I've been fitting riders on bikes for enough years to have a very clear understanding of the vexed issue of saddle positioning. Saddle positioning comprises 2 elements: Saddle height and saddle fore/aft. Both of these need to be addressed properly so we can avoid what is by far the most common cause of rider discomfort, injury and inefficiency.

Unfortunately there exists very little understanding in the broad cycling community and even worse, in the bike industry of how to establish saddle fit. This may sound presumptuous but I'm old enough and experienced enough in the bike fitting industry to be one of the very few qualified to understand when a rider has an optimal saddle positioning.

So lets dispel some myths about saddle fittting:
Optimal saddle fit is not a function of your leg length or some other measurement.
It is firstly determined by your discipline (Road, Track, TT, MTB, Trail, Downhill, BMX).
Next it is a function of your experience (recreational, competitive, elite, professional).
Then it is limited by your physiology (age, strength, flexibility, disability).
Lastly it is influenced by your pedaling dynamic (untrained, developing, mature).

So, let's be clear: Anyone purporting to want to set your saddle according to some measurement or another, be this leg length, seated knee angle, goniometer, plumb-bob - with or without the assistance of a Bike Fitting Computer Program - is ignorant and will likely only get close to your optimal saddle fit with the aid of luck. This is because we are ALL so different and idiosyncratic that 2 people with identical measurements in height, leg length, torso length, arm length, shoulder width and anything else are much more likely to have different bike setups than they are to have the same setup.

Much of what passes today as "Bike Fitting" is heuristic, legacy, legend, and derives from skewed perceptions of what rider commonalities we think we need to emulate. The first of these is that we think we need to LOOK like the professionals we see on TV in the big races. This kind-of makes sense though - clearly they are the best riders out there so if I can LOOK like him/her I can RIDE like him/her.

Well you aren't him/her and even if you were, that is no guarantee you have an optimal bike fitting, an element of which is saddle fit, and there are enough paid riders around with anything but decent bike fits.

Delving deeper: Saddle Height and fore-aft are interrelated elements of the saddle fitting. This is because on all bikes the seat tube and seat post are not vertical (90 degrees) but have a rearward slant that can vary from relatively steep (76 - 78 degrees on TT bikes) to more relaxed (72 - 74 degrees) on road and endurance road bikes. So clearly as you lower a saddle the more forward it moves relative to the bottom bracket and the higher a saddle, the more rearward.

And this leads to an important and often misunderstood fact: A rider's leg is not at it's maximum extension when the cranks are vertical, but rather when the cranks are parallel (in line) with the seat tube and seat post. This maximum extension is what we call Bottom Dead Centre (BDC).

So seat posts can be raised or lowered to adjust height, and all sadddles have rails that permit for fore/aft movement when clamping the saddle to the seat post.

These are all features that allow a coompetent fitter to put the rider into an optimal position. But the optimal position will always be determined by the individual rider.

For more, visit a competent fitter, one who doesn't want to use a computer and tape measure to set you up.