Vehicle patency is the ability to overcome various obstacles. We are going to consider what vehicle patency depends on, what parameters and indicators affect it.

  • Clearance
  • Suspension
  • Mover pressure on the ground
  • Overhang angles
  • Drive unit
  • Power and torque
  • Geometric patency
  • Tire type
  • Weight distribution of equipment
  • Optional equipment

   Clearance is the same as ground clearance, that is the distance from the ground to the bottom of the car. The higher the clearance, the better the cross-country ability or patency. The clearance depends on the diameter of the wheel. In a good wheeled all-terrain vehicle, the clearance is slightly less than its diameter. In standard cars, the clearance is around 200 mm; this ground clearance does not allow ordinary cars to drive on dirt roads with a developed track. Conventional wheeled all-terrain vehicles and ATVs have a clearance in the range of 240-290 mm, which allows them to move on impassable roads, including dirt roads with a developed track. Off-road trucks have a clearance of 300 mm to 400 mm. Thus, on a dirt road grounded by trucks, it is possible to talk about predicted continuous movement only for all-terrain vehicles with a clearance of 350 mm or more.

   Suspension is responsible for smooth ride and grip. In the absence of suspension there is no smoothness. All shock load falls on the axles of the all-terrain vehicle and its transmission, which leads to its rapid failure. The axles and half shafts of the wheels break while the oil seals go out of order. Moving on such an all-terrain vehicle off-road at normal speed is impossible due to strong shaking. The spine of all-terrain vehicle passengers is under severe stress. In the absence of suspension or when the suspension travel is very small, if you move in off-road conditions, periodic hanging of wheels, that is separation of wheels from contact with the surface, occurs. Naturally, this negatively affects the patency.

  Mover pressure on the ground. In general, reduced ground pressure contributes to increased cross-country ability. Of course, there are exceptions - this is when weak soils have a thickness of about 20 cm, in this case the patency is higher for heavy equipment, which can cut through weak soils with its own wheels, reach solid ones and move on them. Reducing ground pressure is achieved by the following measures:

1. increase in tire width;

2. decrease in tire pressure, which leads to an increase in the contact patch of the tire and the ground;

3. installing oversized wheels (However, this decision leads to an increase in the mass of the wheels, a greater weight of equipment and a greater load on the transmission and engine);

4. increase in the number of wheels;

5. installing low pressure tires on the vehicle. The pressure of such tires on the ground is very low, almost like a tracked vehicle. They almost do not damage the vegetation during their movement. Besides, they have high patency. However, these wheels also have their disadvantages. The installation of low pressure tires on the equipment that was not originally intended for them leads to unnecessary loads on the transmission and engine. The half shafts of this equipment break down almost every trip. Due to the fact that the pressure on the ground of such wheels is low, their adhesion to the surface is also low, so it is often impossible to move uphill on slippery soils using such vehicle. An icy slope, a slope on which snow melts, wet grass on a slope, a smooth, moist clay slope are serious, often insurmountable obstacles for such a technique. Also, transport on low-pressure tires feels very bad on rivers where there is at least a small current. Although the installation of low-pressure tires leads to the transformation of vehicles into amphibious all-terrain vehicles, they are practically uncontrollable on water, their speed is minimal, and if there is a current, it is impossible to predict their movement on water. Also, low pressure tires have much lower strength than conventional tires. It is not difficult to puncture them. The installation of low pressure tires leads to a significant increase in the size of the all-terrain vehicle up to the impossibility of their use on public roads.

   Overhang angles. These are angles formed by the surface of the earth, the wheel and the body of a vehicle. The higher the angle of the overhang, the higher the geometric cross-country ability. Ideally, the all-terrain vehicle wheel extends beyond the body.

   Drive unit. For off-road vehicles they try to use four-wheel drive, i.e. when all axles of the vehicle can spin at the same time. The ideal variant is when all wheels can spin at the same time.

   Power and torque. In fact, the engine power in horsepower is not some serious indicator for cross-country ability. Heavy off-road trucks and even tanks (from the Second World War) have less power than many modern SUVs and much less than sports cars. The lower limit for all-terrain vehicles goes around 10 hp. And the engine power in the range of 20-40 hp is quite sufficient for an all-terrain vehicle. Another thing is the torque, which is very important for an all-terrain vehicle. The torque provides starting and the all-terrain vehicle ability to move through deep mud. Considering a conventional all-terrain vehicle, it is necessary to note the importance of the structural strength of the motor-transmission-chassis. In off-road conditions, all these elements are mechanically connected to each other and are dependent on loads. If you get stuck in the mud, when the wheels do not spin, the drivers try to leave, pressing the gas with all their might. At the same time, the torque, that is transmitted from the motor to the transfer case and gearbox, is able to break these components of the machine. If the strength of the engine and gearbox is high, then stuck, with the wheels locked, you can break the cardan shafts or axles of the wheels, trying to scroll them. At the same time, with a high load on the torsion of the wheels when driving on the road, the motor experiences an increased load and is able to fail at any time. But, for example, an electric or hydraulic drive does not have such problems on the road.

   Geometric patency. This is the ability of an all-terrain vehicle to overcome various obstacles such as slopes, ditches, pits, etc. As for ground clearance and overhang angles, we have already considered them. We should also note the ramp angle. This is the maximum angle that the technique can overcome without touching the bottom of the surface. This angle depends on the wheelbase of the vehicle. For small all-terrain vehicles with more than 4 wheels, this angle does not exist.

  Tire type. When switching from highway to marsh tires, the cross-country ability of an all-terrain vehicle increases significantly.

   Weight distribution of equipment. To improve cross-country ability, it is beneficial that the center of gravity of the all-terrain vehicle is as low as possible and distributed evenly along all axles. For example, the Green Scout all-terrain vehicle is designed with the perfect weight distribution. One-third of the mass of the all-terrain vehicle falls on the wheels, which are located evenly on the sides of the vehicle and are naturally below the hull, which increases its stability when driving on slopes. A third of the mass falls on the batteries, which are located in the center of the all-terrain vehicle and are mounted in its bottom. The remaining third of the mass is distributed evenly throughout the body of the vehicle.

   Optional equipment. An all-terrain vehicle needs a winch. And it is not because a winch is used to pull it out of the mud. When crossing rivers or climbing slopes, it often turns out that the steepness of the slope exceeds the capabilities of any all-terrain vehicle. Whereas using a winch allows you to raise the all-terrain vehicle up a steep wall. For an amphibious all-terrain vehicle, the presence of a boat motor is also desirable - this will increase the speed of movement along the water surface, and in the case of crossing rivers with a fast current, it ensures the possibility of forcing such rivers. The presence of an awning and a stove is really essential, too – although this does not directly reflect on the off-road qualities of the all-terrain vehicle, but creates comfort for the driver and passengers, which will allow them to solve off-road driving tasks more successfully. As for availability of free space on the all-terrain vehicle, it will allow you to take with you various tools and devices, such as additional ropes, a chainsaw, an ax, a shovel, an earth anchor or a generator, that will help you move on the road more safely.