seat post height?

songwriter

Is there a golden rule? Must your leg extend straight to the pedal with a parallel foot to the floor?

Smokin Joe

The knee should still have a bend in it when the pedal is at it's lowest point, you've run out of power by the time the leg is completely straight. There are plenty or articles on the net that deal with positioning, Sheldon brown is a site worth checking out.

dennisn

Sit on the bike with one foot clipped in. Put the heel of your other foot on the other
pedal. With that pedal all the way down at 6 oclock your leg should be almost fully
extended. Move the saddle up or down if it isn't. This will allow for the proper bend in your leg when you are clipped in. Smoken Joe is right on in saying that you don't want
your legs to be fully extended when you ride. There needs to be some knee bend at the bottom of the pedal stroke. Spinning is really hard if you have your legs fully extended
and to much bend at the bottom makes your thighs work harder than need be.

dennis Noward

feel

Hi songwriter if you are checking your seat height also worth checking its fore & aft position. When your feet are in the quarter past nine position they usually reckon the bone just below your knee cap on your front leg should be vertically above the spindle of that pedal. The easiest way to check is to get someone to take a digital photo of you on the bike.

Cajun

http://www.coloradocyclist.com/bikefit/
Saddle Height
With the right frame size, you'll be able to set your correct saddle height, which will be within a centimeter of .883 x inseam length, measured from the center of the bottom bracket to the low point of the top of your saddle. This allows full leg extension, with a slight bend in the leg at the bottom of the pedal stroke.

LeMond recommends that you then shorten this length by 3mm when using clipless pedals. Also, you might consider a slightly taller saddle height if you ride with your toes down and your heel raised. Most importantly, make any changes in saddle height gradually, and give your body time to adapt to the new position.

http://www.peterwhitecycles.com/fitting.htm

John.T

Get someone to ride behind you and check if your pelvis is rocking on the saddle. If so it is too high. The heel on the pedal method is a good starting point but it is only that. If you tend to ride toes down it will be too low, if heel down then maybe too high. Your saddle should be as high as you can ride comfortably with no pelvis rock. Too high or too low and you will loose power.
The knee over pedal spindle is also only a good starting point. We all ride and are built differently so no formula will work to find the 'best' position, only a starting point.

Mettan

Also keep an eye on your saddle height in relation to knee joint forces - too low and it'll substantially increase patella-femoral forces, too high and it'll add increased strain on your cruciate ligaments.