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Chains are often narrower than belts, and this can make it easier to shift them to larger or smaller gears in order to vary the gear ratio. Multi-speed bicycles with derailleurs make use of this. Also, the more positive meshing of a chain can make it easier to build gears that can increase or shrink in diameter, again altering the gear ratio.
A gear train or gear set is a machine element of a mechanical system formed by mounting two or more gears on a frame such that the teeth of the gears engage.. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, providing a smooth transmission of rotation from one gear to the next. [2]
Typical gear ratios on bicycles range from very low or light gearing around 20 gear inches (1.6 metres per revolution), via medium gearing around 70 gear inches (5.6 m), to very high or heavy gearing around 125 gear inches (10 m). As in a car, low gearing is for going up hills and high gearing is for going fast.
The speed ratio for a pair of meshing gears can be computed from ratio of the radii of the pitch circles and the ratio of the number of teeth on each gear, its gear ratio. Two meshing gears transmit rotational motion. The velocity v of the point of contact on the pitch circles is the same on both gears, and is given by
One standard option for the Brompton folding bicycle is to use a 3-speed hub gear (roughly a 30% difference between gear ratios) in combination with a 2-speed derailleur gear (roughly a 15% difference) to give 6 distinct gear ratios; this is an example of half-step gearing. Some Brompton suppliers offer a 2-speed chainring 'Mountain Drive' as ...
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Worm-and-gear sets are a simple and compact way to achieve a high torque, low speed gear ratio. For example, helical gears are normally limited to gear ratios of less than 10:1 while worm-and-gear sets vary from 10:1 to 500:1. [45] A disadvantage is the potential for considerable sliding action, leading to low efficiency. [46]
A hub gear, [1] internal-gear hub, [2] internally geared hub [3] or just gear hub [4] is a gear ratio changing system commonly used on bicycles that is implemented with planetary or epicyclic gears. The gears and lubricants are sealed within the shell of the hub gear, in contrast with derailleur gears where the gears and mechanism are exposed ...