Frkl

I originally thought this too, but it's not a 1 to 1 relationship and shortening the crank does not necessarily or usually mean raising the saddle byll the same amount. Moving the saddle up also moves it back because the relevant measurement and point of reference is not directly down the seat tube with the crank aligned with it, but rather from contact point with the saddle (often but not always behind the seat post) to the pedal at the lowest part of the stroke (crank vertically down). So some of the difference is made up with horizontal movement of the saddle.

Hence the super scientistic slightly bent knee standard for seat post hight. This is to the lowest point of the pedal cycle.

The shallower the seat tube angle, the less up will be required to compensate for shorter cranks.

This also means that one could theoretically handle the entire change only by moving the saddle back, provided you have enough rails on your saddle. As a thought experiment, This can theoretically go on forever, and as you increase setback more and more, you must continually lower the saddle height. Eventually you end up with a recumbant, where (basically, this is a thought experiment), the entire saddle/pedal distance is accomplished through 100% horizontal setback and 0% rise. Changes in crank length on this recumbant will be entirely compensated with horizontal movement and 0 height change.

Futher reducing the up adjustment necessary when shortening cranks, and especially if the cranks are a lot shorter, pushing the saddle back may be necessary to keep the knee/pedal relationship the same. Unless you want a more triathlon like position, that is...

So seemingly paradoxically, the more you shorten the cranks, the less you need to move the saddle up because you need to move it back more to maintain the same knee/pedal relationship.