Approach Angle
The approach angle, which is primarily relevant to front-wheel-drive, 4WD, 2WD vehicles, becomes crucial when a vehicle navigates level ground towards a towering hill.
If the hill's angle is excessively steep, the front bumper will make contact first, rendering the vehicle unable to ascend. However, if the front tires make initial contact, the vehicle gains the ability to begin its ascent on the hill. This steepest attainable angle for climbing is referred to as the approach angle.
Departure Angle
The departure angle, in contrast to the approach angle, pertains to the rear of the vehicle. Its significance lies in the potential risk of the rear end of the vehicle making contact with the level ground if this angle is less generous than the approach angle. This can occur as the vehicle's incline increases while ascending a hill.
A vehicle's approach and departure angles are primarily influenced by its front and rear overhangs, which represent the extent to which the vehicle's body extends beyond the center of its wheels. Additionally, ground clearance, particularly at the extreme front or rear of the vehicle, plays a pivotal role in determining these angles.
In many instances, there is less overhang in the front compared to the rear. Therefore, when ground clearance is uniform at both ends of the vehicle, the approach angle exceeds the departure angle. Consequently, the front of the vehicle can ascend a steep hill that might cause the rear to scrape the ground during the climb.
However, certain off-road obstacles are not towering hills but rather short mounds, where the front has already surmounted the peak before the rear reaches the bottom. Moreover, in select off-road vehicles, the first contact in the rear may involve tow hooks, which can readily penetrate dirt or sand and navigate over rocks.
Breakover Angle
The breakover angle becomes a critical factor when a vehicle surmounts the hill's pinnacle. The more acute the hill's shape, the greater the breakover angle required to successfully traverse it. This angle is determined by the vehicle's wheelbase and, more specifically, the ground clearance at the center of the vehicle.
Typically, a vehicle's ground clearance is measured from its lowest point, which can either be the front or rear axles (though this is usually not a concern when cresting a hill). This explains why you may observe off-road vehicles elevated significantly above the ground, enhancing the center's ground clearance and enabling them to conquer steeper crests.
In the context of a fixed center ground clearance, the closer the axles are positioned to each other—the distance between the front and rear axles, known as the wheelbase—the more acute an incline's peak angle the vehicle can clear. To achieve an optimal breakover angle, it is advantageous to have a short wheelbase and ample center ground clearance.
If a vehicle's breakover angle falls short of the hill's peak angle, the vehicle's center may scrape against the hill's apex, potentially causing either the front or rear tires to lose contact with the ground. This situation is referred to as being "high-centered."
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