The position of the saddle should be adjusted relative to the bottom bracket, not to the ground or handlebars. For example, if the reach to the handlebars is too far, it is better to get a shorter stem than to move the saddle forward of its ideal location. More accurately, saddle height should be adjusted relative to the position of the pedals as fitting different pedals or different length cranks would also mean the saddle needs to be re-adjusted. In practice, the distance from the top of the saddle to the center of the bottom bracket is used as the saddle height, e.g., setting up a new bicycle using measurements from another, as this is easier to measure. Other methods and calculations are used for determining seat height, such as LeMond's formula.
The saddle height should be set so that when pedaling, the legs have a slight bend even when the pedals are at their furthest distance. This means that if the saddle height is properly adjusted, on bikes with traditional geometry, the rider cannot place both feet flat on the ground when seated on the saddle. If they can, their saddle is too low, unless the bike is a recumbent or other crank-forward design.
The saddle should be nearly level, although the height of the handlebars and style of cycling will cause this to vary. In professional bicycle racing, UCI rules require that the saddle be within 3° of level.
Fore and aft
Conventional wisdom dictates that the saddle should be positioned so that when the crankarms are horizontal and the feet are on the pedals the head of fibula of the forward leg is approximately above the pedal spindle in a vertical line. However, several authors argue that there is no anatomical basis for this. Furthermore, the relative position of saddle and bottom bracket varies between road racing, track and triathlon bicycles.
The range of adjustment differs for each saddle, and the comparison of saddles for increased ranges of adjustment can be confusing owing to their different shapes. In comparing them, it is the range of adjustment of their comfort points that need considered, and because the matter is largely subjective, giving it proper attention is difficult to do. The range of fore-aft adjustment for double-rail saddles rarely exceeds an inch or so, but advertisers claim that i-beam saddle designs can give up to 200% more adjustment range than some of these.
When the fore-aft adjustment range of the saddle needs further extension than the clamp affords, it may be possible to add a saddle adjuster. One such adjuster mounts on the existing saddle clamp and allows up to 40mm of increase or decrease in the fore-aft position of the saddle. Another method for increasing the fore-aft adjustment is the swept-back seat post, where the seat post has a curve in it over the six inches or so before the saddle. Because of the gentle sweep of the tube, the top part of the seat-post cannot fit within the seat-tube, so this solution is useful only for high seat positions.