8. Rolling Resistance

Rolling resistance is nothing but what is the resistance offered by the hauled route to the wheel which is rolling over the particular surface. So, what is the resistance offered by the hauled route to the wheel which is rolling over the particular surface, so that is what is your rolling resistance. So, resistance to the motion of equipment on a level surface is called as rolling resistance.

Rolling resistance refers to the force resisting the motion of a wheel rolling on a surface. It is essentially the friction between the wheel and the surface it rolls over. Unlike sliding friction, which occurs when an object slides across a surface, rolling resistance is generally lower. It can vary based on the characteristics of the surface and the type of tires used on the equipment.

Imagine riding a bicycle on two different surfaces: a smooth asphalt road and a gravel path. On the asphalt, you find it easy to pedal and maintain speed since the road is smooth, leading to less resistance. On the gravel path, pedaling becomes harder and more tiring due to the increased rolling resistance from the uneven surface. This analogy illustrates how different surfaces can affect performance.

Basically, we can compare the rolling resistance between hard road and a soft road. So, hard road, you can say a concrete road, your asphalt all these are examples of hard road, your earthen roads are soft road. So, earthen roads, it varies a lot, it depends upon how you maintain it and prepare the earthen roads.

Rolling resistance is significantly influenced by the type of surface the wheels are rolling on. Hard roads like concrete or asphalt generally provide lower rolling resistance compared to soft roads like earthen or unpaved paths. If earthen roads are well-maintained with proper drainage and compaction, they can perform comparably to hard surfaces. However, if they are poorly maintained, for instance, during rainy weather, their resistance could increase, making movement more difficult.

Think of a well-maintained garden pathway made of compacted soil compared to a muddy, uneven field. If you walk on the pathway, it's much easier and requires less effort, while on the muddy field, you're likely to sink in and struggle with each step due to the higher rolling resistance. This shows the importance of maintaining road surfaces.

If it is wheel mounted, even your dimension of your tyre, the tread dimension of your tyre and the inflation pressure of your tyre, all these things are going to affect your rolling resistance.

The design and condition of tires have a direct impact on rolling resistance. Factors such as the width of the tire tread and its inflation pressure play crucial roles. A narrow, fully inflated tire on a hard surface will have a reduced contact area, resulting in lower resistance. Conversely, on a soft surface, a wider tire with lower inflation pressure can distribute weight more effectively and reduce sinking, thus lowering rolling resistance.

Consider a car tire versus a truck tire. Truck tires are wider and designed to take on heavier loads without sinking into soft ground. If you try driving a car with narrow tires on soft sand, those tires would sink, causing the car to get stuck. This illustrates how different tire designs are suited for different surfaces and conditions.

So, this rolling resistance you can even call it as wheel resistance or track resistance depending upon what type of mounting your machine is going to have.

Rolling resistance can also be referred to as wheel resistance or track resistance, depending on whether the equipment is mounted on wheels or tracks. It's important to quantify this resistance to ensure the machinery is appropriately powered for the conditions. Rolling resistance is usually expressed in terms of tractive effort, often measured in kilograms or pounds per ton of equipment weight over a level surface.

Imagine you have two options for moving a heavy load: a wheeled cart and a tracked vehicle. The wheeled cart might operate on a smooth surface needing less force to move, while the tracked vehicle, designed for rough terrain, may have higher rolling resistance on hard ground but could be more efficient on softer paths. This duality reflects how equipment selection hinges on understanding rolling resistance.

Let us see how to estimate the penetration resistance. Say when a tire penetrates into a surface, so the resistance, the rolling resistance increases.

Rolling resistance can be divided into surface resistance, which is the resistance encountered when a tire rolls over the surface, and penetration resistance, which arises when a tire sinks into that surface. For soft surfaces, as the tire penetrates, it requires additional effort to keep moving, leading to increased resistance. Understanding both components is essential for accurate calculations regarding required power.

Think of trying to walk on soft sand. As your foot sinks into the sand, it requires more effort to lift your foot and move forward, which is akin to how a vehicle's tires generate increased resistance the more they sink into soft ground. This is why equipment designed for soft surfaces has larger, wider tires.

Now, for better understanding, let us work out a problem on calculation of the tractive effort. So, calculate the tractive effort generated by a hauling equipment, it is gross weight is given as 50,000 kg, it is traveling on a haul route.

In this section, we are applying the theoretical concepts of rolling resistance to a practical calculation. Given the vehicle's weight and the rolling resistance value from literature, along with the penetration depth, we can compute the total tractive effort required to overcome resistance on the specific surface. This is crucial for selecting the right equipment that can provide sufficient power for moving loads efficiently.

Imagine trying to figure out how much force is needed to push a heavy box across a carpet versus a smooth floor. Knowing both the weight of the box and the friction from each surface allows you to assess how much help you'll need. Similarly, in engineering, measuring resistance lets us choose the right machinery for the job.

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