The answer is yes, it’s necessary. If you are riding on the plain place you may not know why need the speed gears. Once climbing a hill, a cargo bike that won’t change speed may not be able to climb up.
When it comes to speed change, we have a professional term called: rotation ratio. As the name suggests, it is the ratio of the angular velocity of two rotating components in the mechanism, also known as the speed ratio.
As to the chain transmission of cargo bicycle, the ratio of the number of teeth of the driven wheel to the number of driving teeth is the transmission ratio.
People drive the driving wheel (crank tooth disc) by stepping on the pedal to drive the chain, and then drive the driven wheel (flywheel) to rotate the rear wheel to realize the movement of cargo bicycle.
As shown in the Yellow chain in the picture,front is small disc and rear is big dis, this is a large transmission ratio. The larger the driven wheel (flywheel), the larger its power is, and the larger the power is, the more effort is saved, which has been learned in the lever principle. At this time, the driving wheel (crank toothed disc) may have to rotate more than half or one circle, and the driven wheel (flywheel) can only rotate one circle, which shows that it can save labor. Therefore, when climbing the slope, switching to the “small in front and large in rear” mode can climb to the top of the slope easily.
As shown in the red chain in the picture, front is big disc and rear is small dis, the big gear rotates once, and the small gear may rotate several times. It is laborious, but it saves work. That is why we step on it very laboriously but can obtain very high speed. If you use this transmission ratio to climb a slope, the human body may not be able to provide enough strength to drive the transmission system, or the human is strong enough, but the chain cannot bear such a large force and is broken by pedaling, resulting in failure to climb the slope.
The more gears are used, the finer the division between the transmission ratios is, while the maximum and minimum transmission ratios only depend on the number of teeth of the driving wheel (crank tooth disc) and the driven wheel (flywheel). Therefore, you may not feel the change of transmission ratio with too many gears, because there are very slight differences between some gears. It is not worth if too many discs, it will increase the weight of the cargo bike or the risk of gear chain loss.