AGV Drive Wheel Rolling Resistance and Energy: Key Data at a Glance

1. When Range Shrinks, Why the Wheels Come Before the Battery

An AGV has been in service for eighteen months. The operator notices that a machine which used to run a full shift on one charge now has to return to its charging station in the afternoon. The instinctive conclusion is battery degradation, so the pack is tested and cells are replaced. After all that work, the capacity loss turns out to be within a reasonable range. The problem was rarely the battery. The vehicle had simply been fighting the floor the whole time.

Battery capacity sets how much energy the vehicle can carry. Rolling resistance sets how quickly that energy is used up. One is storage, the other is consumption rate, and together they define range. After a period of operation, three things change: the tread surface changes shape through wear, the load distribution shifts when the vehicle body is modified, and the floor becomes rougher as coatings age or cleaning methods change. All three push rolling resistance up, and the change is slow enough to escape daily notice until range performance drops visibly.

Looking at the energy flow, the drive motor output splits into roughly three parts: work to overcome rolling resistance and maintain motion, work to overcome air resistance, and energy dissipated in braking. In the low-speed duty of an AGV, air resistance accounts for very little. The portion directly tied to the wheels is the first one, and at low speed and heavy load it is a substantial share of the total traction work, typically more than sixty percent.

This is why a change of tread compound often produces a visible improvement in range, while replacing the battery costs far more. Rolling resistance is largely fixed at the selection stage. Once the vehicle design is frozen and the fleet is in operation, improving it means changing hardware. Building rolling resistance into the selection evaluation is therefore more economical than replacing batteries afterwards.

1.1 The Physical Source of Rolling Resistance: Material Hysteresis, Not Friction

Rolling resistance is often confused with friction between wheel and floor. These describe different phenomena. Sliding friction is relative slip between two contact surfaces. Rolling resistance comes mainly from energy lost inside the material during repeated compression and recovery, known as hysteresis loss.

As a wheel rolls, the part of the tread entering the contact zone is compressed and the part leaving it recovers. An ideal elastic material would release all the energy stored during compression. A real viscoelastic material releases only part of it; the rest is dissipated as heat. That dissipated energy has to be continuously replaced by the motor, and shows up as rolling resistance.

Polyurethane is a classic viscoelastic material. Its hysteresis loss is directly related to molecular structure, crosslink density and compound system. This explains an engineering observation: two polyurethane wheels with the same hardness but different compound systems can have noticeably different rolling resistance. Hardness describes resistance to indentation. Hysteresis loss describes the efficiency of energy storage and return. They are not the same dimension.

The first two items in the table above are directly related to tread selection. The third and fourth fall outside the material itself, but they also raise real energy consumption, and they tend to appear only after the vehicle has run for a long time. That matches the pattern of a range that shortens gradually.

2. Four Factors That Determine Rolling Resistance, and How They Constrain One Another

Rolling resistance cannot be adjusted on its own. It is set jointly by four factors, and changing any one of them shifts the other three. Looking at them separately makes the trade-offs at selection time clearer.

2.1 Factor One: Hysteresis of the Tread Compound

This factor carries a high weight and is one of the hardest to change afterwards. The hysteresis of the polyurethane tread is set by the compound: prepolymer type, chain extender selection and crosslink density are the main variables. A low-hysteresis compound produces less internal loss for the same deformation under load and gives lower rolling resistance. Such compounds also tend to show lower compression set and better dimensional stability.

One point deserves attention: a low-hysteresis compound and a high-wear-resistance compound are not contradictory, but neither are they equivalent. Wear resistance depends mainly on tear strength, cut resistance and surface resilience, while rolling resistance depends on hysteresis loss. In compound design, the two can be partly reconciled through crosslink density and soft-segment structure. That is a task for compound engineering, not something solved by simply raising hardness.

