Design
The gears on a bicycle are designed to work specifically with a bicycle drive chain. The teeth in the gears are machined so that each tooth fits into the spaces in the chain. As the rider pedals the bicycle, the chain wraps around the front gear, moving onto the gear at the top and off at the bottom. As the gear is pedaled, the teeth grab the chain, turning it as well. This force is then transmitted by the chain to the rear gears that drive the rear wheel and make the bicycle move forward.
Gear Ratios
Multiple gears on a bicycle allow for better pedaling strength in different cycling situations. For instance, set the front bicycle gear to the larger sprocket and the rear gear to a smaller sprocket to provide the highest gear ratio and the most power. This setting is good for cycling fast in relatively flat terrain. Hill climbing, on the other hand, is easier if a lower gear ratio is used. In this case, set the smaller sprocket on the front with one of the larger sprockets of the rear gears. Remember, shift up for uphill riding and shift down for downhill.
Front Gears
The front gear set attaches to the crank assembly, where the pedals are on a bicycle. This gear set usually has three fixed sprockets ranging from small to large, which turn only when a bicycle is pedaled. When riding, set the front gear to the middle sprocket. This provides an adequate range of gear ratios, except in extreme situations, when the larger or smaller gear may be used.
Rear Gears
The rear gear set is on the right side of the rear wheel and consists of a cluster of several sprockets, from small to large, mounted on the axle. Gear sets contain a ratchet assembly that allows the wheel to spin but the gears to remain still. When pedaling, the ratchet engages and the gears lock in place to allow the chain to drive the rear wheel. There are two types of rear gear sets available. The freewheel type threads directly onto the hub of the wheel. The cassette type locks in place onto a hub body, which is threaded to the hub. This makes the cassette type easy to remove and change.
Derailleurs
A derailleur is the device that moves the chain from sprocket to sprocket on a gear set and is used to change the gear ratios to best suit cycling conditions. There are usually two derailleurs on a multi-speed bike. The front derailleur is attached to the frame and fits around the chain near the front gear set. As the chain moves along one of the sprockets in the gear set, the shift lever actuates the front derailleur to move left or right against the chain. This pushes the chain up or down to the desired sprocket. The rear derailleur is a mechanical armature mounted on the frame near the rear axle. This derailleur is spring loaded to keep constant tension on the chain. The rear derailleur is also actuated by a shift lever and moves the chain up or down the rear gear set.
Shifters
A set of gear shifters, which can be a pair of levers or twist grips mounted on the handlebars, will actuate the derailleurs to shift gears by means of wire cables that run from the shifters to the derailleurs. The shifters allow the rider to move from gear to gear smoothly while riding. It is important not to shift when the chain is under direct pressure, as this can damage the sprockets or derailleurs.
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