otraco-web-publications-maximising-tyre-life-september-2002.pdf

8/11/2019 otraco-web-publications-maximising-tyre-life-september-2002.pdf

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O T R A C O (International ) Pty Ltd

Ty r e S e l e c t i o n , U s e a n d O p e r a t i o n a lI s s u e s t o M a x i m i s e Ty r e L i f e

B y : C . A . W o o d m a n & A . T . C u t l e r ,O t r a c o ( I n t e r n a t i o n a l ) P t y L t d .

OVERVIEW

yres are typically one of themajor costs incurred byMining and Quarrying

operations. However, the selection,maintenance and operation of tyresis one operational aspect which isnot normally adequately addressed,given its overall impact on

performance.The correct selection of tyres candramatically impact on the overallcost of any earthmoving operation,as tyres can account for between25% to 40% of these costs. Thispaper will examine the selectionprocess for earthmover tyres, alongwith operational practices tomaximise tyre life.

TYRE SELECTION

As with most selection criteria, tyreselection is a compromise. Thereare many mutually exclusive criteriawhich need to be balanced againstone-another to achieve an optimumtyre life and cost.

Tyres are exposed to a variety ofoperating conditions includingoverloading, rock damage and heatbuild-up within the tyre from flexing.

All of these operating conditionscreate different loads that the tyremust withstand. However, a tyresability to withstand one of these

conditions lessens its ability towithstand the other two conditions.Therefore a major part of the tyreselection process will include anassessment of the operatingconditions which the tyre will face.

It is essential that the selection taskis carried out by professionals whowill understand the tasks required ofyour tyres and recommend only theoptimum tyre for the task. Thisrecommendation should be basedon sound assessment techniques, toachieve the minimum operational

costs, backed up with practicalexperience.

The design and operation of minesand quarries is a continually evolving

process. The nature of the evolutionis dependant on the type of mine,type of material being reclaimed andthe actual geology of the operationitself, along with the fixed plantinfrastructure locations. Therefore,tyre selection should also be re-evaluated as operational changesoccur.

Tyres are normally rated in terms oftheir heat resistance (ability toperform work), cut and abrasionresistance (resistance to damage)and their traction characteristics(usually a function of tyreconstruction and tread pattern). Themethod of selection to determine aparticular tyres suitability, for agiven operation, is usually based onthe operational conditions at theparticular mine and the tyres TonneKilometre per Hour rating (TKPH).

As a tyre rotates, the deflection ofthe tyre causes the tyres structureto flex. As the tyre rotates throughthe tyres contact point, the tyresstructure compresses then releasesto its original shape. Due to the in-elastic properties of the tyresstructure, some of the energyintroduced through the flexing of thestructure is retained as heat. If the

cycle of flexing and release is rapid,heat builds up within the tyre.

The critical temperature for a tyrevaries between constructionmethods. Figure 1 shows thestatistical probability of a tyreundergoing a heat separationrelative to internal temperature. If theinternal temperature of a tyre shouldrise above the critical temperature(normally taken to be 97 C for radial

tyres and 109C for bias tyres), thenthe probability of heat related

failures due to chemical andphysical changes within the tyreincreases.

The two main operational influenceson tyre heat build-up are:

Speed - as this affects thenumber of cycles per unit time.

Load - as this affects theamplitude of tyre deflection, henceenergy transferred.

T

Relationship Between Tyre Temperature and HeatDamage

0%10%20%30%40%50%60%70%80%

90%100%

90 110 130 150 170 190

Tyre Temperature( Degrees C)

S t a t i s

t i c a

l P r o

b a

b i l i t y o

f H e a

t

S e p a r a

t i o n

D a m a g e

Radial Tyres Bias Ply Tyres

Figure 1 - Tyre Temperature versus Heat Damage


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2 O T R A C O (International) Pty Ltd - Tyre Selection, Use and Operational Issu es to Maximi se Tyre Life

Figure 2 - Tyre ReferenceDimensions

Figure 2, above shows the mostcommonly used referencedimensions for earthmover tyres.

Construction

Types of TyresFor earthmoving applications, thereare two main types of tyres. Theseare radial and bias-ply tyres. This

excludes solid tyres or other specialtyres such as steel wheeled ortracked vehicles.

The development of radial tyres hasbeen rapid. In 1960, radial tyrescomprised only two percent of alllight vehicle and earthmover tyres inoperation world wide. Onemanufacturer, Michelin, accountedfor approximately 90% of thesetyres.

During the 1960-70s the use of lightvehicle radial tyres becamewidespread, firstly on passengervehicles, then on light trucks andfinally on heavy road trucks. By 1980radials comprised the majority oflight vehicle tyres in service, but only5 percent of earthmover tyres.

Since then radial tyre acceptance bythe mining industry has increaseddramatically. The proportion of radialearthmover tyres rose to 65 percentby 1990 and is continuing to grow.

A parallel development over thesame period was the reduction in thenumber of major earthmover tyre

manufacturers from eight to three.Bridgestone, Goodyear and Michelinaccount for most of the radialearthmover tyres being producedtoday.

Bias-Ply Construction

Figure 3 below shows a typical bias-ply tyre construction.

Figure 3 - Bias-Ply Tyre Construction

A bias-ply tyre has a bulky casingcomposed of many criss-crossednylon layers as shown in Figures 3and 4. Tyre flexing causesdeformation of the casing and hour-glassing of the section of tread incontact with the ground, as shown inFigure 4. This results in tread squirmand uneven contact pressure acrossthe footprint area. Tyre flexing alsocauses scissoring of adjoining plylayers, increasing casing stress andheat build-up.

Figure 4 - Bias-Ply tyre treadpatterns (loaded and unloaded)

Radial Ply Construction

Figure 5 below shows a typical radialtyre construction.

Figure 5 - Radial Tyre Construction

A radial tyre has a thin casing

composed of a single radiallyorientated steel ply layer which iscontained by severalcircumferentially aligned steel treadbelts. Tyre flexing is absorbed by theradial casing ply with littledeformation of the tread; the steelbelts act like a tank track providinguniform ground contact pressure.The radials thin casing alsogenerates less heat and stressmaking it better suited to high speedapplications and more amenable torepairs, especially in the side wallarea.

Figure 6 - Radial tyre tread patterns(loaded and unloaded)

Radial tyres have severaladvantages over bias-ply tyres.These are:

Radials commonly have a higherTKPH rating than the same sizebias tyre.

Heat generation in radial tyres islower due to construction and thethinner casing required.


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3 O T R A C O (International) Pty Ltd - Tyre Selection, Use and Operational Issu es to Maximi se Tyre Life The tread of a radial tyre is not

affected by the side wall flexing,creating less deformation of thetread, leading to reduced treadwear.(Figures 4 and 6 highlight this.)

Higher grip levels. Lower fuel consumption through

reduced rolling resistance andfriction.

Smoother ride because of thereduced side wall stiffness.

Better flotation characteristics.

Steel belts that provide additionalresistance to tread damage.

Higher repair success rate.

Once the choice between a radialand bias-ply tyre has been finalised,the detailed analysis begins. Areasthat have to be examined include,type of road surface, condition ofroad, road profile, weatherconditions, traction requirements,previous failure history if availableand type of material beingtransported.