2.2 Factor Two: Tread Hardness

Hardness is the easiest indicator to obtain at selection time, and the easiest to misuse. From the standpoint of rolling resistance, higher hardness usually comes with lower hysteresis loss, because the material resists indentation more strongly, deforms less under the same load, and dissipates less energy in each compression-recovery cycle.

But higher hardness carries three costs. First, floor protection falls: a harder tread adapts less well to fine floor irregularities and uneven joints, which is unwelcome on epoxy floors and clean-room surfaces where surface integrity matters. Second, running noise rises, because a hard material responds more directly to microscopic asperities as it rolls. Third, wear on the floor itself increases, and this is especially visible on wooden floors and some coated surfaces.

This is the real dilemma in wheel selection. The energy advantage of hardness has to be paid for with floor protection and operating experience. Treating hardness as a parameter that can simply be raised is one of the most typical misjudgements in selection.

The hardness grades above follow the common industry breakdown. In practice, the technical data published by the supplier should govern. Note also that within one hardness grade, different compound systems can still show different rolling resistance. Hardness is only the starting point for comparison.

2.3 Factor Three: Deformation Under Load

As load passes through the tread to the floor, the tread layer compresses. The greater the deformation, the more energy is dissipated in each compression-recovery cycle, and the higher the rolling resistance. With the material fixed, deformation is controlled in three ways: raising hardness, increasing wheel diameter, and increasing tread width.

This pattern can be read straight off the specification table. Taking the published specifications of flange-type drive wheels as an example, a 100 mm diameter, 40 mm wide size carries 300 kg per wheel at 4 km/h. When the diameter increases to 300 mm and the width to 60 mm, the per-wheel load capacity rises to 1,100 kg. As load capacity increases, the deformation per unit load actually falls. Large diameters therefore tend to offer both a better load margin and lower rolling resistance in heavy-duty applications.

Large diameters come at a price, however. A larger wheel changes the ground clearance of the vehicle body, so the drive unit mounting interface has to be re-matched. The wheel itself also becomes heavier, which raises inertia in steering and braking. These are constraints that must be considered together in selection; load capacity and resistance cannot be the only criteria.

2.4 Factor Four: Floor Roughness and Friction Conditions

The same wheel behaves very differently on different floors. Greater floor roughness makes the tread press into and out of microscopic features more frequently, so contact area and deformation frequency rise together and rolling resistance increases. Field experience shows that moving the same vehicle from a polished concrete floor to a worn epoxy floor can change energy consumption per kilometre by more than ten percent.

Floor condition affects energy consumption through a second route as well: the coefficient of friction. Rolling resistance and the sliding friction coefficient are not the same quantity, but both arise from material interaction at the contact interface. Where oil, a water film or cleaning-agent residue is present, the friction coefficient drops, the wheel is more prone to micro-slip, and part of the traction work is wasted on slipping. That shows up as higher energy consumption and poorer positioning accuracy.

The relationship among these four factors can be summarised in one sentence: the material sets the baseline ceiling, hardness sets the direction of the trade-off, deformation under load sets the working point, and the floor sets the actual outcome. These four layers constrain each other in sequence, rather than being independent boxes to tick. Once the material system is fixed, rolling resistance has a ceiling that cannot be crossed. Within that ceiling, hardness sets the direction: moving towards low resistance means conceding floor protection and noise. Deformation under load then turns that direction into a specific working point, since the same hardness grade deforms differently under different loads. Floor condition is the final correction: the same wheel on polished concrete and on a dusting old floor will show clearly different rolling resistance. If these four layers are identified in order at selection time, rolling resistance no longer has to be judged by feel.

3. Turning Rolling Resistance into Electricity Cost: A Five-Step Calculation Method

The raw value of rolling resistance means little to purchasing and operations staff. What carries decision value is the energy consumption and cost behind it. The five steps below give a formula and a worked example for each, so readers can substitute their own operating parameters and recalculate.

