frame size questions?
 

It measures 53 c-c, 54.5 c-t, with a generous 54.5 top tube. (off a keirin culture frame size)

were does the 53 come from?
I thought and I guess I thought wrong that the seat tube lenght was the size of the frame.
can some one please enlighten me?

Hopefully I've got this right but the 53, for these figures, is the measurement from the centre of the bottom bracket to the centre of the seat tube/top tube junction (hence c-c, centre to centre). The 54.5 is the measurement from the bottom bracket centre to the the top of the seat tube/top tube junction (hence c-t, centre to top). So both are measures of the seat-tube length.

Most off-the-shelf frames are 'square', where the top tube and seat tube are the same length, so it doesn't matter what is listed as the size. When the tube lengths differ, its a mixed bag whether folks list top or seat tube lengths.

Top tube length is a more prevelant measure of a frame's size. But you really need both top and seat tubes length to ensure a good fit.

[Edit: Damn Ceya knows his stuff, had no idea Keirin frames were listed by seat tube lengths]

It is 53 center to center , he is supposed to add 2cm and get 55 center to top. that is how they measure over in Japan. it comes out correct.

This applies only to the seat tube as top tubes are measure center to center.
S/F,
CEYA!