This is an interesting question! What tires should the strongest off-road vehicle use? It seems even MT (Mud Terrain) tires can slip. So, what can truly handle muddy roads like they're flat ground? The answer is "tracks." Bulldozers, excavators, or tanks-vehicles with tracks don't seem to slip.
Let's set aside the differences between tracks and wheels for now and first understand the relationship between force area and pressure.
Larger force area = Smaller pressure
Smaller force area = Greater pressure
The ratio of the pressure applied to an object to the force area is called pressure. Simply put, the greater the pressure, the greater the force exerted.
Tire friction is determined by three main factors, and the tire's grip requires an additional factor:
Surface roughness of the contact area
Positive pressure
Contact area
Friction depends on the first two factors. Only when friction is strong enough can the tire avoid slipping. However, positive pressure is constant-the vehicle's curb weight remains largely unchanged, and only the combined weight of the driver and passengers will have a small impact.
So, the core factors determining tire grip are surface roughness and contact area. The contact area mainly refers to the tire's width. Wider tires can deform more, improving grip at high speeds. Generally, wider tires are more prone to slipping on snow and ice, while narrower tires are less likely to slip. But the difference is minimal when using anti-skid chains.
If the vehicle's mass stays the same, the pressure on the tire remains unchanged. If pressure remains constant, the only way to increase it is by reducing the force area.
Pressure depends on both the force area and the positive pressure-just like friction depends on surface roughness and contact area. If positive pressure cannot be changed, the only way to increase pressure is to reduce the contact area. However, a larger contact area would reduce the pressure, and for rubber tires, this can improve grip by allowing the tire to deform. But for anti-skid chains or tracks, which are made of metal, deformation is not a factor, so the contact surface can be reduced.
This explanation might be a bit tricky to follow, so let's simplify it. Increasing the contact area only improves the grip of rubber tires, but not the friction. A larger contact area actually reduces friction because it leads to a smoother contact surface.
If a track was made from a smooth steel plate, its contact area with the ground would be too large, resulting in reduced pressure and low friction, causing it to slip. However, most tracks are designed with recessed sections, leaving only the protruding metal edges in contact with the ground. This reduces the contact area and increases the roughness of the contact surface (bumpy/uneven), which in turn increases friction. This is why tracked vehicles generally don't slip, although the weight of tanks or excavators also helps.
(Though the wheels of the track are smooth, they are only load-bearing wheels. The drive wheels are specially designed to connect with the track.)
Anti-skid chains mimic tracks. Metal anti-skid chains are similar to tracks, but since the car's mass is much smaller, the pressure exerted with metal chains is still low. It's not enough to crush the ice or snow layer compacted into ice. The friction at the release position is too low, which leads to continued slipping.
Many anti-skid chains are equipped with spikes made of cow tendon. The tips of these spikes are small, and the tires press on the ground with just the tips making contact. This means the contact surface is extremely small, keeping pressure unchanged but greatly increasing it. The high pressure allows the spikes to penetrate the ice, which helps push the car forward.
This is why tires equipped with anti-skid chains don't slip. Only chains that can penetrate the ice or those with extremely high friction can prevent slipping-something the tires themselves can't achieve. Therefore, driving on snow or ice requires anti-skid chains with spikes or modified track wheels (though the latter is costly and impractical).
In summary: Anti-skid chains with spikes increase pressure and friction on slippery surfaces, helping the tires grip the ground and preventing skidding.