3.1 Step One: List the Five Basic Operating Parameters

The inputs are: total vehicle mass, operating speed, daily operating time or distance, number of drive wheels and load per wheel, and a floor condition factor. These five parameters define every subsequent input. Where measured floor data is unavailable, the floor condition factor can be estimated conservatively using the table in the previous section.

3.2 Step Two: Calculate the Load on a Single Wheel

The normal load on one wheel is distributed from the total vehicle mass according to the number of wheels and a load distribution factor, expressed as F = m × g ÷ n × k. Here m is total vehicle mass, g is 9.8 m/s², n is the number of load-bearing wheels, and k is the load distribution unevenness factor. For a four-wheel AGV with fairly even load distribution, k is usually taken as 1.1 to 1.2. Where there is significant off-centre loading, k must be raised accordingly.

3.3 Step Three: Estimate Rolling Resistance

Rolling resistance equals normal load multiplied by the rolling resistance coefficient: Fr = F × Crr. The coefficient is the critical input at this stage, and it results from the combined effect of material, hardness, load and floor condition. Where the manufacturer has no measured data, polyurethane wheels can be taken in the range 0.008 to 0.025. The basis for choosing within that range is hardness grade and floor roughness: a hard tread on a smooth floor takes the lower end, a soft tread on a rough floor takes the upper end.

3.4 Step Four: Convert to Drive Motor Output Work

The work the drive wheel must deliver equals rolling resistance multiplied by distance travelled: W = Fr × L. Note that this is mechanical work. The complete chain from battery to drive wheel also passes through motor efficiency, gearbox efficiency and drive controller conversion losses. Overall drivetrain efficiency is typically between 0.7 and 0.85. Dividing the mechanical work by drivetrain efficiency gives the electrical energy drawn from the battery.

3.5 Step Five: Compare Energy Consumption per Kilometre Between Options

Substituting two tread options into the same set of formulas gives the difference in energy consumption per kilometre. Multiplying that by annual distance travelled and the electricity tariff gives the annual difference in energy cost. That figure is the number worth weighing at selection time.

3.6 A Worked Example: How Large Is the Energy Gap Between Two Tread Grades

The following example uses clearly stated assumptions to demonstrate the calculation logic. Total vehicle mass is 1,500 kg with four load-bearing wheels, the load distribution factor is 1.15, daily distance is 20 km over 300 operating days, the floor is epoxy coated, drivetrain efficiency is taken as 0.8, and the electricity tariff is estimated at 1.0 CNY per kWh on an industrial rate.

Three points need emphasis about this calculation. First, the rolling resistance coefficients in the table are example values used to demonstrate the method. They do not represent the measured performance of any specific product; actual figures should come from supplier test data or field measurement. Second, the energy gap shows up in both electricity cost and range. In this example the annual cost difference of roughly 1,141 CNY may not look large on its own, but at an industrial tariff of 1.0 CNY per kWh it is a meaningful line item once a fleet is considered rather than a single vehicle. Third, this example does not include the difference in replacement cost arising from different tread wear cycles, which should be factored in during real selection.

Used in reverse, the same calculation answers another question: is it always worthwhile to choose a hard tread in pursuit of low rolling resistance? Where the vehicle is light, the annual distance is short, and the floor is sensitive, the absolute energy saving shrinks noticeably while the cost in floor protection may be larger. The value of the calculation is precisely that it turns this kind of trade-off from a qualitative judgement into a quantitative one.

3.7 Five-Step Calculation Formulas at a Glance

For field use, the formulas, value conventions and cautions for all five steps are collected below, ready to be applied directly to an organisation own data.

One precondition applies when using this table. The rolling resistance coefficient is the most uncertain input in the whole calculation, because it is affected simultaneously by material, hardness, load and floor. Where measured manufacturer data is unavailable, taking a value from the range and applying a conservative factor is closer to reality than plugging in a single precise number.

