The first thing we need to know is the relationship between the stress area and the pressure.
The larger the contact area, the smaller the pressure
The smaller the contact area, the greater the pressure
Then the core factors that determine the grip of the tire are the roughness of the contact surface and the size of the contact area, but the contact area mainly refers to the crown width of ordinary tires. Wider tires have greater deformation, which can improve the grip when running at high speed; Generally speaking, it is true that the wider tires have a higher limit of skidding on the snow and ice, and the narrower tires are easier to skid, but the difference is not great for the snow chains.
If the quality of the car remains unchanged, the pressure on the tire remains unchanged. If the pressure remains unchanged, the pressure remains unchanged. There is only one way to change the pressure.
Reduce the contact area
The determinants of pressure are the contact area and positive pressure, which are the same as the determinants of friction (it can be understood in this way); When the positive pressure cannot be changed, the pressure can be increased only by reducing the contact area. Increasing the contact area will weaken the pressure, but for rubber tires, the traction can be improved by deformation; The anti-skid chain or track is made of metal, so this factor is not considered, so the contact surface can be reduced.
Is this explanation still somewhat difficult to understand? In fact, increasing the area can only improve the grip of the rubber tire, but not the friction. A larger contact area is equal to “the roughness of the contact surface is weakened”, and the friction will be reduced if the contact surface becomes smooth.
If the crawler is a bare steel plate, it means that the contact area with the ground is too large. If the pressure is reduced and the friction is low, it will slip. On the contrary, most of the crawler will be concave, leaving only some prominent metal edges in contact with the ground. This is equivalent to reducing the contact area and increasing the roughness of the contact surface (bumps / bumps) to improve the friction. This is the reason why the tracked vehicle basically does not skid. Of course, there are also factors that the tank or excavator itself is very heavy.
The anti-skid chain is imitating the crawler, and the ordinary metal anti-skid chain is almost the crawler, but the car body is too small, and the pressure of matching the metal anti-skid chain is still low, so it is unable to crush the ice on the snow compacted into ice, or the friction at the lifting position is too small, it will continue to slip.
Many anti-skid nails will be installed on the anti-skid chains made of cow tendons. The tips of these nails are only a little, and the tips of some stators are pressed on the ground by the tires; This means that the contact surface is very small. If the pressure remains unchanged and the contact surface is greatly reduced, the pressure will be very high, so that the car body can be pushed forward.
This is the reason why the wheel snow chains will not slip. Only when they can poke into the ice can they prevent slipping, or there is very high friction, which the tire itself cannot do; Therefore, snow and ice driving requires anti-skid chains with anti-skid nails.