Originally Posted by jp_nyc
OK, now I'm confused. If a greater seat tube angle means a slacker geometry with the seat further back from the bb, why is it that when you push your seat back, you get a smaller angle?
Maybe it'll be easier for my brain to wrap itself around this if you can tell me how seat tube and head tube angles are measured (which angle, exactly, are we talking about?). Sorry for the basic q, but I guess it's about time I know this.
Thanks.
No I think you were right the first time. My custom bikes phisical seat tube angle is 71º, if it was exactly vertical it would be 90º and as it tilts BACK the numbers get smaller and the angle slacker in cycle speak. Anyway I have some setback AS WELL as the slack seat tube angle to begin with so the EFFECTIVE angle is even slacker at 69º.
Actualy it gets more complicated. Just about EVERYONE out there has an effective seat tube angle thats slacker than the frame geometry suggests. If you want to be precise you measure the angle from the centre of the bottom bracket to the midway point on the seat rails but even this can be a bit airy fairy due to differences in seat tube rails and seats in gereral. Even the concept of seat setback (nose of saddle to vertical line from bottombracket) can be upset by variances in seat design. IE how long the seat is and whereabouts on the saddle your weight centres.
Does that make any sense or is it getting more complicated.
Regards, Anthony