Thanks. This is especially the "assume a tire width" that is a problem - are there hard rules for which width is possible for X (X being something I measure)
My problem is that I have a rim that is there for good, and then I would like to see which tires are possible for that given rim (there are several choices of width and I do not understand what drives the minimal and maximal width - I can imagine the the brakes are a limiting factor for the maximum width, but maybe this maximum is smaller because [some measurement of something]).
