the distance between the bolt holes where the tyre is bolted at). Considering that, he recommened that the tyres I can use at max can be a 175/60 R14. Dunno if it can accomodate over 175, but that should be enough width. And 60 is appropriate height for a 14" Rim.