PatternThe pattern of the tyre is normallyrelated to the type of operation thatthe tyre will be utilised in. Typicallytyre manufacturers provide varyingpatterns varying from traction to rockpatterns.

As the name suggests, a tractionpattern tyre is designed to maximiseavailable traction. This type of tyreis usually characterised by a largeopen tread style, with manyindividual tread lugs.

A rock pattern normally has fewerindividual lugs. The reduced openarea prevents rocks being capturedin the tread voids and cutting into thetyre.

As a general rule, the higher therock protection the higher the actuallevel of reinforcement and protectionof the tyre. Conversely the higherthe rock protection the lower thetyres traction, adhesion andoperating speed limits.

Therefore it is essential that theoptimum compromise be obtainedbetween traction and rockresistance. Traction tyres operatingon rocky surfaces will wear quicker

than rock type tyres. Operator safetycan be jeopardised if rock tyres areused in areas requiring traction. Ifany tyre is subjected to excessive

wheel slip or spin, wear rates will bedramatically increased.

Ply Rating(where applicable)For bias-ply tyres, the load carryingcapability of the tyre is normallyproportional to the ply rating. Theply rating is the strength of the tyreexpressed against the equivalentnumber of cotton plys.

Bias-ply tyres were originallymanufactured utilising cotton for theply weave. To assist in comparisonsand understanding, when newermaterials such as nylon etc wereintroduced, tyre ratings weremeasured against a standardcotton construction tyre, rather thanthe actual number of plys present.

The higher the number of plys, thehigher the load carrying capability ofthe tyre.

For radial tyres, a star rating (H) isutilised. Radial tyres are given a starrating from one to three (mostearthmover applications arenormally one or two star).Manufacturers may publishconversion tables for star to ply

ratings, but it is better to use theload inflation tables to determine themaximum loads for each tyre.

By knowing the maximum tyre load(preferably from weighbridgeanalysis), the tyre with the correctload carrying capability can bedetermined.

Tread Depth and TyreCompoundThe tyre compound refers to theactual type of rubber compound and

tyre construction used.Manufacturers can vary the stiffnessand hardness of the structure andthe rubber to achieve optimal tyrecharacteristics.

Tyres are normally available in threetypes of compound, cut resistant,heat resistant and ultra heatresistant. The choice of which ispreferable is based on failurehistory, operating conditions andTonne Kilometre Rating (TKPH).

Table 1 - Bridgestone constructions

1 Steel breaker construction 2 Side steel breaker construction= Bias-ply tyres only

Service BSCodeNo.

Structure

Earthmover 1A2A3A

StandardCut-resistantHeat-resistant

Grader 1A2A StandardCut Resistant

Loader&Dozer

2A2V= 2Z=

Cut-resistantSp ecial (TypeV)1 Special (Type Z) 2


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4 O T R A C O (International) Pty Ltd - Tyre Selection, Use and Operational Issu es to Maximi se Tyre Life Tables one through to three give thevarying construction and compoundtyre types available fromBridgestone, Goodyear and Michelin

Table 4 gives the Tyre and Rim Association (TRA) Off-the-road tyrenomenclature and type of serviceapplicable.

Where the TRA table calls for deeptread tyre, the tread depth is 150%of a standard tread depth tyre andan extra deep tread tyre tread depthis 250% of a standard depth tyre.

From Table 4, there are choices that

have to be made as to the type oftyre performance required. Thechoices involve a trade-off betweenheat resistance and rock / cutresistance. The trade-off betweenheat resistance and cut resistanceoccurs as carcass strength andrubber hardness vary between thetwo types of tyres. This variance inhardness changes the amount ofenergy generated per revolution ofthe tyre.

Approximately 80% of the cost ofmanufacturing an earthmover tyre is

expended in the casing. Theremaining 20% is expended in thetread. Therefore, to extend a tyreslife, one method is to increase thetread depth. Based on the 20% costof the tread, a 50% increase in treaddepth could be achieved for only anapproximate 10% increase in thetyre purchase price. If this extra 50%of tread can be utilised in service,this would dramatically decrease thetyres cost per kilometre or cost perhour.

The disadvantage of thicker tread is

(due to the greater amount ofmaterial utilised) heat is notdissipated as quickly. A thicker treadtyre usually carries a lower TKPHrating than a standard tread depthtyre for this reason. The actual depthof tread chosen will normally dependon the past performance of tyres onsite, or practical experience fromsimilar operations elsewhere.

For example, if standard tread tyresare failing from rock damage at 50%worn, an option would be to extendthe life of the standard tread tyres by

preventing rock damage as opposedto purchasing deep tread tyres. Thisis due to the fact that the tread depthwill only protect the tyre so much. Ifmajor rock damage is occurring,even having 50% more tread depthwill not protect the tyre, thereforethis extra tread is wasted.

This is a simplistic example howeverand there may be other factorswhich have to be accounted for atvarying sites. The option of utilisinga deep tread tyre should beexamined due to the potential

savings available.

VEHICLE TYPE TRA CODENUMBER

TREAD TYPE M AXIMUM S PEED DISTANCE (KPH ) (ONE WAY )

Earthmover

Dump trucks,scrapers,

articulateddump trucks.

E-1

E-2E-3

E-4

E-7

Rib

TractionRock

Rock Deep Tread

Flotation

65

6565

65

65

4.0 km

4.0 km4.0 km

4.0 km

4.0 km

GradersG-1

G-2

G-3

G4

Rib

Traction

Rock

Rock Deep Tread

40

40

40

40

Unlimited

Unlimited

Unlimited

UnlimitedShovels,Loaders,

Bulldozers,Load-Haul

Dump Trucks

L-2

L-3

L-4

L-4S

L-5

L-5S

Traction

Rock

Rock Deep Tread

Smooth Deep Tread

Rock Extra-DeepTread

Smooth Extra Deep

Tread

10

10

10

10

10

10

75 m

75 m

75 m

75 m

75 m

75 m

CompoundDescription

CompoundCode

ConstructionDescription

ConstructionCode

Heat Resistant (HR) 2 Standard S

Standard AbrasionResistant (AR)

4 Steel Breakers J

Ultra AbrasionResistant (UAR)

6 HeavyUndertread

U

Table 2 - Compound and Construction Types for Goodyear Tyres

Tread DepthCode

Relative TreadDepth

ConstructionCode

Construction Type

N 100% type A Rock and abrasionresistant

D1 150% type B Heat resistant

D2 250% type C High speed, long haul

Table 3 - Michelin Tread Depth and Construction Codes

Table 4 - TRA Classification of Tyres for Earthmoving


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5 O T R A C O (International) Pty Ltd - Tyre Selection, Use and Operational Issu es to Maximi se Tyre Life Tonne Kilometre per HourRating (TKPH)

As a basis of determining thesuitability of a tyre for a givenoperation, the final check is theTonne Kilometre per Hour (TKPH)rating. At its most simplest form, theTKPH rating of a site is a measure ofthe earthmovers average speedmultiplied by the average tyre load.This gives the average

The basic TKPH calculationinvolves the following formula:

workingenergy that the tyre must withstandduring operations.

M =M + M

2 AL E

Equation 1 - Average Load on Tyre

Where:

M A = Average load on tyre.

