The difference between shopping cart caster with bicycle wheel

Supermarket shopping cart, or in the airport luggage cart, below there are 4 casters. Look carefully you can find, castor wheel shaft and car body is not fixed, but can rotate freely around the vertical axis. Because if shaft and car body is fixed, castor will only go straight forward, the car can't making a turn now. In addition can also found that when you push forward, castor always follow behind the axis of rotation. If once into to retreat, castor will suddenly around the vertical axis around 180 °, still follow the location of the axis of rotation. Under normal circumstances, the rolling direction of the caster must be consistent with the direction to make the shopping cart along the local sports. Once the direction of the rolling direction of the caster and inconsistent, the friction of the ground will be to produce in front of the vertical axis of the torque, driving the location of the caster to and walking in the same direction. And shopping cart are of a similar castor bike has a similar phenomenon. If the bicycle front fork of rotation of the extension to the ground, it and the intersection of the ground is always located in the front of the front wheel and the ground contact. When you walking forward cushion carts, the front wheel very obediently follow the direction. If go backwards cart, front wheel and the relative position of the fork on the contrary, the lateral friction driving direction is on the contrary, the front wheel will be swung. Bicycle front fork axis and the relative position between the front wheel and the ground contact, to ensure the driving stability of the bicycle has a very important role. To understand the effect, can produce a special bike, bicycle front fork axis extension cord and the intersection of the ground is located in the back of the front wheel and the ground contact. On this special bike, let your bike how clever technology, bicycles are not stable. Although bicycle since the invention of 200 years of history, but to explain why a stationary bike push fell, but ride up stable mechanics principle and is not easy. Above the position of the front wheel rotation is the important factor affecting the stability of the bicycle, even more important than caster wheel rotates inertia effect.