Why do bicycles have gears?

Answer 1

Because when you switch between them you can leave the rider to push the pedals in a comfortable pace regardless if the road is ascending or descending. Prettty much the same thing as changing gears in a car to leave the engine in a rpm range where it'll work efficiently.

Answer 2

Humans, and engines, works best at a certain rate of turns. With gears the rider can stay at that rate regardless of going fast or slow.

First rule is to maintain a steady cadence(i.e.revs-per-minute on the pedals). General recommendations is that one of your feet should pass through the bottom of the pedal stroke 70-100 times each minute. Pedalling faster isn't particularly dangerous, but difficult and not very effective. Pedalling slower will increase the load on your knees, which in turn increases the risk of injury.

Second rule is to keep the chain straight(avoid cross chaining). More important if you hav 3 sprockets to choose from at the front than if you've only got two, but always worth considering. Running the chain at opposite ends of the sprockets (big-big, or small-small) will put a significant bend on the chain which apart from wearing the chain out faster also will add a few percent of extra friction.

3rd rule would be that bigger sprockets are better. The smaller the sprocket the bigger the losses, so switching to a bigger front sprocket rather than dropping to a smaller rear sprocket will be better in terms of efficiency by a few percent.

Answer 3

The reason for different gears on anything is to enable the "motor" to run the machine at its peak efficiency. Powerful motors in automobiles, operate between about 800 and 7000 RPM--depending on model. Humans as motors are limited to about 60 to 120 RPM and only about 1/4 horsepower. To keep the pedaling RPM in that narrow band, gears are used to turn the wheel faster or to handle a load--like climbing a hill.

Answer 4

Bicycle gears, as almost all gearing systems, is a way of trading strength for speed, or speed for strength.

It allows the rider - the motor - to keep turning the pedals at a comfortable pace and resistance regardless if the ride is flat, uphill or downhill.
Because your body, just like an engine, works best at a certain rate of turn. Gears allow you to keep turning the pedals at somewhere between 80-100 turns/minute (where your body is happiest) and at the same amount of resistance regardless if you're going uphill slowly or flying along on the flat with a nice tailwind helping you along.

Gears allows you to trade power for speed and the other way around when the riding conditions calls for it. Heading up you trade speed for power by shifting down, heading down you trade power for speed by shifting up.
The same as gearing on any mechanical device. They enable the power source (in this case, you or me) to operate at a reasonably efficient pace, while translating that power into slower or greater speed depending on the amount of resistance that the vehicle is facing.

The power source can only produce a certain amount of energy in a given time frame, so you have to modify the amount of work done to compensate. That's why mountain bikes (like mine) have so-called "granny gears" with a very low ratio. When you're geared way down, you pedal a lot but your bike doesn't move very fast, letting you climb a steep hill more easily. If you tried to move more quickly your body couldn't produce enough power to act against the effect of gravity trying to pull you back down the hill.

On the other hand, when you're on a flat surface and already moving quickly you've overcome any starting resistance and only have to worry about rolling friction in the gearworks and between the tyres and the road. You can shift to a higher gear where you continue to pedal at the same pace but each stroke is translated into a longer distance because you're not fighting gravity.

Because your legs, just like the engine of a car, works best at a certain rate of turn. If the slope is too steep for the rider to keep cranking at the appropriate rate it's more efficient to drop a gear and keep the rate rather than getting off and walk or straining at the pedals. Likewise on a downhill it's better to go to a higher gear than to try spinning your legs off.
Gears are used to multiply the power gained from pedalling, to increase or decrease the force either up or down depending on which gear is used.

Answer 5

The purpose of the front gears is the same as the purpose of the rear gears, they allow you to change the gear ratio. The ability to change gears allows you to keep pushing with a force and a rythm that suits you, regardless if you're riding on the flat, uphill, or downhill.

The step between one gear and another is bigger at the front than the steps between gears at the rear, so basically you do the rough adjustment with the front and then fine tune with the rear.

Answer 6

Because your legs, just like the engine of a car, works best a certain rate of movement and a certain load.

A gear that gets you moving easily will have you cranking your legs like crazy w/o getting up to speed while a gear that keeps your legs spinning at a reasonable rate when going fast will be very heavy to turn from a standstill. The ability to change gears allows you to keep pushing with a force and a rythm that suits you, regardless if you're riding on the flat, uphill, or downhill.

Answer 7

In simple terms, big gears turn smaller gears faster and small gears turn bigger gears slower. If the larger gears were in back peddling would take less force but you would have to pedal much faster to move at the same speed you do with the gears the way they are.

Answer 8

There are seldom only 2 gears on a bike. Many have 12, 18 or 21 .