4. Five Details That Are Easy to Get Wrong

4.1 Using Hardness as a Substitute for Rolling Resistance

Hardness is one of the factors influencing rolling resistance, but it is not a proxy for it. Two polyurethane wheels both rated 93 Shore A can show clearly different hysteresis loss if their compound systems differ. When requesting data from a supplier, ask specifically for measured rolling resistance or hysteresis loss, rather than relying on the hardness marking alone.

4.2 Ignoring the Twin Effect of Speed on Load Capacity and Resistance

Load capacity must always be quoted together with a speed condition. Taking published specifications as an example, the same drive wheel size carries clearly more at 4 km/h than at 10 km/h. A load rating without a speed condition has no comparative meaning, and the same applies to rolling resistance, because higher speed increases the number of deformation cycles per unit time.

4.3 Confusing Rolling Resistance with Starting Resistance

Moving a vehicle from rest requires overcoming static friction, and that quantity is usually larger than rolling resistance. In AGV applications with frequent starts and stops, the cumulative effect of starting resistance cannot be ignored. Calculating on rolling resistance alone will underestimate real energy consumption. When evaluating a vehicle, tell the supplier the start-stop frequency so the right compound orientation can be recommended.

4.4 Failing to Account for Temperature-Related Drift

The mechanical properties of polyurethane vary with temperature. The published operating range is -30°C to +70°C with short-term exposure to +90°C, and the data also notes that load capacity decreases above +40°C. In cold storage, the material hardens and both hysteresis loss and compliance change. In a high-temperature workshop, the calculation must be redone against the reduced load capacity. Rolling resistance should always be calculated at the actual working temperature of the application.

4.5 Overlooking Batch-to-Batch Variance

Calculating rolling resistance assumes stable parameters. In real operation, if wheel diameters differ between batches, two wheels on the same axle turn at different speeds and generate a continuous correcting action that consumes extra energy. This kind of loss is invisible on a single wheel, but at vehicle level it steadily raises energy consumption. Dimensional consistency in volume deliveries is therefore not only a quality issue; it is also an energy issue.

5. The Order of Judgement When Choosing a Tread for a Given Duty

The analysis so far can be arranged into an order of judgement that can be followed step by step. Working through it in sequence usually avoids any major deviation in selection.

These five orders are not independent; the conclusion of each constrains the options available at the next. In a clean room with a sensitive floor, for instance, the hardness ceiling is pushed down, so the same load capacity can only be reached by increasing wheel diameter or tread width, and the choice of diameter is in turn limited by vehicle structure. Selection is a process of progressive convergence, not a checklist of independent boxes.

6. The HANKE Approach: Managing Rolling Resistance as a Process Indicator

Rolling resistance is a parameter that is difficult to remedy after the fact but controllable beforehand. Once a vehicle design is frozen and in operation, using a tread change to cut energy consumption costs disassembly time and downtime. If instead the compound selection, moulding process and finished-product inspection are all controlled against the duty target, consistency at delivery becomes traceable. HANKE has built several key links in this chain into documented process controls.

6.1 A Premise: Resistance Differences Come from Compound and Process, Not Hardness Alone

In HANKE engineering practice, one hardness grade does not mean one compound. The 75 ± 3 Shore A grade, for example, is positioned for floor protection and low noise, with rolling resistance and wear performance both at a good level. The 93 ± 3 Shore A grade leans towards wear resistance and low resistance, with somewhat reduced floor protection. These two grades correspond to two tread systems, HANKE Eamflex 93A and HANKE Saxflex 75A, and are matched to the duty orientation at selection time. In this material line, the wheel core, bonding process and finished dimensions are all held against the same duty target, so that the resistance actually delivered matches the resistance calculated at the selection stage.