ML = Tyre load on a loaded vehicle.

ME = Tyre load on an empty vehicle.

The average tyre load should becalculated for at least each axle onthe vehicle. If there is significantvariance across axles, thiscalculation should be performed foreach tyre position. The maximumvalue obtained from the calculationswill be used to determine the TKPHvalue.

The weight of equipment is bestdetermined from actual weighscaledata. If manufacturers data is used,allowances for extra equipment,partial water fill in tyres, mud onchassis, etc must be included.Weightscale data will also highlight ifoverloading, under loading oruneven loading occurs and if so to

what extent.The haul average speed iscalculated by Equation 2, givenbelow:

VT A

=L x N

Equation 2 - Average Speed

Where:

V A = Average haul speed (kph).

L = Haul length (kilometres).

N = Number of cycles per shift.T = Duration of shift (hours).

It should be noted that whenperforming the haul average speed

calculation, where there is more thanone haul route, the calculation mustbe performed so that the maximumaverage speed for the site isdetermined. The fastest haul route isnormally the longest.

Also, for the shift duration time,periods such as dwell time atshovels, unloading points, refuelling,meal breaks etc, are to be includedin the shift. Abnormal downtime isnot to be included in the shift timecalculation, for examplebreakdowns, stoppages etc.

As evident from the calculationmethod for the TKPH value, theactual TKPH value calculated is verygeneric. This causes severalproblems which have to beovercome. These include:

No allowance is made foroverloading of equipment.

As only the average speed of theequipment is used, there is thepotential to exceed this forlimited periods and henceexceed the tyres actual TKPHrating.

Actual TKPH of tyres in servicemay vary when compared torated TKPH through improvedroad design, maintenance andpressure maintenance.

The TKPH values quoted bymanufacturers assume certainstandards of pressuremaintenance, road condition,speeds and loads. If theseconditions are well controlledcompared to the assumed levels,actual tyre TKPH may actuallyincrease.

No allowance is made for loadvariations between the front and

rear of the tray. TKPH values supplied by tyre

manufacturers are only valid forcertain haul lengths, ambienttemperatures and speeds.

Even after a TKPH figure has beendetermined, it may have to bemodified to suit pit conditions further.Most TKPH values are quoted at astandard ambient of 38 C. Thereforeif the ambient temperature at yoursite is above or below thistemperature, the tyres TKPH rating

needs to be adjusted.It should be noted, that as mostearthmover tyres last approximatelya year, (depending on site

conditions), the maximumtemperature needs to be used todetermine the required TKPH. BothBridgestone and Michelin haveindividual formula for calculatingtemperature corrected TKPH.Goodyear do not require their TKPHvalues to be modified for ambienttemperatures.

An example of an actual TKPHcalculation is given in Appendix 1and 2.

Choosing The Actual TyreBased On TKPHNormally, the size of the tyre isalready determined by what wasfitted as original equipment.Depending on rim size, there are stillsome possibilities for tyre sizeadjustment, however this normallyrequires changes in rim widths or rimdiameters.

Therefore the starting point isnormally the tyre size that has beenoriginally fitted. Reference to theTyre and Rim Association StandardsManual will give load carryingcapacities for most tyre sizes andcarcass constructions.

Using the TKPH value calculated, achoice between the short listed bias-ply and radial tyres will have to be

made where this choice has notbeen made prior to this point.Normally the selection of bias-ply orradial tyres has been made prior tothis point for other reasons, such aswear life, cost etc.

Once the TKPH requirements havebeen determined for the site, actualmatching of tyres from vendors canbe undertaken. It is not within thescope of this article to specify howthis is performed, as the choice oftyres is dependant on manyvariables such as:

Tyre purchase cost

Warranty provisions

Service life

Brand performance

Availability / delivery

Consignment agreements

Rebates


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6 O T R A C O (International) Pty Ltd - Tyre Selection, Use and Operational Issu es to Maximi se Tyre Life Tyre MaintenanceTo maximise the performance oftyres utilised, correct operation andmaintenance is required. The mainfactors affecting tyre life are listedbelow.

Maintenance Pressure Maintenance

Pressure Setting Under Inflation Over Inflation

Road Maintenance Rocks in Road

Surface Over Watering Uneven Surfaces Rocks in Windrows

Tyre Maintenance Matching Dual Matching Asymmetrical Wear Rock Removal Run Out Parameters

Vehicle Maintenance Tyre Camber Alignment Toe In / Toe Out Brake Adjustments

Haul Road Design Curve Radius Road Width Road Surface Gradients Drainage Super Elevation

Operations Driving

Vehicle Speed Vehicle Positioning Cornering Speed Gear Changes Wheel Slip / Slide Avoidance of

Obstacles

Loading Load Position Load Weight Load Type

Loading Accuracy Face Condition Backing Trucks onto

Face / Rocks Scheduling

Balancing of TKPH Waiting Periods Break Periods Release for

Maintenance Tyre Selection

Construction Type TKPH Tread Wear Load Capacity

Traction

MaintenanceMaintenance activities include,pressure maintenance, roadmaintenance, tyre maintenance andvehicle maintenance.

Pressure MaintenancePressure Maintenance is the singlemost important contributor to tyrelife. The effects of incorrect pressuremaintenance can cause acceleratedwear along with other problems.Some of the typical problemsassociated with pressuremaintenance are:

Under Inflation Heat separation.

Uneven wear - excessive healand toe wear.

Internal ply separation.

Bead damage.

Increased fuel consumption.

Over Inflation Uneven wear (excessive centre

line wear).

Cuts.

Impact damage.

Figure 7 below, highlights the effectthat poor pressure maintenancestandards can have on the relativetyre life achieved in operation. Itshould be noted that the type ofoperation plays a major part in theactual wear rates, in conjunction with

pressure maintenance.There are many methods ofchecking earthmover tyre pressures.These range from simple visual

inspection to continuous monitoringsystems. A paper detailing threecommercially available systems isincluded as an Appendix to thisarticle.

It should be noted from Figure 7 that

under inflation not only affects tyrelife but also safety greater than overinflation.


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7 O T R A C O (International) Pty Ltd - Tyre Selection, Use and Operational Issu es to Maximi se Tyre Life The pressure setting for tyre is alsoimportant. An incorrect setting candramatically decrease tyre life, evenif pressure maintenance is good.Pressure settings can be initiallycalculated from the tyre load /inflation tables provided by tyremanufacturers. Allowances mayhave to be made based onoperational practices, such as partialwater fill, speeds or loading criteria.

Road MaintenanceRoad maintenance is usually notfactored into tyre life analysis.However road maintenance is vitallyimportant if extended tyre life is to beachieved.

Correct road maintenance requires acoordinated approach whichinvolves all personnel. All personnelshould have the ability to requestroad maintenance crews attend anarea of concern.

Road maintenance involves allaspects of maintaining the haulroads to a standard where tyre wearor damage is not accelerated. Thisincludes the removal of rocks layingon the road, rocks imbeded in theroad, grading of road surfaces to re-

level them, drainage channels andthe grooming of windrows andemergency stopping buffers.

