Understanding Bicycle Spokes: Where Is Your Support Comes From?

Many cyclists and enthusiasts have pondered the mechanics of bicycle wheels, particularly where the support comes from when riding. The common belief is that the rider is either suspended from the rim by the spokes at the tallest point of the wheel or supported by the spokes pushing against the rim and tire at the lowest point. Let's demystify this question by delving into the fundamental principles of bicycle wheel mechanics.

Weight Distribution and Spoke Tension

When you're riding a bicycle, your weight is transmitted through the bicycle frame to the wheels. An upright bicycle transfers the weight of the rider and the bike approximately to the ground through the tires. The critical component that maintains the wheel structure is the spoke. Spokes are essentially tensioned strings that connect the hub (center of the wheel) to the rim (outer edge of the wheel). They work in harmony to maintain the wheel's shape and support the load.

Spoke Tension and Load Distribution

When the bike is stationary, the spoke tension is at its maximum. As soon as the rider starts pedaling, the weight distribution shifts, which in turn affects the tension in the spokes. At the lowest point of the wheel, the tire makes contact with the ground, and this is where the weight is transferred. The spokes at this point help maintain the wheels' integrity by keeping the rim in place and supporting the load.

Here is how it works in more detail:

The weight of the rider and the bike is transferred to the tires, and from there, it is distributed along the ground.

At the lowest point of the wheel, the spokes carry the load. In a bicycle with a 36-spoke wheel, only about 33 spokes are actually supporting the load, with each spoke carrying approximately one-third of the total load.

The rim distorts slightly, with the bottom-most part pushed inward while the rest of the rim is pushed outward. This process increases the tension in the remaining spokes, creating a balanced load distribution.

Sharing the Load Among Spokes

The key concept in understanding the support mechanism of a bicycle wheel is that the load is not just carried by a few spokes at the top or concentrated on just the bottom. In reality, the load is distributed among many spokes. This is why a bicycle wheel can carry a significant load more efficiently than a cart wheel that relies on the compression of a few spokes.

Additional Perspectives

Some experts, such as Jobst Brandt, an eminent mechanical engineer, offer alternative explanations for the spoke support. While these perspectives add depth to the understanding, it's important to note that physical processes can be appreciated from multiple equally valid viewpoints. Sometimes, one explanation may be more comprehensible to non-physicists than the more technical explanations.

For a deeper dive into these topics, consider these resources:

Sheldon Brown website, which provides comprehensive material by John Allen about wheelbuilding. John Allen’s insights from musical instruments offer valuable perspectives on building strong and durable wheels.

Articles by Eric Hjertberg from Wheelsmith Cycles provide excellent information on wheelbuilding techniques. Although the link to the specific article seems to be dead, you can explore other relevant content on his website.

By understanding the mechanics of bicycle spokes, you can appreciate the engineering marvel that keeps you riding smoothly and safely.