Originally Posted by
Kontact
To address your statements in order:
That is not how bike frames are generally made. Many carbon frames clearly have different stay lengths and seat stay angles. Moreover, the vast majority of frames do have variable seat tube angles. I named the only two exceptions I'm aware of. So I'm unsure what you're talking about.
I'm 5'4" and 74 STA also locates the seat on the front of the rails to get reasonable set back. That was my point - few seem to benefit from steep seat angles. Some folks need even more relaxed than 73, but 73 is a good average angle across side ranges.
The formulas can't be perfect, but it is important to remember that while crank lengths vary, the center of rotation doesn't. It is the average of all pedal positions. Lowering your saddle to accommodate a long crank arm means that you have doubled the hip and knee bend at the top of the stroke. There is no data to suggest there is only one right way of setting a saddle height for varying crank lengths. And, foot length is only a factor if you pedal toe down or have feet dramatically out of proportion to leg length. Otherwise, foot length and angle are part of the formulas - since they were derived from observation of cyclists. And the saddle to crotch measure is not to your tailbone. It is a measure to the soft tissue adjacent to the hip joints, and that relationship to where you actually sit is contained in the formula. Most people do not have radical difference in the location of those two spots on the groin, so the formula is taking that into account.
Fitters who don't measure angles are still measuring angles - they're just doing it from long familiarity. I don't do it because I like to confirm that what I'm observing matches a metric and I'm not fooling myself, but I don't have a decade of experience.
I can certainly see why pat formulas don't sit well with anyone. But I do think that we should acknowledge where the formulas come from (observation), and that the point of bicycle geometry is to get people sitting more alike than different. My thought is that we get wrapped around the axle with rules of thumb and kind of forget that you can make things too bespoke. Saddle height formulas provide good starting points, and maybe such an approach would work with set back.
Interesting comments, unfortunately most of them are made to statements that I did not make. For instance, I did not say, "Fitters who don't measure angles are still measuring angles" ....I said, "
They did not measure a single thing on me...." meaning they did not care about static measurements like distance from tailbone to floor or length or arms, etc. Not a single static measurement.
WRT foot length, toe angle, and cleat mounting position, it most certainly matters at the top of the stroke although not as much at the bottom of the stroke. Like most fitters, you are wrong.
I'm glad you have a decade of experience.
You are 5'4''. When you get to be more like 6'4'', you might appreciate why 73 degree can be and is often a bad starting point. Pinarello and Trek for instance do understand that, they have more like 72 degrees on big bikes. That was my point. Obviously, some prefer to be more over the pedals and might have a shorter torso.
You are telling me the back half is different from size to size? Interesting. The STA is identical as are the chainstays on all three of these very popular bikes. Are you not aware how costly molds are or that using the same mold for the back half saves a lot of money? Or that manufacturers don't like to save money.
https://www.canyon.com/en-us/product...etry/?pid=2893
https://www.cervelo.com/en-US/bikes/s5
https://www.bmc-switzerland.com/intl...c-grey-23.html