According to Gonzales and Hull this saddle set back position ranks third in
importance when it comes to efficiency. Just as with the crank length, the seat
angle is a factor that cannot be altered during the process of cycling. Because
the seat angle directly influences the efficiency, it is of vital importance to
determine the seat angle before purchasing the bicycle. The seat angle is the
angle that is made by the seat tube and an imaginary horizontal line. The most
striking example of an adapted seat angle is probably the so-called American
triathlon position. Here, the angle tends towards 90 degrees, whereas a
standard frame angle measures 72 to 75 degrees. The triathletes claim that for
them this position is more comfortable. They can ride their bicycles more
efficiently, they can exercise more power, and the shift from cycling to
running proceeds more naturally; however, solid evidence for these assertions
has not yet been provided. What is also striking is that cyclists assume
different positions on their saddles when riding different tracks. When riding
downhill, they tend to shift towards the back of the saddle, whereas during
climbing they move somewhat forward on their saddle. This might lead to the
conclusion that changing positions on the saddle has a mechanical or
metabolical advantage.
How to determine the optimal seat angle? When the saddle is adjusted at the
correct height and pedal and crank are positioned horizontally, the
perpendicular line should go from the knee cap straight through the pedal axle.
Research shows that there is increased stability of the saddle position when
this perpendicular is appr. 2 cm behind the knee cap.
Determining the seat angle by only measuring the upper leg-length does not
suffice. It should be noted that measuring of the seat angle should be
conducted while the cyclist is positioned on the bicycle. The sitting position
on the saddle is strictly individual, as it is influenced by the width of the
pelvis and the shape of the saddle. The position on the saddle determines the
position of the knee during the cycling movement; thus, the position on the
saddle influences the seat angle.
The standard-seat angle-geometry, at which large frames are equipped with a
shallow seat angle (72 degrees) and small frames are equipped with a shallow
seat angle (75 degrees), presupposes that people with longer legs automatically
have relatively longer upper legs than persons with shorter legs. The following
diagrams illustrate that this presupposition is incorrect. Diagram 1
illustrates the relation between total leg length and upper leg length with
students of the Technical University of Delft (Molenhoek, 1994). These
statistics clearly show that there is no difference in the relation total leg
length / upper leg length between people with longer legs and people with
shorter legs.
| 265 male students |
P5 |
% |
P95 |
% |
| Total leg length |
101.2 |
100 |
118,4 |
100 |
| Upper leg length |
58.6 |
57,91 |
67,8 |
57,26 |
|
89 female students |
P5 |
% |
P95 |
% |
| Total leg length |
95.8 |
100 |
111 |
100 |
| Upper leg length |
56.1 |
58,6 |
65 |
58,6 |
Diagram 2 shows the seat angle measuring results of 1028 persons according to
the bikefitting.com measuring system. In this group there were 39 males with an
inner leg length of less than 800 millimeters and 39 with an inner leg length
exceeding 960 millimeters. Also included in this group were 4 females with an
inner leg length of less than 700 millimeters and 6 with an inner leg length
exceeding 860 millimeters. Generally speaking, this correlates with categories
p5 and p95 of diagram 1.
| 974 male cyclists |
39 < 800 |
38 > 960 |
| Average seat own bicycle |
74.9 |
73.8 |
| Average optimal seat angle |
73.6 |
73.5 |
|
65 female cyclists |
4 < 700 |
6 > 860 |
| Average seat own bicycle |
74.6 |
73.5 |
| Average optimal seat angle |
73.5 |
73.5 |
Diagram 3 shows the standard seat angle for different frame sizes of four frame
constructors who (still?) take the incorrect supposition as described above as
their starting point.
| FrameSize |
Colnago |
Merckx |
Pinarello |
Cannondale |
Average |
| 48 |
75.5 |
76.3 |
74.5 |
75.0 |
75.3 |
| 50 |
75.2 |
76.6 |
74.5 |
74.5 |
75.2 |
| 52 |
74.4 |
75.0 |
74.0 |
74.0 |
74.4 |
| 54 |
74.3 |
74.4 |
73.8 |
74.0 |
74.1 |
| 56 |
73.6 |
74.0 |
73.5 |
73.5 |
73.7 |
| 58 |
73.5 |
73.5 |
73.0 |
73.5 |
73.4 |
| 60 |
73.2 |
73.2 |
73.0 |
73.5 |
73.1 |
| 62 |
73.4 |
72.8 |
73.0 |
73.0 |
73.1 |