btw my 55cm kilo measures out like a 58cm frame so telling someone who is a certain size not to ride a bike that is X size is ridiculous without knowing that frame's dimensions in the first place. No rule of thumb to fit just some guidelines to follow but comfort is key, don't believe me? Look at professional riders and how their bikes differ from one to the next and one can assume that that group of people are in about the same fitness level as opposed to us all annonymous internet people who could range from super fit to jabba the hut types!