Originally Posted by
Dean V
The whole point of a bike fit and its dimensions are based around the BB centre. The same as stack and reach numbers.
How the frame geometry allows you to achieve that fit within normal parameters of stem lengths, spacers, and saddle position on the post is why stack and reach numbers are the best for comparison.
The only down side is how stack affects reach numbers which has been pointed out in a previous post and easily compensated for by a simple calculation.
This assumes you are willing and able to, if need be, exchange the seat, seatpost, stem, crank and/or bar. Else, there is no guarantee two bikes with identical og very similar stack and reach will fit the same. All of them affect the final fit.
This basic premise is often neglected, sadly.