Tandem bicycle

A tandem bicycle is a vehicle designed for multiple riders traveling in a single line. The term tandem describes the seating arrangement, where riders sit one behind the other rather than side by side.

This distinguishes them from "sociable" bicycles, where riders sit next to one another. Tandems are significant because they allow people with different physical abilities to travel together at the same speed. They are also used in competitive racing and specialized events, such as the Paralympics. In these competitions, sighted captains steer while visually impaired riders act as stokers.

To function correctly, the riders must coordinate their movements through a specialized drivetrain. On most conventional tandems, the two sets of cranks are mechanically linked by a timing chain. This chain ensures that both sets of pedals turn at the exact same rate.

The front rider is often called the captain, pilot, or steersman. This person is responsible for both steering the bicycle and pedaling. The rear rider is known as the stoker, navigator, or rear admiral. The stoker focuses primarily on pedaling to provide power.

There are several ways engineers connect the pedals to the rear wheel. The most common method is called crossover rear drive. In this setup, a timing chain connects the front crankset to the rear crankset. Then, a right-side chain connects the rear cranks to the rear wheel. This requires both rear cranks to have chainrings. Another method is single side rear drive. This uses a right-side timing chain to link the front and rear cranks. A third, less popular method is crossover front drive. This uses a long drive chain from the front to the rear, plus a timing chain.

Because tandems carry more weight, they require specific engineering to handle unique stresses. The extra load affects the forks, brakes, and wheels.

Tandem-specific forks are designed to manage higher weight distribution. Brakes must also be engineered to handle substantial forces. For example, carbon tandem forks must manage increased heat during braking. The wheels often use a higher spoke count or sturdier rims to prevent damage. Because the rear wheel wears out faster, manufacturers may use asymmetric wheels with more spokes on the rear side.

History shows that tandem designs have evolved significantly since the mid-1880s. In 1898, Mikael Pedersen developed a two-rider tandem weighing 24 pounds. He also created a four-rider "quad" that weighed 64 pounds. These bicycles were even used during the Second Anglo-Boer War. While tandem popularity declined after World War II, a revival began in the late 1960s. In 1971, The Tandem Club was founded in the United Kingdom. Later, companies like Santana Cycles were established in the USA in 1976.

Tandems come in many different configurations and sizes. A bicycle for three riders is a triplet, while four riders use a quad. A five-rider bicycle is called a quint.

Some designs allow for independent pedaling. The DaVinci design uses an intermediate shaft and a converter to allow riders to coast independently. There are also recumbent tandems where riders sit in a reclined position. Some models even feature double steering, where both riders can control the direction.

In terms of performance, tandems offer unique advantages on certain terrains. On flat ground or downhill, a tandem can reach higher speeds than single bicycles. This happens because the riders provide double the pedaling power while facing similar wind resistance.

However, climbing hills can be difficult. This is often due to the need for high coordination between riders. If fitness levels differ, riders must compromise on their cadence, or pedaling speed. Despite these challenges, high-performance tandems can achieve incredible speeds. In 2013, a tandem velomobile record of 83 km/h was set.