Considerations about pressure in bicycle tires

When I searched for solutions to the optimal pressure, faced with the fact that about pressure itself it a lot of misunderstandings in the Net. Here I shall not describe it, but just give minimum of information and some practical conclusions.

Air pressure (P) in a enclosed volume (V) is described by the formula:

P * V = const = koeff * N, where N – quantity of the air, roughly speaking – the number of strokes of the pump, or the mass (weight) of the compressed air in the tire.
Approximately the same dependence on the width of the tire pressure (i.e., volume) for the same load on wheel shows the calculator of optimum pressure. That is, it can be assumed that the weight of a “man + bike” determines the required amount of compressed air for damping. Therefore, the greater the volume (tire width), the less pressure should be. No reason in terms of the damping to inflate wide tires as well as narrow.

When the wheel load or when the wheel drive over irregularities
– the volume of tire does not change, because the tire, though made from rubber, does not stretch because it reinforced. Tire changes shape, at the point of contact sags vertically but swells wide. Therefore, the pressure is also not changed. From this it follows that the total dampening properties on a good road do not depend on the width of the tire. That is, in a good road it about equally on comfort to rideon a wide and a narrow tire (if they are properly inflated). There are differences in the contact area with the road, in the narrow tires – less in general – more. But how it is important – difficult to say, because the friction plays to plus and to minus. Roughly speaking, the front wheel brakes while the rear, on the contrary pushing.

So, what is the key differences between the narrow and wide tires? It is necessary to note two points:

1. The narrow tire more light. For a good road it is important, since the general amortization is approximately the same.

2. In wide tire the pressure is less. It is here that I want to remember the definition of pressure: the force per area. This force is felt well if your press the tire by fingers. The lower the pressure, the more easily push fingers. In similar way, the tire interacts with the irregularities of the road: the lower the pressure, if the other conditions being equal, the bigger irregularities tire can take over and do not transfer to suspension. But it also depends on the elasticity of the side walls – on how easy the tire changes shape. If the side wall is thin, the narrower tire could be as soft as wide one, and besides, even more light (see. again n. 1). But it is less durable. Therefore, the comparison of softness with different widths works only for one model of tire.

Here the general thoughts could be finished. Some practical consideration could be find here: Road bike tires, I want to ride fast but without punctures.

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Vadim Nikitin

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