Overwatering causes scouring anderosion of the roadbase, which canlead to overloading of individualtyres. Excessive watering can alsocause wheel spin and subsequent

removal of material leading togrooving of the roadbase withchannels which can increase tyreload.

It is important therefore that whenwatering haul roads, care should betaken to ensure that the road surfaceis not overwatered. This maynecessitate the use of pulsesprays. Pulse sprays are typicallywhere the water spray isalternatively on or off forapproximately 5 second periods.Other methods to reduceoverwatering include using the righthand sprays to wet the uphill side ofthe road whilst travelling downhill,not watering already wet roads, notwatering during rain periods andreduced water delivery rates.

Tyre MaintenanceTyre maintenance involves therectification of problems which if leftunchecked could lower tyre life. Thetimely rectification of these problemswill ensure that tyre life ismaximised.

There are many problems that tyrescan have during service. Theseproblems include asymmetrical wear

and rocks imbeded in the tread. Tocorrect for asymmetrical wear, thetyres are reverse mounted, whilstany embedded rocks should beremoved, as these tend to be drawninto the casing by the flexing of thetyre and can cause the inner liner tobe ruptured.

Incorrect matching of rear dual tyrescan increase loads in individual tyresdramatically. Matching of tyres isalso critical in loader and dozerapplications.

Most organisations have limits that atyre can be worn to and still be fittedto the steering positions of a truck. Ifthese criteria are too stringent, extratyres will have to be fitted to the frontposition and if the criteria are tooloose, this could lead to increasedrates of front tyre failures which mayhave safety consequences. Fronttyre failures also result in increaseddowntime due to tyre changesoccuring outside the workshopenvironment or having to transportthe vehicle back to the workshop.

Vehicle MaintenanceFrom a tyre perspective, correctvehicle maintenance includescamber adjustments, wheelalignment, toe in and toe out andbrake adjustment.

The correct alignment andadjustment of the wheel is critical toachieving long tyre life. If the tyre ismisaligned, the tyre will rotate at anangle to the desired direction oftravel. This causes slip and increasewear. Some mis-alignment isrequired for steering and stabilitypurposes, but this should be rigidlycontrolled.

Incorrect brake adjustment,especially dragging brakes cancause excessive heat loads on thetyre and premature failure. If the

Pressure Maintenance Standards - Effect on Tyre Li fe

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%80.0%

90.0%

100.0%

40%50%60%70%80%90%100%110%120%

Inflation Pressure - Percentage of Recommended B ase Pressure

% L

i f e

O b t a i n e

d

Very Demanding Operation Typical Operation Mild Operation

Figure 7 - Pressure Maintenance Relative to Tyre Life


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8 O T R A C O (International) Pty Ltd - Tyre Selection, Use and Operational Issu es to Maximi se Tyre Life heat levels are extreme there is thepossibility of a tyre fire of even a tyreexplosion. Both of these events havethe potential for serious injury.

Haulroad Design

The impact of haul road design isoften overlooked when comparingtyre performance, but this is one ofthe most critical aspects of achievinghigh tyre life. The United StatesDepartment of the Interior - Bureauof Mines prepared a book titled,Design of Surface Mine HaulageRoads - A Manual, authored byWalter Kaufman and James Ault in1977, which highlights the designrequirements for mine roadways.

This publication highlights safetyissues associated with mine road

design, along with methods ofintegrating vehicle dynamics andperformance into road design.

We will examine the following:

Horizontal and Vertical Alignment

Cross Fall Drainage Superelevation Curve Radii Road Construction Road Width

Horizontal and Vertical Al ignmentIn the interests of safety, whereeconomically feasible, all roadwaysshould be constructed to providesafe, efficient travel at normaloperating speeds. Provision foradequate sight of vehicles andobstacles should be paramount froma safety perspective. Adequate sightwill allow operators to avoidobstacles and also enable smootherbraking, thereby reducing wear andincreasing tyre life. Figure 8 gives agraphical representation of verticaland horizontal alignments tomaximise safe working.

The vertical alignment, grades,curve radii etc, is a function of theequipment being utilised.Consideration should be given to thebraking and haulage capabilities ofthe equipment (both current andfuture), to allow adequate stoppingdistances. Where equipment ishauling material up hill, then theequipments capacity and powerrequirements, along with brakecapacity must be considered.

Where gradients start, adequateblending of the transition betweenthe horizontal and grade areasneeds to be performed. Too often,steep grades begin with notransition, which causes theequipment to pitch and, ifoverloaded, deposit rocks andmaterial on the road surface.

These rocks cut the tyres surfaceand if large enough, cause impactdamage to the tyre.

Figure 7 - Road Alignment Criteria

At the lower end of grades, curves ifnecessary, should be of sufficientwidth relative to radius, to allow theequipment to easily traverse them.Here speed is the issue, as withcorrect super elevation, cornersshould not be a problem.

Horizontal alignment predominantlydeals with the safe operation ofequipment around curves at speed.Curves are regularly created withlittle regard to the operating speed ofthe equipment utilising them, thewidth of the equipment and stoppingdistances relative to visiondistances.

Cross FallCross fall on vertical sections is notnecessary, especially where pulsewatering can occur. If cross fall isused and is from the outside of theroad to the inside, water will tend todrain into the edge of any corner atthe bottom of the grade and causescouring and cutting of the surface.

Cross fall if excessive can causesteering difficulties and slip betweenthe tyres increasing wear. Where

cross fall is excessive the inner rearduals can be overloaded also.

DrainageDrainage is a major consideration,as during heavy rain large amountsof water can collect and run downthe grade, causing severe scouring.This scouring can cause overloadingof tyres or even impact damage.

Additional problems such asreduced traction and loss of controlcan also occur if drainage is notadequate. The combination of wettyres and wheel slip through loss oftraction dramatically increases thetyres wear rate.


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9 O T R A C O (International) Pty Ltd - Tyre Selection, Use and Operational Issu es to Maximi se Tyre Life SuperelevationIf curves are made which have verysmall radii and if there is no superelevation included, the tyres will tendto deflect and skid outwards,increasing loads and wear. Superelevation is a function of both thecurves radius and the equipmentsspeed. Table 5 gives super elevationrates (metres per metre) for a givencurve radius (metres) and equipmentspeed (kilometres per hour).There needs to be some practicallimits as to the amount of superelevation required. If a curve isdesigned for 45 kph, but in practiceequipment only achieves 20 kph,then the net effect is that the driverwill require extra effort to manoeuvrethe vehicle around the curve.

If the vehicle is moving slowly or hasto stop on a super elevated curve,the inner wheels will carry a higherpercentage of the load.Table 5 can also be used todetermine the correct entry speedsfor a given corner radius. Thesespeeds can then be posted toremind drivers of the correct speedprior to entering the curve.

As important, but often overlooked,is the relationship between superelevation and required run-out. Thesuper elevation runout is the length

of transitional road where theamount of super elevation changesfrom zero to the required, or frompositive super elevation to negative.

As the speed of vehicles at mostminesites is relatively slow, thepositioning of runout is not as criticalas other applications such ashighways or access roads. However,where cross fall is used on the roadsurface and it opposes superelevation, the necessary changes inroad surface slope should beachieved prior to the corner.

