Originally Posted by
PeteHski
One thing I would say relating to saddle height is that we should not automatically assume that shorter cranks require a higher saddle height. It all depends how optimum saddle height was determined in the first place. One experienced UK fitter suggests starting with the same saddle height when fitting shorter cranks.
Absolutely. I read the link you had posted to this approach.
The model doesn't say anything about what you
have to do, of course. The model is just a tool to think with, and one has to be very aware of its limitations: it shows the set of mathematically solvable solutions
that maintain a particular measurement (as I set it up, contact point to pedal axle). This is not necessarily the best or only measurement to start with, and as you say, there is nothing that says that this has to remain constant at all, but the model needs to start with something.
One could choose another measurement to start with, and that would be interesting. Back angle would be one thought... It is also possible in the model to unconstrain absolutely everything but body dimensions and the frame angle, but again, this won't tell you what you must do or that one solution is better than the other. It will just show you what is mathematically possible given your leg lengths and the seat tube angle. The model will even let you bend the knee the wrong way, if you really want to
But as I said in No 1. above, the one thing that really jumped out at me from the model is that it doesn't make too much sense to overthink this. There are so many variables, as well as the option of not changing anything but the crank length. And we aren't even getting into the front half of the bike yet! It makes the most sense to find a personal solution by riding.