6.2 Four Control Gates

Control starts with incoming wheel cores. The core material can be selected as 45# steel, cast iron, die-cast aluminium alloy or stainless steel depending on duty, with surface treatments including painting, phosphating, zinc plating and Dacromet. The condition of incoming cores directly affects subsequent bond quality. The three bonding processes form the second gate: shot blasting removes the surface oxide layer, adhesive spraying controls adhesive thickness and uniformity, and dynamic pressure control during casting ensures a dense adhesive layer. The third gate is moulding and finish turning, where critical dimensions are verified by measurement after turning; dimensional consistency at this stage directly governs the additional resistance of multiple wheels running on the same axle. The fourth gate is finished-product inspection, where hardness, critical dimensions and appearance are recorded by batch.

6.3 What the Customer Can Receive

Turning trust into verifiable actions is more meaningful than any adjective. HANKE process records are kept by batch precisely so that a customer can trace any single wheel back to the parameters under which it was made. The HANKE inspection stage is equipped with CHOTEST coordinate measuring equipment, and critical dimensions are sampled and recorded by batch. The speed conditions marked alongside load capacity in the product specification tables (4 km/h and 10 km/h) also provide the necessary input for energy calculations. At the selection stage, customers can request batch critical-dimension inspection records, hardness inspection records, and a duty evaluation with configuration recommendation based on total vehicle mass, operating speed, floor condition and working temperature.

6.4 One Thing That Needs to Be Said Clearly

No manufacturing system should promise that deviation will never occur. That is neither realistic nor consistent with engineering practice. What deserves more attention is something else: whether changes in resistance are kept within a range that is predictable, verifiable and traceable. When a single unit performs abnormally, can the inspection records for that batch be retrieved, can the process step be identified, can the parameter that drifted be named, and can corrective action be given? That is the substance of capability management.

In automotive production line applications, the specification used on the Fujian Benz line is a 250 mm diameter, 80 mm wide drive wheel, with a per-wheel load in the two-tonne class, using the 95 Shore A grade together with HANKE Eamflex 93A tread system, and a record of 48 months without after-sales issues, with service life approximately 30% longer than the comparable reference over the same period. What such a record demonstrates is not that problems never occur, but that long-term stability is achievable when resistance, precision and consistency are managed continuously as process indicators.

7. Frequently Asked Questions

Q1: Lower rolling resistance is always better, right?

No. Low rolling resistance usually means a harder tread, at the cost of reduced floor protection and higher running noise, which can wear epoxy floors, wooden floors and clean-room surfaces. The goal of selection is to find the balance that matches the application across load capacity, floor protection, noise and energy consumption, not to push one indicator to an extreme.

Q2: Do harder wheels always use less electricity?

Where the material system is the same, higher hardness usually comes with lower hysteresis loss and improved energy performance. But where compound systems differ, it is entirely possible for two wheels of the same hardness to show different rolling resistance. Energy performance should be judged on measured rolling resistance or hysteresis loss, not on the hardness marking alone.

Q3: Are rolling resistance and wear resistance the same indicator?

No. Rolling resistance depends on the hysteresis loss of the material. Wear resistance depends on tear strength, cut resistance and surface resilience. Both must be considered in compound design, and they can be partly reconciled through crosslink density and soft-segment structure. That falls within the scope of compound engineering.

Q4: AGV range has dropped. How do I tell whether it is the battery or the wheels?

Start with a cross-check: measure energy consumption per kilometre on the same route under the same load. If it is clearly higher than the figure when the vehicle was new, while battery capacity loss is within a reasonable range, the change is more likely on the wheel side. Common causes include tread wear altering hardness and the actual contact condition, diameter wear producing mismatched wheel speeds on the same axle, and floor coating aging raising roughness.

Q5: Does changing the tread really improve range noticeably?

It depends on the duty. In heavy-load, long-distance applications on hardened floors, the difference in energy consumption per kilometre between options is significant and the improvement in range is easy to feel. In light-load, short-distance applications with frequent stops, the absolute difference in energy is smaller, and attention should go to starting resistance and floor protection rather than low rolling resistance alone.

Q6: Is rolling resistance in cold storage the same as at ambient temperature?

