arm length, trunk length, saddle to bar drop, bar choice, saddle choice, saddle layback.
Another factor with track frame that it tend to have a steep seat tube.
So a normal 54cm TT bicycle with a 75 degree seat tube*, now each degree add an extra cm to the top tube, so it's realistically 55cm TT.
76 degree mean TT is realistically 56cm, etc. you get the picture.
To be fair on Jack, he did get a frame that fit him a lots better than that Leader I remember him riding looking cannily like Graeme Obree on his superman position.
*this is if you set your saddle back as you would on a road bike for comfort.
Another factor with track frame that it tend to have a steep seat tube.
So a normal 54cm TT bicycle with a 75 degree seat tube*, now each degree add an extra cm to the top tube, so it's realistically 55cm TT.
76 degree mean TT is realistically 56cm, etc. you get the picture.
To be fair on Jack, he did get a frame that fit him a lots better than that Leader I remember him riding looking cannily like Graeme Obree on his superman position.
*this is if you set your saddle back as you would on a road bike for comfort.