Originally Posted by
rpenmanparker
As shown by the first quotation above, I never said that stack and reach describe fit. I said they invariably DETERMINE fit. That is a truth that you should know better than to dispute. And one which is hardly confusing. One need not refer to them when trying on a bike, but they are nevertheless the underlying factors in determining fit. They are there whether you choose to refer to them or not. In the complete bike stack and reach are modified by saddle position, crank length, stem length and angle, steerer spacers and such, but the stack and reach are the fundamental determinants of fit. Stack and reach are to the frame what the relationship of the three contact points is to the complete bike.
Fit is determined by where the rider wants the bars and seat to be. Stack and reach just tell you what it's going to take to get the bars in position.
In other words, fit is a mutable result, depending on rider desires. The same stack & reach measurements can accommodate a variety of fits.
I just don't see any useful cause to say that S&R determine anything, because except at the limits-- the point at which a frame just doesn't work and cannot be made to fit the rider and/or their needs either physically or in terms of performance and handling-- there are ranges of adjustment at the component level to get the rider in desired position.
Fit is not a set of points fixed in space, it still would not be determined by the frame, but by the rider.