Bicycle wheel some other fixed point may be used as a reference mark, however this is less accurate. At one end of each spoke is a specialized nut, called a nipple, which is used to connect the spoke to the rim and adjust the tension in the spoke. The nipple is usually located at the rim end of the spoke but on some wheels is at the hub end to move its weight closer to the axis of the wheel, reducing the moment of inertia. Until recently there were only two types of nipples: brass and aluminum (often referred to as "alloy").
Wheel hub motor occurs as the rotor first begins to turn, which is why electric motors do not require a transmission. A gear-down arrangement may be needed, but unlike in a transmission normally paired with a combustion engine, no shifting is needed for electric motors. Wheel hub motors are increasingly common on electric bikes and electric scooters in some parts of the world, especially Asia. Compared with the conventional electric vehicle design with one motor situated centrally driving two (sometimes four) wheels by axles, the wheel motor arrangement has certain advantages and disadvantages: Cars with electronic control of brakes and acceleration provide more