Why Are the Formulas Not Accurate Enough?

Inseam Does Not Describe the Entire Leg

Two people may have identical leg lengths measured from the floor to the crotch, yet differ in the proportions of their femur and tibia, as well as in foot length. As a result, at the same saddle height they may have different knee angles and different foot positions.

This is the fundamental weakness of formulas based solely on inseam length. The literature indicates that anthropometric methods do not always produce the recommended knee-angle range because they fail to account for individual lower-limb proportions.

The LeMond Formula Ignores Crank Length

The LeMond formula determines the distance from the centre of the bottom bracket to the top of the saddle:

H=0.883×inseam

The problem is that the result does not take crank length into account. A cyclist using 165 mm cranks and another cyclist using 175 mm cranks do not cover the same distance between the saddle and the pedal axle, even if they have the same inseam and the same saddle-height measurement from the bottom bracket.

The formula may therefore provide a similar saddle height relative to the bottom bracket, but it does not necessarily produce the same leg-extension geometry.

The Hamley Formula Uses a Different Reference Point

The Hamley method uses the following relationship:

*H=1.09×inseam*

The result is measured from the pedal surface at its lowest position to the top of the saddle. Unlike the LeMond formula, it therefore takes the pedal position into account. However, it still assumes average body proportions and does not solve the problem of different pedal and shoe-stack heights.

In practice, the differences between the following are particularly important:

platform pedals,
SPD clipless pedals,
road pedals,
different cleat systems,
shoes with different sole thicknesses.

If the height of the foot above the pedal axle changes by several millimetres, the actual distance between the leg and the saddle also changes. Over many crank revolutions, this is not a negligible difference.

The Heel Method Is Only an Approximate Test

The heel method is quick and easy, but it mainly checks whether the cyclist can reach the lowest pedal with the leg fully extended. During normal riding, the pedal is pressed with the forefoot rather than the heel. This changes the ankle angle, knee position, and effective length of the limb.

The method is suitable for an initial bike setup, but it should not be presented as an accurate biomechanical measurement. Its result also depends on whether the cyclist keeps the pelvis stable and avoids compensating for excessive saddle height by rocking the hips.

The Knee-Angle Method Is Better, but Still Not Perfect

The Holmes method uses knee-angle measurement. A range of 25–35° of knee flexion at the bottom of the crank cycle is most commonly used. This approach is more closely related to the body’s actual geometry than a simple inseam formula, but it still has several limitations:

anatomical landmarks are difficult to identify accurately without experience;
the result depends on foot position;
static and dynamic measurements produce different results;
the angle changes with pedalling intensity;
the cyclist may compensate for saddle height through ankle or pelvic movement.

A review of the research indicates that a static knee angle of 25–35° may correspond to a different range during dynamic pedalling. For dynamic measurements, approximately 33–43° has been reported at low intensity and 30–40° at high intensity.

The Advantage of the Graphical Method

The main advantage of the graphical method is that it does not treat the cyclist and the bicycle as two separate, averaged objects. Instead, it attempts to represent the entire system, including:

leg length measured as inseam;
the femur-to-tibia ratio, which affects knee-flexion angles;
the position of the bottom-bracket centre;
crank length;
pedal thickness;
shoe height and the way the shoe connects to the pedal;
the actual saddle position, including its fore-aft position;
the geometric relationship between the saddle, pedal axle, and foot.

From this perspective, the difference between a platform pedal and an SPD pedal is not merely an equipment detail; it is a geometric parameter. A method that takes this parameter into account can help avoid errors that occur when a result calculated for one pedal-and-shoe system is applied to another bicycle.

For example, if a cyclist sets the saddle based on measurements taken with platform pedals and later switches to SPD pedals and shoes with a different sole height, the foot may be positioned higher or lower relative to the pedal axle. As a result, the knee angle will change even though the saddle height relative to the bottom bracket remains unchanged.

Comparison of Methods

Method1	Main principle	Key limitation
Heel method	The saddle is adjusted so that the leg is fully extended when the heel rests on the pedal	It does not accurately determine the position used with a normal foot position. People with unusually long or short feet may receive a significantly inaccurate result
LeMond	Saddle height = inseam × 0.883	It does not account for crank length, pedals, or shoe height
Hamley	Pedal-to-saddle distance = inseam × 1.09	It requires a specific measurement procedure and is still based on averaged body proportions
Holmes	The saddle is set according to knee angle, usually 25–35° of static knee flexion	The result depends on anatomical landmarks, foot position, and whether the measurement is static or dynamic. It does not account for differences in femur-to-tibia proportions or sex-related differences in leg proportions
Fizmoo graphical method	A graphical representation of the cyclist’s and bicycle’s dimensions, taking into account inseam and the pedal–shoe–crank system	It still requires accurate measurements and verification during riding