Bicycle Wheel

A bicycle wheel is a specialised wheel designed to support and propel a bicycle. Most modern examples are wire-spoked tension wheels consisting of a hub, a network of tensioned spokes and a rim that carries a pneumatic tyre. A pair of matching wheels is often referred to as a wheelset, particularly when sold as a pre-built unit for performance riding. Bicycle wheels must fit the fork and frame dropouts and accommodate braking, gearing and tyre systems, making wheel design central to bicycle engineering.

Invention and Early Development

The wire-spoked tension wheel now taken for granted originated in aeronautical experiments. The first known proposal for such a wheel appears in a notebook entry by Sir George Cayley dated 19 March 1808, in which he suggested replacing traditional wooden spokes with tight cording to rely on rim tension for strength—a design he later employed in his 1853 glider. Cayley’s idea was the foundation for the tension wheel: a light, strong structure able to support loads while remaining flexible enough to deform under stress without failure.
Early bicycle wheels resembled carriage wheels, using a wooden hub, a fixed steel axle, wooden spokes and an iron tyre. The transition to tension-spoked wheels occurred as bicycles evolved and the need for lower weight and improved durability grew. By the late nineteenth century, wire spokes, metal hubs and pneumatic tyres had become standard.

Construction and Components

Modern bicycle wheels comprise three principal elements: hub, spokes and rim, which together support the tyre and transmit forces between the bicycle and the ground.
HubThe hub sits at the centre of the wheel and contains an axle, bearings and a hub shell. The axle attaches to the fork or frame dropouts. Contemporary hubs may use:

• Quick-release skewers, allowing tool-free wheel removal.
• Threaded axles with nuts, common on track, BMX and lower-cost bicycles.
• Bolt-on axles threaded inside the hub for bolts, sometimes used on single-speed hubs.
• Thru-axles, removable axles inserted through one fork leg, the hub and into the opposite fork leg, providing precise rotor alignment and improved stiffness—now widespread on mountain, cyclocross and increasingly road bicycles.
• Female axles, hollow axles with bolts threaded into each end, especially common in higher-end BMX hubs.

Hub spacing has standardised since the 1980s: front hubs are typically 100 mm wide, while rear hubs for geared road bikes are generally 130 mm, and mountain bikes commonly use 135 mm or wider.
BearingsBearings allow the hub shell to rotate freely around the stationary axle. Two main systems exist:

• Cup-and-cone bearings, using loose balls running between a fixed cup in the hub shell and an adjustable cone on the axle. These are durable and serviceable but require precise adjustment.
• Cartridge bearings, sealed units pressed into the hub shell, replaceable as a whole but not normally serviceable. They often offer superior sealing and consistent manufacturing tolerances.

Hub shell and flangesHub shells typically have two outward flanges with holes to accept spokes. Flange diameter and spacing affect wheel stiffness: larger diameters improve torsional stiffness and allow more spoke holes, while wider spacing yields better lateral stiffness. Variations include hidden spoke attachments or threaded hub shells.
Hub brakesSome hubs integrate or support braking systems:

• Disc brake mounts allow rotors to be bolted or locked onto the hub.
• Drum brakes house brake shoes that expand against the inside of the hub shell; often used on tandems for sustained braking.
• Coaster brakes provide back-pedal braking built into the rear hub.

Gearing mechanismsRear hubs may include or support several gearing systems:

• Freehub bodies accept cassettes and incorporate a mechanism enabling coasting.
• Threaded hubs allow attachment of separate freewheels.
• Track hubs have opposing threads for a fixed sprocket and lock-ring, with no coasting mechanism.
• Flip-flop hubs have threads on both sides, allowing a rider to reverse the wheel to change gear.
• Internally geared hubs enclose multi-ratio gearing within the hub shell.

Rims and Tyre Support

The rim provides the outer structural component of the wheel and supports the tyre. Modern rims are usually aluminium extrusions formed into hoops, though carbon fibre rims are common in performance cycling and wooden rims historically preceded metal designs. Some wheels combine aluminium braking tracks with carbon fibre aerodynamic shells.
Rim design reflects the intended braking system:

• Rim-brake rims include flat, parallel braking surfaces.
• Disc-brake rims may omit braking surfaces entirely.
• Westwood rims, among the earliest designs, are shaped for rod-operated brakes acting on the inside of the rim and cannot be used with standard caliper brakes.

Rim cross-sections vary widely to optimise aerodynamics, mass, stiffness, durability or compatibility with tubeless tyres. Double-wall and reinforced profiles are common in modern designs.

The Role of Spokes

Spokes in a wire wheel work almost entirely in tension. They connect the rim to the hub and create a pre-stressed structure that supports loads by redistributing forces across multiple spokes. Patterns such as radial, two-cross, three-cross or four-cross lacing influence strength, stiffness and the wheel’s ability to transmit braking and pedalling torque.

Wheel Performance and Specialisation

Wheel design must account for factors such as weight, stiffness, aerodynamic drag, impact resistance and intended use. Road racing wheels prioritise lightness and aerodynamics; mountain bike wheels often emphasise strength and impact resistance; touring wheels focus on durability and serviceability. The concept of the wheelset has facilitated the production of optimised matched pairs, allowing cyclists to tailor performance characteristics.

Evolution and Continuing Innovation

From Cayley’s early tension wheel to modern carbon-composite aerodynamic rims and sophisticated hub mechanisms, the bicycle wheel has undergone continuous refinement. Despite changes in materials and technologies, the wire-spoked tension wheel remains fundamental due to its remarkable combination of strength, lightness and efficient load distribution. Modern innovations continue to build upon this proven principle, adapting wheel design to new cycling disciplines, braking technologies and performance demands.