What factors primarily affect the resistance a piece of tubing contributes to a draft system?

The resistance that a piece of tubing contributes to a draft system is primarily affected by the diameter and smoothness of its walls. A larger diameter tubing allows for more beer to flow through it with less friction, thus reducing the overall resistance in the system. Conversely, smaller diameter tubing increases resistance, making it harder for the beer to flow.

The smoothness of the tubing's interior surface also plays a significant role. Smoother walls reduce friction, allowing the beer to flow more freely. Rougher surfaces create more turbulence and resistance, which can hinder the flow rate and lead to issues such as excessive foaming or slow pouring.

Other factors, while they may influence flow rates in some contexts, are not as critical in determining resistance within the tubing itself. For instance, the temperature and pressure of the beer can affect its viscosity and carbonation, but these properties come into play more in the overall system dynamics rather than the resistance of the tubing alone. Similarly, the length of the tubing impacts resistance, but it is the combination of diameter and surface texture that primarily dictates that resistive force. The type of beer being served does not directly affect the tubing's resistance; it may influence flow characteristics at a more systemic level but not the physical properties of the tubing itself