Originally Posted by
Kontact
Fitters don't use any simple metrics, and if you asked a fitter they would tell you that only a fitter can help you pick a frame size.
But I worked for a fitter for a long time, and height predicted frame size more reliably than inseam when compared to the frame size the fitter selected. So I'm not speaking of some sort of theory - I'm speaking as someone with decades of professional experience.
People with short inseams only have have standover height issues if they are trying to ride bikes with level top tubes. But sloping top tube bikes have drastically decreased standover for equivalent sizes. So what was true in the '90s isn't true today - a person with short legs can get what they need from a larger frame.
And that isn't just my opinion - many manufacturers, like Trek, offer height ranges along with frame sizes.
I simply don't understand why a person who's upper body goes with a 59cm TT and 11cm stem is going to ride a bike with a 54cm top tube without a ridiculously long 15cm stem. Tradition can't compete with basic math.
Your last sentence query as to why...portends to pros and better amateurs that deliberately size down for a shorter bike which results in a longer stem. You need not make your example so extreme to denigrate a smaller frame and longer stem commonly used in racing. A rider can size down 1 frame size to ride a bike that more matches their short inseam and use a longer stem to match their long torso. No need is the point to ride a bigger and heavier frame with short stem they may even struggle with to achieve an aggressive riding position with short inseam.