No. The mechanical properties of polyurethane vary with temperature. The marked operating range is -30°C to +70°C, and load capacity decreases above +40°C. At low temperature the material hardens, and both compliance and hysteresis characteristics change. Energy calculations should be based on the actual working temperature of the application, with the load margin adjusted accordingly.

Q7: Does wheel diameter affect rolling resistance?

Yes. Under the same load, a larger diameter produces relatively less compression of the tread, so the rolling resistance coefficient falls. This is one reason heavy-duty applications tend to favour larger diameters. However, a larger diameter changes vehicle ground clearance and affects the drive unit mounting interface, so it must be evaluated together with the overall vehicle structure.

Q8: How can I judge whether a supplier rolling resistance data is reliable?

Look at four things: whether measured rolling resistance or hysteresis loss data is provided rather than a hardness marking alone; whether load capacity is quoted with a speed condition; whether critical dimensions and hardness have batch inspection records; and whether the supplier can evaluate your duty and recommend a configuration. All four of these can be requested or provided.

8. Conclusions and Recommendations

AGV range problems are rarely caused by a single factor, but rolling resistance is the one most easily overlooked and the one most worth calculating first. The key points of this article reduce to five recommendations.

First, put rolling resistance on the selection evaluation list. It is not something to worry about only in operation; it is largely fixed at the selection stage, and the cost of optimising it later is clearly higher.

Second, use the five-step method to convert resistance into energy and cost. The rolling resistance coefficient itself carries no decision value. Energy consumption per kilometre and the annual electricity cost difference are the figures that can be put on the table for comparison.

Third, do not use hardness as a substitute for rolling resistance and wear performance. Hardness is the starting point of selection, not the end point. Differences between compound systems at the same hardness have to be confirmed with measured data.

Fourth, include speed and temperature conditions in the calculation. A load rating without a speed condition has no comparative meaning, and both material performance and resistance vary with working temperature. Cold storage and high-temperature workshops need separate evaluations.

Fifth, factor batch consistency and supplier capability into the decision. Additional resistance when multiple wheels run on the same axle comes from dimensional differences, and long-term energy stability depends on process control capability, which can be verified by requesting batch inspection records.

For teams currently selecting an AGV travel system, or looking for the cause of a range problem, the recommendation is to first run the calculation on your own data using the method set out here, then compare the result against the data of candidate options. If support during the calculation stage would be useful, the HANKE technical team can carry out a duty evaluation based on total vehicle mass, operating speed, floor condition and working temperature, and validate the result through a small-batch trial installation.

About HANKE

HANKE (Wenzhou) Polyurethane Technology Co., Ltd. traces its technical origins to a polyurethane elastomer casting equipment development team founded in 1989, with more than 35 years of focus on the polyurethane industry. The company holds 52 technical achievements covering polyurethane compound development, wheel hub structural design, mould engineering and product appearance, forming a complete technical system. Its products are validated over the long term on the production lines of leading companies including Mercedes-Benz, Land Rover, Changan Automobile, Geely, Kinco Electric and Tennant.

HANKE manufacturing covers the full chain from shot blasting, adhesive spraying and casting through to incoming and finished-product inspection. CHOTEST coordinate measuring machines at 1 micrometre precision are used to fully inspect the critical dimensions of every batch of wheels. Carrying the mission of making the movement of people and goods safer, HANKE is committed to becoming an influential roller wheel manufacturer in China intelligent logistics sector.

5. The Order of Judgement When Choosing a Tread for a Given Duty

The analysis so far can be arranged into an order of judgement that can be followed step by step. Working through it in sequence usually avoids any major deviation in selection.

These five orders are not independent; the conclusion of each constrains the options available at the next. In a clean room with a sensitive floor, for instance, the hardness ceiling is pushed down, so the same load capacity can only be reached by increasing wheel diameter or tread width, and the choice of diameter is in turn limited by vehicle structure. Selection is a process of progressive convergence, not a checklist of independent boxes.

