A bicycle inner tube is an inflatable, elastic container, primarily installed between the outer tire and the rim. Its core functions are to provide airtightness, support, and shock absorption. It is typically made of rubber or other elastic materials (such as butyl rubber, natural rubber, or TPU), and has a tubular structure sealed at both ends to maintain gas pressure.
The main structural characteristics of inner tubes include:
Material Composition: Most use a composite formula of butyl rubber or natural rubber. Butyl rubber has excellent airtightness, with an air permeability eight times lower than natural rubber, allowing it to maintain tire pressure for extended periods. Modern high-end inner tubes may also use TPU (thermoplastic polyurethane), offering advantages such as extreme lightweight and low rolling resistance.
Airtightness Design: The inner tube itself needs to have high airtightness to prevent slow gas leakage. Butyl rubber inner tubes, due to their dense molecular structure and good self-sealing properties, are currently the mainstream choice.
Valve Structure: The valve is a key component of the inner tube, and there are three common types: Schrader, Presta, and Dunlop.
Presta valves are thinner and longer, commonly found on road bikes, and suitable for high-pressure environments. Schrader valves are thicker and mostly used on mountain bikes and city bikes. Dunlop valves use a double-layer rubber sleeve seal, making maintenance convenient but with poorer air tightness.
Valvets have a one-way valve structure, allowing air to enter but preventing leakage.
Matching Requirements: The inner tube size must match the outer tire and rim. Common specifications include 700c and 26 inches, and the width must also correspond (e.g., 19-23C) to ensure a tight fit and prevent twisting or leakage during installation.
Seamless Design: Modern inner tubes mostly use a circular, seamless design, solving the problem of leakage in traditional seamed inner tubes, while also improving overall strength and uniformity.
