Originally Posted by FarHorizon
The bike shop fit me to both bikes by measuring foot angle to the ground at full leg extension and knee over pedal spindle by a drop weight. Wouldn't the combo of these two measurements eliminate any differences in tube angles?
No.
Not if you have different length cranks, different pedals, different q factor, different seat post set back, different shoes, shoes with the cleats set differently, different orthotics in the shoes, lots padding in your shorts or not etc.etc. From year to year some saddles with the same name get changed, and the name remains the same.
Even if the seat tube angle is the same lots of things can throw off the way you sit on the seat, your leg angle can be more forward, backwards, or your legs can be open or closed more, changing how your sit bones hit the seat.
Using the identical saddle on a different bike may not work just because the saddle is the same.