# The transmission ratio.

#### The transmission ratio. An average cyclist kicks on a bicycle, the pedals round with about 1 to 2 revolutions per second (60 to 120 revolutions per minute) depending on the effort and condition. The wheels rotate about 1 (at 8 km / h) to 8 revolutions (at 60 km / h) per second. The chain drive with the transmission ensures that the rotation of the crankshaft is converted into a slower or faster rotation of the wheel. This depends on the applied driving system, fixed gear ratio, or derailleur system.

The number of revolutions of the crank per second running is the cadence. In the sport of cycling they are applying in general the number of revolutions per minute. This is called the cadence. When calculating the speed the cadence must be converted to the pedal frequency. The cadence of someone who is untrained or cycle quiet, is around 60 to 90 revolutions per minute. Through good training will get a rider more leg strength and thus can achieve a lower cadence. The cadence of a well-trained cyclist can therefore lie below 60 revolutions per minute. For untrained cyclists it is wise to maintain a high cadence.

The number of teeth of the chain wheel in relation to the number of teeth of the chain determines the difference in rotational speed of the chain wheels. (see Figure 2) . If the chain wheel has 42 teeth and the sprocket teeth 21, then when one revolution of the crankshaft to rotate the rear wheel twice. After all, teeth 42 divided by 21 teeth is 2. The number of teeth of the chain wheel divided by the number of teeth of the sprocket is the transmission ratio. A ratio of 1.5 means that the rear wheel 1.5 times faster or 1.5 times slower turns. This is also dependent on the applied driving system.

The displacement of the bicycle in one revolution of the wheel is dependent on the circumference of the wheel. The degree of displacement in one revolution of the crankshaft is called the resistance of the bike. If the circumference is 2.2 meters and the transmission ratio than the second cycle of revolution of the crankshaft will be 2.2 x 2 m = pass 4.4 meters.

Het verzet van de fiets is dus:

The resistance of the bike is:

(Number of teeth of the chain wheel : number of teeth of the sprocket) x the wheel circumference = distance traveled in meters.

The speed of the bike is the relocation of the cycle per second or per hour. The speed in m / s can be calculated easily:

speed (in m / s) = pedal frequency (revolutions in bottom bracket / s) x resistance (in meters).

To get the speed in km / h, the speed in m / s must be multiplied by 3.6 (times 3600 sec divided by 1,000 meters). The speed of the bicycle is dependent on the pedal frequency, the transmission ratio of the chain and chain wheel and the perimeter of the wheel.

For the selection of the transmission on the bike without gears should be an estimate of the average cadence and average speed at which the customer will cycle. The ratio can be calculated using the following formula: speed in m / s (wheel circumference in meters x cadence) = gear ratio.

At a pedal frequency of 1 rev / sec, a speed of 20 km / h and a circumference of 2.2 meters, the transmission is 2.5. Therefore, the gear ratio in regular bikes is between 2 and 2.5.
Bikes without gears However, the major disadvantage that the speed is directly related to the cadence. With heavy headwinds should be kicked with great force and low cadence. When downwind should be kicked out with little force and high cadence. On bikes with gears can always be cycled with about the same force and cadence if the gears are well chosen.

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