Aero Features
Aerodynamics: a brief introduction
Every cyclist has to overcome the resistance offered by the air, or drag. Drag increases with the square of velocity and from about 20 km/h exceeds all other forms of road resistance combined (e.g. roll resistance, mechanical friction losses).
Drag:
FDrag = drag, in Newton;
cd (cx) = drag coefficient
A = frontal area of the body, in m2
Rho = air density, in kg/m3;
v = velocity, in m/s.
V = The velocity is variable and should be as high as possible.
Rho = The air density cannot be influenced; it is a given factor.
Drag can thus only be reduced by cd and A.
cd value:
The cd value describes the aerodynamic performance of bodies (c = constant, d = drag). Turbulence in the air occurs at those points where the airflow is interrupted disadvantageously. The air can then only flow past more slowly. The object becomes less aerodynamic.
The aim must be to control airflows by means of certain shapes so that a fast airflow is achieved and turbulence is minimized. In sporty riding positions, the position of the head and body decisively affects the cd value.
A frontal area:
The frontal area is the largest possible cross-sectional area of a body moving through the air.
Drag increases in direct proportion to the frontal area.
cd and A are dependent on the bike's aerodynamic shape and the rider's seated position.
The optimum balance between best aerodynamics and minimum power loss has to be achieved, especially when cycling over the 180 km distance of an Ironman race. The seated position is therefore the overriding factor that decisively affects all the influencing factors in the equation. In addition to the smallest surface of the bike, how finely a bike can be tuned to the rider is therefore of decisive importance.
The BMC Concept
Over the last 3 years our team of engineers has collected a lot of measurement data from athletes who use a time trials bike and has analyzed the data closely.
1. Analysis
The first clear differentiation can be found between triathletes and a pro tour team: while riders such as Cadel Evans have to deliver the maximum speed over a relatively short distance, so that the aerodynamic seated position and maximum power output are optimized, the strategy for triathletes is rather more complex. The Ironman athlete must find the most efficient solution for 180 km. The most efficient seated position in this case is the ideal compromise between the best power transmission with the least possible fatigue and cramping. Whereas Cadel only has to be lifted from the bike on reaching the destination, Andreas or Michael Raelert still have 42.2 km to run. This means that the muscles must be stressed differently.
The longer the distance that has to be covered with a time trials bike, the more important comfort is. For the traditional time trialist, comfort is much less important than it is for long-distance triathletes.
Extreme time trialists like Cadel Evans work for years on developing an ideal riding position for time trials. Every single mm of extra aerodynamics on the way to achieving the most aerodynamic position is painstakingly won. Once this position has been reached, there can be no compromises. The bike must allow this position. Triathletes, though, are different. They adjust the handlebar, the stem and the seatpost over the course of the season. And they keep doing so until they have found their ideal position.
2. Dynamic measurement - the adjustment
Athletes such as Andreas and Michael Raelert are measured up precisely by specialists in order to exhaust every last bit of optimization potential.
Minimal deviations or unevenness in the movements on the bike can be registered by microsensors that allow the precise movements to be calculated and projected in a virtual 3D space. The data are logged both to supply valuable database information for the development of the TM01 project and to enable the athletes to analyze their optimization potential in detail and utilize it to the full.
It is absolutely critical that this measurement is performed dynamically. Experts like Dr. Max Testa of the BMC Racing Team analyze the positions and the power achieved in watts. Physical dimensions alone do not determine the optimum - the individual muscular system and mobility of each and every athlete also play a part. This can lead to different results even if the body size is the same.
Once the seated position has been determined, it must also be possible to achieve this on the time trials bike. That is why the ease with which the position of the driver can be adjusted is the key to fast riding.
Vmax = p2p x subA
The biggest step in the development of the TM01 project, though, is at the next stage in frame development: adjustability after determining the frame size for the rider.
The requirement is to achieve
- the best possible aerodynamics
- with the most efficient seated position (having regard to comfort and performance)
BMC has turned this into a formula that allows ideal fine-tuning:
- V max is the goal: maximum velocity
- p2p stands for "position to perform"
- subA: The aerodynamics of the rider and the bike
The three elements of the formula V max, p2p and subA are explained below.
p2p - position to perform
The best "position to perform" derives from the maximum adjustability using the stem, the handlebar and the saddle position.
Tri Angle Concept
The Tri Angle Concept allows the stem to be adjusted in 30 different ways.
The principle is as simple as it is brilliant: the variable arrangement of triangular forms and spacers allows both positive and negative degrees to be achieved at any required length of the stem. This option is available ex works and is supplied with every TM01.
The variability enables the rider to set his ideal position. It also allows him to refine and modify the ideal seated position further in the course of the season's preparations without any great effort. All that needs to be done is add, replace or remove tri angle modules.
21_21 offset
The p2p concept is supplemented by a further feature that enables the saddle position to be adjusted to extreme requirements: 21 mm forward and 21 mm back.
This allows BMC both to comply with UCI regulations and to cover the extreme seated positions for triathlons. The reach of the saddlebar permits four different basic settings, while the whole reach of the bar can also be used to ride extreme positions.
