a x b sizing, which is which?

[sparky33]

when a bike size is stated as A x B, is A the length of the top tube or the seat tube?
is the convention c-c or c-t?

could someone clarify this for me?

[NHAero]

Always have read "A" as the seat tube, "B" as the top tube

Originally Posted by sparky33

when a bike size is stated as A x B, is A the length of the top tube or the seat tube?
is the convention c-c or c-t?

could someone clarify this for me?

[jtbadge]

+1 to NHAero.

That said, there is zero consistency of the seat tube measurement being center -> center, center -> top of top tube, or center -> top of seat tube, so always clarify.

[sparky33]

Thank you!

[osbk67]

Stating frame measurements as AxB dates back to when horizontal top tubes were a given. In common usage among Italian builders in the 70s and 80s, and probably well before then, but that's well before my time.

Given the horizontal top tube, expressing an AxB frame size was "always" based on two centre-to-centre measurements. Anything other than that is probably a more recent corruption of what used to be a perfectly logical approach, brought about by sloping top tubes, and perhaps seat tube extensions.