Bicycle wheel
The first wheel to use the tension in metal spokes was invented by Sir George Cayley to achieve lightness in his 1853 glider.
The rim is commonly a metal extrusion that is butted into itself to form a hoop, though may also be a structure of carbon fiber composite, and was historically made of wood.
Some wheels use both an aerodynamic carbon hoop bonded to an aluminum rim on which to mount conventional bicycle tires.
A separate airtight inner tube enclosed by the rim supports the tire carcass and maintains the bead lock.
Various "hook" (also called "crochet") designs emerged in the 1970s to hold the bead of the tire in place,[9][10] allowing high (6–10 bar, 80–150 psi) air pressure.
Stainless steel spokes are favored by most manufacturers and riders for their durability, stiffness, damage tolerance, and ease of maintenance.
Non-stainless steel spokes on older or cheaper bikes are sometimes surface-treated by galvanization, paint, or, more rarely, chrome plating, and can rust eventually.
Conventional wheels with spokes distributed evenly across the circumference of the rim are considered more durable and forgiving to poor maintenance.
Thus it is generally preferred to build a crossed-spoke wheel where torque forces, whether driving or braking, issue from the hub.
As with any structure, however, practical usefulness is not always agreed, and often nonstandard wheel designs may be opted for solely aesthetic reasons.
"Vertical truing" refers to adjustments of local deviations (known as hop) of the radius, the distance from the rim to the center of the hub.
In addition to the three geometrical aspects of truing, the overall tension of the spokes is significant to the wheel's fatigue durability, stiffness, and ability to absorb shock.
It is also possible to true a wheel while it is mounted on the bike: brake pads or some other fixed point may be used as a reference mark, however this is less accurate.
[28][citation needed] A wheel can be formed in one piece from a material such as thermoplastic (glass-filled nylon in this case), carbon fiber or aluminium alloy.
[29][failed verification] Carbon fiber is typically[weasel words] used for high-end aerodynamic racing wheels.
A full disc is usually heavier than traditional spoke wheels, and can be difficult to handle when ridden with a cross wind.
A compromise that reduces weight and improves cross wind performance has a small number (three or four) tension-compression spokes molded integral to the rim – also typically carbon fiber.
[30] Mountain bike wheels are described by the approximate outer diameter of the rim plus a wide, ~2+ inch tire.
27.5-inch mountain bike wheels[32][33][34][35][36] (which some also refer to as 650B[37][38] use a rim that has a diameter of 584 mm (23.0″) with wide, knobby tires (≈27.5 ⋅ 2.3 / ISO 58-584) are approximately the midway point between the 26-inch (ISO-559mm) and the 29-inch (ISO-622mm) standards.
Their rim diameter of 622 millimetres (24+1⁄2 in) is identical to most road, hybrid, and touring bicycle wheels, but they are typically reinforced for greater durability in off-road riding.
32 inch / ISO 686 32-inch wheels have been in use on unicycles and have been appropriated for bicycles to create bikes more proportional for taller riders.
Usually 20 inches in diameter (rim diameter of 406 mm), BMX wheels are small for several reasons: they are suitable for young and small riders; their lower cost is compatible with inexpensive bicycles; the size makes them stronger to withstand the additional loads generated by BMX jumps and stunts; and to reduce rotational inertia for easier wheel acceleration.
Bicycle rims and tires came in many different types and sizes before efforts were made to standardize and improve wheel/tire compatibility.
The International Organization for Standardization (ISO) and the European Tyre and Rim Technical Organisation (ETRTO) define a modern, unambiguous system of sizing designations and measurement procedures for different types of tires and rims in international standard ISO 5775.
Children's bicycles are commonly sized primarily based on wheel diameter rather than seat tube length (along the rider's inseam) dimension.
The 28 × 2.00, ISO 50-622 onwards, as a marketing term for wide tires for mountain bikes, are known as 29 inch for their larger wheel diameter and measured in decimal sizes.
[49] "Rolling resistance increases in near proportion as wheel diameter is decreased for a given constant inflation pressure.
The hub flanges of modern tension-spoked bicycle wheels are always spaced wider than where the spokes attach to the rim.
When viewed in cross section, the spokes and hub form a triangle, a structure that is stiff both vertically and laterally.
Thus "dishing" is also used to describe the process of centering the rim on the hub, even in the case of symmetrical wheels.