Curve RadiiSharp bends should be minimisedwhere possible. Figure 8 gives amethod of determining the roadwidth during a curve. From a tyre lifeperspective curves should be aslarge as possible. If this is notpossible speeds should be reducedto minimise the possibility ofaccidents.

Road ConstructionFundamental to the safe operation ofequipment is a stable road base.

Vehicle dynamics are severelyaffected by a roadbase which cannotadequately support the equipmentsweight. Productivity is also affectedby incorrect roadbase materials,

through tyre wear, rework (such asgrading and compacting), downtimedue to the disruptions that thiscreates and reduced operating

speeds of equipment required tonegotiate irregularities.

Too frequently, the economics ofroad construction is confined to theimmediate. Therefore, roads tend tobe built such that operations canbegin, rather than for the duration ofoperations. This usually means thatoperations will over time be subjectto delays through restrictions,rework, clearing, leveling andcleaning.Some common problems occurringwith road bases include:

Incorrect particle sizes

Low bearing strength

Flow under load

Scouring

Dust

Sinking

The geology and soil mechanicsassociated with road constructionwill not be discussed here.

Care must also be taken to selectthe most appropriate road surface.Figures for road adhesioncoefficients are given in various

publications, for example theCaterpillar performance handbook.The correct choice of road surfacematerial will provide not only higherlevels of adhesion, but also lowerrolling resistance and improved fueleconomy.

Figure 8 - Roadway Width during Curves

Radius ofCurve

Speed of Vehicle (kph)

(metr es) 10 15 20 25 30 35 40 45 5050 0.02 0.04 0.06 0.10 0.14 0.19 0.25 0.32 0.39

100 0.01 0.02 0.03 0.05 0.07 0.10 0.13 0.16 0.20

150 0.01 0.01 0.02 0.03 0.05 0.06 0.08 0.11 0.13

200 0.00 0.01 0.02 0.02 0.04 0.05 0.06 0.08 0.10

250 0.00 0.01 0.01 0.02 0.03 0.04 0.05 0.06 0.08

300 0.00 0.01 0.01 0.02 0.02 0.03 0.04 0.05 0.07

350 0.00 0.01 0.01 0.01 0.02 0.03 0.04 0.05 0.06

400 0.00 0.00 0.01 0.01 0.02 0.02 0.03 0.04 0.05

450 0.00 0.00 0.01 0.01 0.02 0.02 0.03 0.04 0.04

500 0.00 0.00 0.01 0.01 0.01 0.02 0.03 0.03 0.04

Table 5 - Recommended Super Elevation Rates (metres per metre)


10/18

10 O T R A C O (International) Pty Ltd - Tyre Selection, Use and Operational Issu es to Maximi se Tyre Life Road WidthRoad width is essential to the safeoperation of equipment.Earthmoving equipment varies insize dramatically between machinesof varying capacity. Therefore roadwidth needs to be set for the largestvehicle that would normally operateover a given route.

If there exists a large discrepancy inthe width between normal machineryand some plant, it may be moreappropriate to ensure that there issufficient width for the relocation ofthe equipment, which would have tobe moved under escort.

Table 6 and Figure 9 show relativeroad widths for varying numbers oflanes and equipment sizes.

Table 6 - Recommended LaneWidths (Straight Sections)

Only through proper road design canthe long term efficiency ofoperations, not only tyre wear, beguaranteed.

Operations have a high impact onthe overall tyre life. Normal tyre

failure modes, such as rockdamage, cuts, heat separations, etc,can to some degree be avoided bycorrect operational practices. Thesepractices will be discussed in thefollowing section of this article.

Operational Issues

Vehicle SpeedVehicle speed is also a critical factorin tyre life. Previously, only theactual operator could control vehiclespeed. However, with the advent of

modern computerised mine dispatchsystems, vehicle speed, andassociated tyre heating, can now bemonitored remotely. This monitoringis only a check system, it is notperfect, or 100% accurate.

Drivers should be made aware of thelimitations of the tyres that are fittedto the vehicles that they areoperating. Common tyre maximumspeed restrictions are given below inTable 7. This table is only a guideand each different tyre should bechecked for its maximum speed

rating.The average speed for a vehicleshould be less than the TKPH valueof the tyre divided by the averageload, ie: the workday or workshiftaverage speed.

Type of Vehicle MaximumSpeed

Earthmover 65 kph

Scraper 48 kph

Grader 40 kph

Loader & Dozer 10 kphTable 7 - Typical Vehicle SpeedLimitations

Excessive speed can result in manyproblems which can damage a tyre.These include:

Higher heat generation insidetyre

Heat damage

Heat separations

Rapid Braking

Chipping

Bead damage

Reduced tyre life

Sharp Cornering

Irregular wear

Excessive abrasion

Bead damage

Chipping through slip

Road Debris Collisions on Road

Cutting

Punctures

Cut / Burst

Vehicle speed can also cause otherproblems. When vehicles climb agrade when loaded, the drive tyres

can slip. Often this slip cannot beseen with the eye. The grade bywhich the vehicle has to ascenddirectly affects tyre wear. Figure 10shows the relationship betweengrade, vehicle speed and tyre life.The grade also affects the vehiclesmechanical systems such as brakes,drivelines and engines.

Figure 9 - Road Width Relative to Equipment Width(Horizontal Surfaces)

VehicleWidth

1lane

2lanes

3lanes

4lanes

(metres)

2.0 4 7.0 10 13.0

2.5 5 8.8 12.5 16.3

3.0 6 10.5 15 19.5

3.5 7 12.3 17.5 22.8

4.0 8 14.0 20 26.0

4.5 9 15.8 22.5 29.3

5.0 10 17.5 25 32.5

5.5 11 19.3 27.5 35.8

6.0 12 21.0 30 39.0

6.5 13 22.8 32.5 42.3

7.0 14 24.5 35 45.5

7.5 15 26.3 37.5 48.8

8.0 16 28.0 40 52.0

8.5 17 29.8 42.5 55.3

9.0 18 31.5 45 58.5

9.5 19 33.3 47.5 61.8

10.0 20 35.0 50 65.0

10.5 21 36.8 52.5 68.3

11.0 22 38.5 55 71.5

11.5 23 40.3 57.5 74.8

12.0 24 42.0 60 78.0

12.5 25 43.8 62.5 81.3

13.0 26 45.5 65 84.5

13.5 27 47.3 67.5 87.8

14.0 28 49.0 70 91.0

14.5 29 50.8 72.5 94.3

15.0 30 52.5 75 97.5

15.5 31 54.3 77.5 100.8

16.0 32 56.0 80 104.0


11/18


Figure 10 - Reduction in Tyre Life

with Road Grade and Speed

Figure 11 - Effects of Road Profileon Tyre Load

Vehicle Positioning

Figure 11 shows the impact thatpoor positioning of the vehicle canhave on the tyre load. This Figure

also highlights the need for goodroad maintenance along withadequate road width, to ensure thatthere is enough room to manoeuvre

around obstacles, or negotiatecurves etc at speed.

As can be seen from Figure 11,tyres can be severely overloadedsimply from falling into drainagechannels, mounting windrows, or

from simply being mis-matched. It isin these situations that side wallcuts, rock penetrations and impactbursts, along with internal damagecan readily occur.

