Originally Posted by
DaveSSS
Effective top tube is irrelevant when using stack and reach. What is relevant is the seat tube angle. In rare instances, a frame might have an oddball STA that would require a seat post with zero setback or a lot of setback, like 32mm. In my size, a 74.5 degree STA is most common, but I sometimes see 74 or 75. 75 definitely requires a 32mm setback for me, but if the frame has a proprietary post with only 20mm, I'd pass.
Also remember that reach can only be compared at ONE stack height. ...
Geez, we have had this debate before:
Bike Forums - View Single Post - Retired and want to get back into cycling in my 60s.
1. With Reach, Stack, and Seat Tube Angle, one can calculate the Effective Top Tube.
2. With Reach, Stack, and Effective Top Tube, one can calculate the Seat Tube Angle.
It is just trigonometry. Thus, it makes no sense whatsoever to say that STA is relevant while ETT is not,
or vice versa. You are used to looking at STA, while I am used to looking at ETT.