Even within the relatively narrow (~56-59cm) range of frame sizes that I would consider making the effort to get fitted to, I firstly look at frame angles in terms of their effect on fit, both directly and indirectly.


Directly, because the seattube angle positions the entire length of the toptube fore and aft, though doesn't define the saddle's position by one whit. So seattube angle must be "weighed" against the toptube length for getting started with fit.


Indirectly, the headtube angle may affect what range of stem lengths will allow desired steering behavior with the rider in or out of the saddle, which are two very different things. Head angles of frames within my size range are usually paired with a compatible fork rake dimension that makes any handling changes due to stem length changes somewhat predictable. Among the very large number of builds that I have fitted myself to, generally a steeper headtube angle gets along well overall (while riding both in and out of the saddle) with longer stem lengths, while shallow headtube angles may require a cm's-shorter stem in order to handle safely while riding off of the saddle.


All of the above, though far from comprehensive, is sufficient for me to predict if a frame (within my familiar size range, or a little larger) will justify the effort of a build, in that it can be made to handle properly with a stem length that I expect to need to get fitted comfortably. I've literally been through the "full" range of headtube angles, multiple times, even at the extremes from 69-degrees up to 76.5 degrees, and no longer do I get stuck with something that I don't want to ride due to fit and handling considerations.
And given the range of diameters and styles of handlebar and steerer attachment over the past 60 years, you might guess what my handlebar stem inventory looks like!


In one recent case of a larger (59cm) 1979 Fuji professional with a 75-degree HT angle, the expected "twitchiness" of this bike with it's original 9cm stem surfaced initially, but with a change of tires/rims (from 22mm tubulars to 25mm clinchers), and installing a longer chain to allow moving the rear axle rearward, I quickly adjusted to the bike's still-lively feel and it soon became a favorite ride. The stock stem was unique and rare, so any change there would have compromised the bike's originality further, so I gave the rather short, catalog-spec 9cm Nitto "Crystem" (with narrow bars) a go, and was just able to make it work as Fuji intended.