Damage incurred throughoperational issues can be overcome,but requires regular informationaland training sessions with thoseconcerned, operators and drivers.Without their commitment,consequential damage will not bedramatically reduced.

Care must also be taken to ensurethat the design and maintenance ofroads are performed so that tyredamage is minimised.

As Figure 11 shows, tyreoverloading can occur even whenthe vehicle is correctly loaded,through road geometry or drivererrors. If however, the vehicle isalready overloaded, the problemsare increased dramatically.

Loading TechniquesIt is important that the loading

operation be carried out in a mannerto reduce tyre wear and damage.Figure 12 highlights the impact thatoverloading can have on tyre life,without any other factors included.

Care should be taken to ensure thatthe load is positioned properly,allowances are made for overburdenand ore densities, along withallowances for varying truck typesand capacities.

Figure 12 - Effects of Load on TyreLife

Other issues related to tyre wearand damage that occur whenloading, include backing onto theface, lack of face clean-up and

overfilling or missing the trucks traywhich results in stones falling underthe rear tyres.

Backing onto the face can causesevere over-loading on the rear tyresand increase the risk of rock cuts

and penetrations (Figures 13 & 14).This is exaggerated where largerocks are present. To remove thisproblem, regular face clean-upoperations should occur, along withaccurate loading and removingspilling, as this is the most commoncause of face debris. If accurateloading is carried out, eliminatingspillage, not only will face clean-upsbe less frequent, but there will beless likelihood of rocks falling underthe rear wheels.

Figure 13 - Overloading and Spillage

Figures 13 and 14 show actualloading operations. These practicesare treated as everyday practiceshowever they dramatically reducetyre life. Pit surveys and conditionreports can help to identify andcorrect practices such as these.

Figure 14 - Backing onto Loading Area

Figure 15 - Rocks around Face Area


12/18

12 O T R A C O (International) Pty Ltd - Tyre Selection, Use and Operational Issu es to Maximi se Tyre Life Figure 15, shows the accumulationof rocks, both at the face and in thearea around the face, that can occurfrom overloading. Not only do rocksfall from the tray during loading fromoverfilling, but they also fall from thetray when the vehicle begins tomove. This multiplies the work thatthe face clean-up crews have toundertake and dramaticallyincreases rock damage to tyres.

Figure 16 - Vehicle Parked on Rocks

Figure 16 shows a vehicle parked onrocks during a shift break. Careshould be taken to keep clean anyarea utilised by the equipment.Parking on rocks is very damaging

to the tyres, as the point loads thatoccur are present for a much greaterperiod of time, dramaticallyincreasing the probability of damageto the tyre.

Figure 17 - Uneven Loading ofVehicles

Figure 17 highlights uneven loadingin practice. This is a major concern,especially where road conditions arenot favourable. Care should betaken to always ensure that the loadis positioned correctly within the tray.

With the advent of new MineScheduling Systems, there is thepotential to increase truck utilisation,through more efficient dispatch /routing. This however has several

problems in relation to tyre life.

Unless an allowance is made for theincreased distance travelled andcorresponding increase in averagespeed, there exists a very highprobability that tyres will be operated

over their TKPH limits. Somecomputer systems attempt toaddress this issue through in-builttyre TKPH algorithms, but eventhese are too simplistic to accuratelypredict tyre TKPH. In severe casesthe error could be enough to eitherhave trucks stood down or tyresdamaged, depending on the triggerlevels set.

The new computerised MineScheduling Systems also increaseaverage speeds through a reductionin waiting times at both loaders andcrushers. This also may reduce tyrelife if not accounted for.

CONCLUSIONTyres usually account for 25% to

40% of a mining or quarryingoperations earthmoving costs. Assuch, there is a large scope for costreduction through improvements intyre utilisation.

Effective utilisation of tyres is not asimple task. The maximisation oftyre life requires a coordinated effortfrom proper selection through tomaintenance and operationalpractices.

The fundamental areas required toensure tyre life is maximised include;

Correct selection Correct pressure settings

Correct pressure maintenance

Correct tyre maintenance

Haul road design

Haul road maintenance

Correct loading methods

Correct load area housekeeping

Correct vehicle operations

Proper vehicle scheduling

Only if ALL of these areas areproperly addressed, will tyre lifeachieve the maximum possible.

Correct selection ensures that thetyre being utilised is the most costeffective solution for the combinationof vehicle, load and operatingconditions. The selection processinvolves many trade-offs and if anincorrect assessment is made, tyrelife can dramatically decrease.

Regular trials of tyres which may besuitable can also be carried out togain a quantitative assessment oftheir performance. This process canhowever take several years to

complete, during which tyreconstruction or compound changesmay make the results obsolete.

Pressure maintenance is the majorbuilding block upon which effectivetyre utilisation is founded. Without

correct pressure settings andpressure maintenance, tyre life willbe significantly reduced.

With an average earthmover tyrecosting in the vicinity of $10,000 oreven greater, the cost of a regularinspection program relative to thepotential losses is minimal.

Care should be taken to ensure thatemployees undertaking this processare properly trained to do so. Otracohas Australias only accredited tyreserviceman training program.

To maximise tyre life it is essentialthat haulroad design be adequatelyaddressed. Although the economicsof haulroad design are normallyconfined to the immediate, thelonger term ramifications candramatically exceed the short termbenefits.

The benefits of undertakingadequate haulroad design andconstruction include:

Reduced downtime

Reduced maintenance

Reduced consequential damage

Reduced tyre failures

Reduced tyre wear

Reduced machine maintenance

Improved operator comfort

Improved safety

Improved tyre life

Haul road design covers issues suchas curve radii, cross fall, horizontal

and vertical alignment, superelevation rates, drainage, camber,road widths, gradients, constructionmedium, base materials andsurfacing material. All of these areascan be optimised to ensure that themost suitable combination isachieved.

Haulroad maintenance is alsoessential to ensure effective tyreutilisation. Haul road maintenance isdependent on climatic variables,road construction techniques andoperational practices.

Tyre life will normally reflect the levelof haul road maintenance, if all othercriteria are equal. If the level of haulroad maintenance is high the tyre life


13/18

13 O T R A C O (International) Pty Ltd - Tyre Selection, Use and Operational Issu es to Maximi se Tyre Life will be relatively high, if haul roadmaintenance is low, tyre life will becorrespondingly low.

Operational issues can also have adramatic effect on tyre life. Some ofthe main operational issues which

impact on tyre life include loadingmethods, housekeeping of theloading area, vehicle operations andvehicle scheduling.

Loading methods predominantlyrevolve around the actual loadplacement on the truck and truckpositioning when loading. Careshould be taken to ensure thatspillage is reduced as spillage canfall under the tray making the tyreroll over it when leaving the loadarea. This causes the overloading ofthe tyre and increases the risk of a

rock impact damage or rock cut.If spillage occurs, or if rocks begin tofoul the load area, either the shoveloperator or a clean-up crew shouldclear the loading area prior tocontinuing. This reduces thelikelihood of tyres being parked onrocks, which can cause significanttyre damage. Good housekeeping inthe load area should not be seen aslost production time, if it is seen aspoor operational practice to causethis spillage in the first place,operator skills will improve.