6. The HANKE Approach: Managing Rolling Resistance as a Process Indicator

Rolling resistance is a parameter that is difficult to remedy after the fact but controllable beforehand. Once a vehicle design is frozen and in operation, using a tread change to cut energy consumption costs disassembly time and downtime. If instead the compound selection, moulding process and finished-product inspection are all controlled against the duty target, consistency at delivery becomes traceable. HANKE has built several key links in this chain into documented process controls.

6.1 A Premise: Resistance Differences Come from Compound and Process, Not Hardness Alone

In HANKE engineering practice, one hardness grade does not mean one compound. The 75 ± 3 Shore A grade, for example, is positioned for floor protection and low noise, with rolling resistance and wear performance both at a good level. The 93 ± 3 Shore A grade leans towards wear resistance and low resistance, with somewhat reduced floor protection. These two grades correspond to two tread systems, HANKE Eamflex 93A and HANKE Saxflex 75A, and are matched to the duty orientation at selection time. In this material line, the wheel core, bonding process and finished dimensions are all held against the same duty target, so that the resistance actually delivered matches the resistance calculated at the selection stage.

6.2 Four Control Gates

Control starts with incoming wheel cores. The core material can be selected as 45# steel, cast iron, die-cast aluminium alloy or stainless steel depending on duty, with surface treatments including painting, phosphating, zinc plating and Dacromet. The condition of incoming cores directly affects subsequent bond quality. The three bonding processes form the second gate: shot blasting removes the surface oxide layer, adhesive spraying controls adhesive thickness and uniformity, and dynamic pressure control during casting ensures a dense adhesive layer. The third gate is moulding and finish turning, where critical dimensions are verified by measurement after turning; dimensional consistency at this stage directly governs the additional resistance of multiple wheels running on the same axle. The fourth gate is finished-product inspection, where hardness, critical dimensions and appearance are recorded by batch.

6.3 What the Customer Can Receive

Turning trust into verifiable actions is more meaningful than any adjective. HANKE process records are kept by batch precisely so that a customer can trace any single wheel back to the parameters under which it was made. The HANKE inspection stage is equipped with CHOTEST coordinate measuring equipment, and critical dimensions are sampled and recorded by batch. The speed conditions marked alongside load capacity in the product specification tables (4 km/h and 10 km/h) also provide the necessary input for energy calculations. At the selection stage, customers can request batch critical-dimension inspection records, hardness inspection records, and a duty evaluation with configuration recommendation based on total vehicle mass, operating speed, floor condition and working temperature.

6.4 One Thing That Needs to Be Said Clearly

No manufacturing system should promise that deviation will never occur. That is neither realistic nor consistent with engineering practice. What deserves more attention is something else: whether changes in resistance are kept within a range that is predictable, verifiable and traceable. When a single unit performs abnormally, can the inspection records for that batch be retrieved, can the process step be identified, can the parameter that drifted be named, and can corrective action be given? That is the substance of capability management.

In automotive production line applications, the specification used on the Fujian Benz line is a 250 mm diameter, 80 mm wide drive wheel, with a per-wheel load in the two-tonne class, using the 95 Shore A grade together with HANKE Eamflex 93A tread system, and a record of 48 months without after-sales issues, with service life approximately 30% longer than the comparable reference over the same period. What such a record demonstrates is not that problems never occur, but that long-term stability is achievable when resistance, precision and consistency are managed continuously as process indicators.

7. Frequently Asked Questions

Q1: Lower rolling resistance is always better, right?

No. Low rolling resistance usually means a harder tread, at the cost of reduced floor protection and higher running noise, which can wear epoxy floors, wooden floors and clean-room surfaces. The goal of selection is to find the balance that matches the application across load capacity, floor protection, noise and energy consumption, not to push one indicator to an extreme.

Q2: Do harder wheels always use less electricity?

