Originally Posted by
Dean V
That is the whole point of stack and reach. It is not affected by frame angles.
But they affect how your body interacts with those numbers. Different seat tube angles will put your body in different places in relation to the crank, and you may not be able to make up for that with saddle setback.
For instance, the reach on my two bikes are exactly the same, and the seat tube angle differs by only 0.5°
Yet, I have to have the seat slammed all the way forwards on one, and all the way backwards on the other (both 25mm offset posts), in order to give me the same fit. Same can be true with HT angle, only less drastically due to the short distance.