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Rolling resistance is a parameter that counteracts the rotational movement of the wheels on lift trucks or stacker trucks. A high rolling resistance leads to higher energy consumption as well as a higher degree of effort when moving manual transport equipment.
Resistance, also known as rolling friction, is not a constant. It is highly dependent on the type of tyre and its rubber compound, the tyre dimensions, as well as variable factors such as tyre pressure or the floor surface. Unlike starting resistance, which refers exclusively to the amount of force required to start a vehicle, rolling resistance is the permanent force generated when a wheel rolls and is directed in the opposite direction to the movement. This guide aims to show you how to calculate and optimise these resistance forces.
Factors that influence rolling resistance for tyres
The following factors must be considered when determining rolling resistance. Some are directly dependent on the tyre, others can be changed independently of the tyre.
The lower the tyre pressure, the higher the resistance that must be overcome when starting. Therefore, all means of transport – from forklift trucks to sack trucks – should always have optimal tyre pressure. Under no circumstances, however, should the tyres be overinflated to the point of posing a safety hazard. Before replacing tyres, first check whether incorrect tyre pressure is responsible for high rolling resistance.
Quality of the tyre
A harder surface material generally allows the tyre to roll more easily and provides less resistance. However, if you opt for tyres made of a hard rubber compound, you should also ensure that the driving and braking characteristics are not negatively affected. The ideal choice of tyre rubber is therefore essentially dependent on the surface.
For example, slippery surfaces, such as tiles or linoleum, require a softer air-filled rubber, which offers better grip properties with good rolling resistance at the same time. Hard surfaces, such as asphalt or rubber flooring, are suitable for tyres made of nylon or polyurethane. Tyres made of foamed polyurethane have several advantages. The almost maintenance-free PU tyres have a comparatively low rolling resistance, even on demanding surfaces, while at the same time providing good shock absorption.
Tyres made of polyamide (nylon) provide the lowest rolling resistance on hard surfaces. Thanks to their resistance to grease, alkali and acid, these tear-resistant tyres are used on surfaces in hygienically sensitive or other demanding areas.
Modern fuel-saving tyres are characterised by a resistance-optimised construction that reduces the deformation of the tyre while driving. This deformation, along with the choice of material, is largely responsible for the rolling resistance.
Wide and flat wheels have a higher rolling resistance than narrow and high ones. However, choose the tyre dimension that matches the means oftransport to achieve optimum results.
Older, rolled-out tyres and worn-out bearings make it harder to move trucks or forklifts than new ones. However, even new tyres may temporarily have more resistance until they are broken in. In this case, continuously monitor the rolling resistance and replace the tyres if necessary.
Road or floor surface
Finally, the ground or road surface also affects rolling resistance. It makes a noticeable difference whether a trolley runs over linoleum, concrete, asphalt or sand. If yourwarehouse has a high throughput, you should choose a floor covering that reduces rolling resistance in the long term.
How to: instructions for how to calculate rolling resistance
- Calculating rolling resistance
Rolling resistance (FR, also called rolling friction coefficient) can be calculated using the following formula:
FR = CR x FN
The resistance is thus calculated from the rolling resistance coefficient (CR) and the normal force (FN). The normal force depends on the weight on the wheel.
- Calculating the rolling resistance coefficient
The rolling resistance coefficient depends on the material properties of the tyre and the road surface, as well as the dimensions of the tyre (R=radius) and the distance travelled in metres (d). This results in the following formula:
The distance here is the distance of the normal force (FN) to the centre of the wheel and results from deformations during rolling.
- Calculation of the rolling resistance with known rolling resistance coefficient
The rolling friction coefficient does not have to be calculated additionally if tables for friction values of different material pairings are available. Here you can simply look up the value and insert it into the calculation formula.
Why tyres with low rolling resistance are worthwhile
For transport vehicles with an annual mileage of about 50,000 kilometres, savings of several hundred pounds a year can be achieved by using tyres with optimised rolling resistance. But it is also advisable to pay attention to low rolling resistance in manual transport vehicles. This makes transport quicker, easier and more ergonomic.
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