Vehicle operations includes travelspeeds, cornering speeds, gearchanges, obstacle avoidance,braking methods, accelerationmethods and vehicle positioning. Allof these areas can impact on tyre lifeand have the scope to causepremature failures in the extreme.

Operators should be educated toensure that they are aware of theconsequences of poor operationalpractices. This education processhas proved to be very effective whencombined with accurate reporting inreducing the incidence of prematuretyre failures through operator error.

Proper vehicle scheduling is nowmuch more readily achieved throughmodern computerised mine dispatchsystems. However, the modelsutilised have some inconsistenciesin relation to TKPH calculations. Thealgorithms utilised however can stillprovide a useful first line of defenceagainst tyre damage.

It can be seen that effective tyreutilisation requires a coordinated

approach. To achieve the maximumlife for a tyre, ALL of the issuesraised must be addressed. Tyre lifedecreases with each criteria that is

not adequately controlled oraddressed.

The areas listed are not staticvariable and as such must becontinuously monitored to ensureadequate responses are made to

new developments. It is essentialthat periodic reviews of operationsare carried out to validateassumptions or confirm valuesutilised and therefore confirm theprocesses and tyres in use as beingstill optimal.

This process is ongoing. But with thecorrect type of tyre and effectiveoperational practices, effective tyrelife should be possible.

ACKNOWLEDGMENTS Historical and technical informationsupplied by the following companiesis gratefully acknowledged -Bridgestone Earthmover Tyres,Goodyear Australia Limited, Michelinand Rimtec. The author also wishesto thank Otraco and colleagues fortheir support and assistance.

REFERENCES1. Report to Minera Escondida Ltda

on tyre operation at Escondida,Otraco International, 1995

2. Developments in tyres forquarrying, A. T. Cutler, ProjectsManager, Otraco InternationalPty Ltd.

3. Proper tyre managementreduces tyre costs, D. M. Gordon& A. T. Cutler.

4. Design of surface mine haulageroads - A manual, United StatesDepartment of the Interior,Bureau of Mines InformationCircular, 1977, W. W. Kaufman& J. C. Ault.

5. Bridgestone Technical Data,Bridgestone Corporation,November 1994

6. Goodyear Off-the-road tyresengineering data, Goodyear

Australia Limited, 1994

7. Michelin Technical Data, small &large earthmover tyres, EditionNumber 15, Michelin Ltd.

8. The Tyre and Rim Association Australia - 1996 StandardsManual.

9. Caterpillar PerformanceHandbook, Edition 26, CaterpillarInc, 1995


14/18


APPENDIX 1 -EARTHMOVER TKPHCALCULATIONS

he follow calculations showthe TKPH determination for atypical haul truck, with the

following operating parameters,along with a brief overview of ahypothetical tyre selection process.

Based on the data above, the Average Load per Tyre can becalculated as follows,

Unloaded - Front

2 tyres, 47% of 61,793 kg equatesto:

Load =47% x 61,793 kg

2 TyresLoad = 14,521 kg / Tyre

Unloaded - Rear

4 Tyres, 53% of 61,793 kg equatesto:

Load =53% x 61,793 kg


Loaded - Front


Load =33% x 146,966 kg


Loaded - Rear


Load =67% x 146,966 kg


The average load per tyre can nowbe calculated.

Average Load Front Tyres:

M

M

A

A

=+

=

14 5 21 24 2 492

19385

, ,

, kg / tyre

Average Load Rear Tyres:

M

M

A

A

=

+

=

8 188 24 617

2

16 403

, ,

, kg / tyre

Therefore, the maximum averageload per tyre occurs on the fronttyres and corresponds to an averageload of 19,385 kg/tyre.

The site average speed must bedetermined from the two haul routesand cycle frequency informationgiven.

Therefore, for Haul Route 1;

V4.2 km x 30 cycles

8 Hours

15.75 kph

A1 =

=V A1

and, For Haul Route 2;

V6.8 km x 22 cycles

8 Hours

18.7 kph

A2 =

=V A2

Therefore, the highest averagespeed is achieved on haul route 2.Using the two maximum figures, thesite TKPH can be calculated asfollows:

TKPH = 19.385 Tonnes x 18.7 kph

TKPH = 363

This TKPH figure must becorrected for the sites highambient temperatures.

Using Bridgestones correctionfactor:

( )[ ]F(t C) =52

52 + 50 - 38 x 0.4

F(t C) = 0.92

o

o

This correction factor is multipliedwith the tyres rated TKPH to givethe tyres TKPH at 50 C.

To utilised the Michelin tyre data, theTKPH has to be corrected for twofactors. The first correction isperformed for ambient temperatureand the second correction isperformed for cycle length. As haulroute 2 is over 5 kilometres, the tyreTKPH factor has to be corrected.

Michelin quote correction factorcoefficients for varying route lengths.Using the data given for a routelength of 7 kilometres, the correctionfactor, K1 equals 1.06.

To correct for temperature, thefollowing formula must be used forMichelin data.

( )[ ]K2 =

V + 0.25 x TA - 38mVm

Where:

K2 = The correction factor.

T

Operating Weight 61,793 kg

Max. Gross Weight 146,966 kg

Weight Distribution(Empty)Front

Rear

47%

53%

Weight Distribution

(Loaded)Front

Rear

33%

67%

Standard Tyres 27.00R49

Standard Rim 49 x 19.50

Haul Route 1 Length(Return)

4.2 km

Haul Route 2 Length(Return)

6.8 km

Number of Cycles perShift (Route 1)

30

Number of Cycles perShift (Route 2)

22

Shift Duration 8 Hours

Site MaximumTemperature

50 C

Site MinimumTemperature

12 C

Road Condition Rocky

Dominant Failure Mode Rock cut /Impact

Current Tread Utilisation 53%


15/18

15 O T R A C O (International) Pty Ltd - Tyre Selection, Use and Operational Issu es to Maximi se Tyre Life Vm = The site average speed.

TA = Ambient site temperature.

Using this formula and the datagiven, we obtain:

( )[ ]K2 = 12.5 + 0.25 x 50 - 38

= 1.24

12 5

2

.

K

Therefore the corrected TKPH forthe given site conditions is:

TKPH = 363 x 1.06 x 1.24

TKPH = 477

Tyre SelectionTyre selection is normally performedindependently from the TKPHcalculation. The calculated TKPHvalues are used as a check todetermine if a particularconstruction,

Table 2 lists all availableBridgestone tyres in the 27.00x49size and their respective TKPHvalues, both rated and corrected.

Bridgestone

Tyre Type TKPH CorrectedTKPH

RLS 2A Bias 336 309.1

RLS 1A Bias 406 373.5

RLS 3A Bias 431 396.5

RLS 3AUH Bias 547 503.2

ELS 2A Bias 350 322.0 ELS 1A Bias 409 376.3

ELS 3A Bias 453 416.8

ELS 3AUH Bias 569 523.5 EL 2A Bias 423 389.2

EL 1A Bias 496 456.3

EL 3A Bias 555 510.6

EL 3AUH Bias 701 644.9

Table 2 - Bridgestone 27.00x49 BiasTyre TKPH Values

Tyre Type TKPH CorrectedTKPH

VKT/VFT 3A Radial 736 677.1



VEL / VRL 3A Radial 693 637.6



VMTS 3A Radial 652 599.8



VWTS / VRLS3A

Radial 611 562.1

VWTS / VRLS1A

Radial 530 487.6

VWTS / VRLS

2A

Radial 407 374.4

Table 3 - Bridgestone 27.00R49

Tyre TKPH Values

Tyres that are close to or under thecalculated TKPH rating are shown initalics.

