A modern bicycle is a high-tech vehicle on two wheels. Previously, only the "pedal-rear wheel" system was enough for driving, now they have a speed system. It is worth figuring out how many speeds a bicycle can have.
It is in them that the whole point is. The number of bike speeds directly depends on their number. Most bicycles currently produced (road and cross-countrey) have sprockets on both the rear wheel and cassette (where the pedals are). In order to find out how many speeds a particular bike has, you need to multiply the number of chainrings and chainrings. For example, if there are 7 stars in the back and 3 in the front, then the bike is 21-speed.
The number of speeds can vary from 10 (5 stars at the rear and 2 at the front) to 30 (10 stars at the rear and 3 at the front). Bicycle manufacturers usually prefer to produce bicycles with 21 speeds. These are light-alloy bicycles, with a front shock-absorbing fork, designed for riding not only in urban areas, but also off-road. Road bikes with narrow wheels with a diameter of 27 to 31 cm are distinguished by a large number of speeds. Children's bicycles are the smallest.
A little about the correct gear shifting
In order to avoid premature wear of the cassette, chain and gearshift system as a whole, it is necessary to adhere to a number of simple rules. First, you should not change gears while climbing. The tension of the chain is not weak anyway, and even the chain has an instant load while jumping from one star to another. Select the slowest speed for ascent (in other words, select the largest sprocket at the rear and smallest at the front. The speeds are switched for both the rear wheel and cassette. Simply put, the first speed on both derailleurs is selected for ascent).
Secondly, it is worth changing the speed only while riding the bike, when the pedals are spinning. Otherwise, during the start of the bike, a person may hear a not very pleasant sound from the chain. This will affect its wear and tear.
The third rule is that the difference between the speeds (chain stars) should not be more than 4. That is, you should not choose the lowest speed on the front / rear chainring and the highest on the other. This can cause the chain to stretch faster than the chain manufacturer specified. A stretched chain will lead to breakdown of the gearshift system as a whole. This is not a very pleasant and not the cheapest repair. The cost of a good switching system can be more than one thousand rubles.
And the last thing - you need to regularly lubricate the chain. A signal that it is time to do this may be extraneous metallic noise from the chain or a kind of rustle while driving. If the bike is used carefully and not on the road, you will need to wipe the chain with a dry cloth from dirt, and then lubricate with a special bicycle chain lubricant. If the bike is a frequent visitor to country roads or sandy beaches, before lubricating, you will need to rinse the chain with kerosene or a special mixture for cleaning the chain.