The rear chainring block is designed to extend the gear range so you can choose the most suitable gear. The smallest chain ring makes it difficult to pedal, and the largest one makes it easier. When choosing a block, it is very important to pay attention to how many gears the bicycle has, how the block is fixed on the bushing drum - it can be either a cassette-mounted one or a screw-on one, which is usually installed in cheaper bicycles. There are blocks for road or mountain bicycles. Road bicycle blocks are smaller and more compact, therefore they are intended for fast riding. Mountain bicycles need a very wide range of gears to be able to do both ascend steep hills and ride fast enough on the road. As technology advances, rear chainrings become stronger, lighter, and provide smoother shifting.