There are a number of factors that prevent you from going fast on the bike, but the two main characters are:
Frictional Drag- from the resistance between the air flow and the objects exposed to the air flow (their surface-area). The resistance is a function of the viscosity of the air which, although very low, is significant enough to slow you down.
Pressure Drag- from the eddying motions that are set up in the air behind the rider as they ride. This is also termed wake (similar to that behind a boat). This type of drag is a strong function of the cross-sectional area of the moving body (you).
The figure below is a good way of illustrating the two. The object on the left is mainly subject to frictional drag, that on the right, pressure drag.
There are a number of equations associated with fluid flow but probably the most important is Bernoulli’s equation:
Why is this equation so important? It relates the drag of a cyclist to his or her velocity. You’ve probably heard that aerodynamics become more important the faster you go and it’s all due to the V2 term – drag is proportional to the square of your velocity i.e. Cyclist going at 10mph V2 = 100 Cyclist going at 20mph V2 =400 i.e. 4 times more
As you go faster, your drag increases more so.
Below is a comparative list of the various modifications that you can make to your bike setup to improve drag – however, REMEMBER: The most aerodynamically inefficient part of cyclist is the rider themselves. About 80% of the drag of a cyclist comes from the rider – bike FIT therefore is paramount since it affects aerodynamics on the bike and in particular, the pressure drag.