Where the material system is the same, higher hardness usually comes with lower hysteresis loss and improved energy performance. But where compound systems differ, it is entirely possible for two wheels of the same hardness to show different rolling resistance. Energy performance should be judged on measured rolling resistance or hysteresis loss, not on the hardness marking alone.

Q3: Are rolling resistance and wear resistance the same indicator?

No. Rolling resistance depends on the hysteresis loss of the material. Wear resistance depends on tear strength, cut resistance and surface resilience. Both must be considered in compound design, and they can be partly reconciled through crosslink density and soft-segment structure. That falls within the scope of compound engineering.

Q4: AGV range has dropped. How do I tell whether it is the battery or the wheels?

Start with a cross-check: measure energy consumption per kilometre on the same route under the same load. If it is clearly higher than the figure when the vehicle was new, while battery capacity loss is within a reasonable range, the change is more likely on the wheel side. Common causes include tread wear altering hardness and the actual contact condition, diameter wear producing mismatched wheel speeds on the same axle, and floor coating aging raising roughness.

Q5: Does changing the tread really improve range noticeably?

It depends on the duty. In heavy-load, long-distance applications on hardened floors, the difference in energy consumption per kilometre between options is significant and the improvement in range is easy to feel. In light-load, short-distance applications with frequent stops, the absolute difference in energy is smaller, and attention should go to starting resistance and floor protection rather than low rolling resistance alone.

Q6: Is rolling resistance in cold storage the same as at ambient temperature?

No. The mechanical properties of polyurethane vary with temperature. The marked operating range is -30°C to +70°C, and load capacity decreases above +40°C. At low temperature the material hardens, and both compliance and hysteresis characteristics change. Energy calculations should be based on the actual working temperature of the application, with the load margin adjusted accordingly.

Q7: Does wheel diameter affect rolling resistance?

Yes. Under the same load, a larger diameter produces relatively less compression of the tread, so the rolling resistance coefficient falls. This is one reason heavy-duty applications tend to favour larger diameters. However, a larger diameter changes vehicle ground clearance and affects the drive unit mounting interface, so it must be evaluated together with the overall vehicle structure.

Q8: How can I judge whether a supplier rolling resistance data is reliable?

Look at four things: whether measured rolling resistance or hysteresis loss data is provided rather than a hardness marking alone; whether load capacity is quoted with a speed condition; whether critical dimensions and hardness have batch inspection records; and whether the supplier can evaluate your duty and recommend a configuration. All four of these can be requested or provided.

8. Conclusions and Recommendations

AGV range problems are rarely caused by a single factor, but rolling resistance is the one most easily overlooked and the one most worth calculating first. The key points of this article reduce to five recommendations.

First, put rolling resistance on the selection evaluation list. It is not something to worry about only in operation; it is largely fixed at the selection stage, and the cost of optimising it later is clearly higher.

Second, use the five-step method to convert resistance into energy and cost. The rolling resistance coefficient itself carries no decision value. Energy consumption per kilometre and the annual electricity cost difference are the figures that can be put on the table for comparison.

Third, do not use hardness as a substitute for rolling resistance and wear performance. Hardness is the starting point of selection, not the end point. Differences between compound systems at the same hardness have to be confirmed with measured data.

Fourth, include speed and temperature conditions in the calculation. A load rating without a speed condition has no comparative meaning, and both material performance and resistance vary with working temperature. Cold storage and high-temperature workshops need separate evaluations.

Fifth, factor batch consistency and supplier capability into the decision. Additional resistance when multiple wheels run on the same axle comes from dimensional differences, and long-term energy stability depends on process control capability, which can be verified by requesting batch inspection records.

For teams currently selecting an AGV travel system, or looking for the cause of a range problem, the recommendation is to first run the calculation on your own data using the method set out here, then compare the result against the data of candidate options. If support during the calculation stage would be useful, the HANKE technical team can carry out a duty evaluation based on total vehicle mass, operating speed, floor condition and working temperature, and validate the result through a small-batch trial installation.