Michelin

The TKPH values for the Michelin27.00x49 tyre size are given below.

Tyre TKPH

X VC 1090

X RB 763

X KB 698 X HD1A4 392

X HD1A 480

X HD1B4 567

X HD1B 654 X KD1A 392

X KD1B4 480

X KD1B 567Table 4 - Michelin 27.00R49 Tyre

TKPH Values

Goodyear

The TKPH values for the Goodyear27.00x49 bias tyres are given below.

Tyre Type TKPH

HRL-3B-4S Bias 380

HRL-4B-2S Bias 460 HRL-4B-4S Bias 328

HRL-4B-6S Bias 277

MRL-4D-4S Bias 277

SHY-7A-2S Bias 474Table 5 - Goodyear 27.00x49 Bias

Tyre TKPH Values

Goodyear radial tyre TKPH figuresare given below:

Tyre Type TKPH

RL3+ 2S Radial 628

RL3+ 4S Radial 474

RL-4-2S Radial 584

RL-4-4S Radial 445

RL-4J/4J-II-2S Radial 547

Rl-4J/4J-II-4S Radial 423 RL-4J/4J-II-6S Radial 328

Table 6 - Goodyear 27.00x49 TyreTKPH Values

DiscussionIt is not possible to accuratelyrecommend a tyre from those listed,as the tyre prices and stockavailability are unknown. This wouldplay a major part in any decisionprocess. However, based on the sitedata, a list of preferred option can beformulated.

It should be noted that the actualselection of tyres requires detailedknowledge of past and current tyreperformance, in both similar andvaried operations to determine tyresuitability prior to actually purchasingtyres and performing tests. Thisknowledge can save both time andresources by extrapolating knowndata to other sites, helping formshort lists of suitable tyres. Thisprocess is especially important whenpurchasing new equipment whichhas not been previously operated onsite.


16/18

16 O T R A C O (International) Pty Ltd - Tyre Selection, Use and Operational Issu es to Maximi se Tyre Life Based on the data given, thefollowing tyres would be short-listedfor trial:

BridgestoneBias-ply Tyres

ELS 1A - Standard construction,deep tread tyre withreasonable rock protection.

EL 2A - High rock protectionthrough cut resistantconstruction and materials,resistant to cutting, normaltread depth.

The corrected TKPH for these tyresclosely match the TKPH figurescalculated for the site conditions.The EL 2A should have a higherprobability of wearing out, through

the combination of strongerconstruction and standard treaddepth.

Radial Tyres

VRLS 2A - The tyres correctedTKPH is closely matched to theTKPH figures calculated for the siteconditions and the tyre has a cutresistant construction, with extradeep tread. With TKPH figuresbeing so closely matched, pressuremaintenance would have to beregularly carried out to preventdamage from improper inflation.

MichelinXHD1A - Good operating speed,

traction and reinforcementprotection.

XKD1B4 - Less traction and lowerspeed than XHD1A, butbetter reinforcement andprotection.

Both of these tyres have TKPHratings approximately equal to thesite corrected TKPH calculated.Through operational planning(varying haul trucks between the tworoutes and rigorous pressuremaintenance), these tyres shouldperform well in operation. Also, theTKPH ratings have a correctionfactor of 1.24 included for themaximum site temperature. As thesite minimum is lower, during thecooler months of the year, the tyresshould have a small margin of safetyincorporated. All of the tyresrecommended are deep treadtyres, giving 50% extra tread.

If operational and maintenancepractices are not able to beorganised to suit, then the followingtyres should be trialed:

XHD1B4 - Higher TKPH thanXHD1A, but lower cut andabrasion resistance.

XKD1B - High heat resistance forlong hauls, with the abilityto withstand minor

fluctuations in pressuremaintenance.

GoodyearRL-(4J/4J II)-4S-E4 - This tyre

combines a deep tread,standard construction tyrewith a cut resistantcomposition. The choicebetween the Rl-4J and theRL-4 tyres would be achoice between the wearand traction / ridecharacteristics of each tyre.

RL-4-4S - Also a deep tread,standard construction tyrewith a cut resistantcomposition.

There are only 2 Goodyear biastyres that would meet the TKPHrequirements and as both are heatresistant tyres, rather than cutresistant tyres, the optimum choiceis for radial tyres only.


17/18


18/18

18 O T R A C O (International) Pty Ltd - Tyre Selection, Use and Operational Issu es to Maximi se Tyre Life As both cycle lengths are under theminimums specified by Michelin,there are no restrictions placed ontyre selection by this criteria.

Based on the calculations performedand the data given, the Michelin tyre

recommended is the XLD D2A H -L5. This tyre has the advantage ofan extra deep tread (D2 / L5),combined with a construction highlyresistant to cutting, hacking andabrasion. The theoretical pressuresfor the front and rear tyres would be:

Front : 350 kPa (51 psi)

Rear : 200 kPa (29 psi)

Goodyear

Goodyear utilise a Work CapabilityFunction (WCB) to determine tyreselection for loader and dozerapplications. The WCF formula isgiven below:

M =M + M

2

=L x N

WCF = M x V

AvgEmpty Loaded

Trip Cycles

Avg Max

VTMa x Cycles

Where:

M Avg = Average tyre load.MEmpty = Empty tyre load.

MLoaded = Loaded tyre load.

VMax = Maximum average speed perhour.

LTrip = round trip distance.

NCycles = Number of cycles perperiod.

TCycles = Length of period (hours).

Using the data given for theoperation of the loader, we cancompute the WCF:

Take maximum load to be the

combination of the operating weightand the static tipping load (straight)distributed over the front tyres only,with the empty load being thevehicles operating weight distributedover all four tyres.

Therefore:

M =

47,906 kg2 tyres

+29,019 kg

4 tyres2

M = 15,604 kg / tyre

Avg

Avg

and

VMax = 8.4 kph

Therefore:

WCF = 15,604 kg/tyre x 8.4 kphWCF = 131 (metric WCF)

Using the Goodyear tyre informationfor the 29.5x25 tyre size, thefollowing tyres are available whichhave a WCF equal to or greater than131:

Tyre Type WCF

GP-2B-4S Radial 226

GP-2B-6S Radial 190

RL-2F-4S Radial 168

RL-2F-6S Radial 161

Table 10 - Goodyear 29.5R25 WCF

Of the tyres available, the followingwould be the recommended choice:

GP-2B-6S-L3 Radial.

This choice is made as this tyre canbe ordered in a L3 (Rock)construction, with a 6S materialspecification, ultra abrasion resistant

material and the WCF factor is highenough to allow a moderate marginof safety.

The theoretical pressures for thefront and rear tyres would be:



BridgestoneBridgestone utilise a TKPHcalculation to determine the correcttyre to be utilised.

For the loader, the loaded weightcorresponds to a full bucket(assume 75% rock and 25% earthwith a density of 2000 kg/m 3). Thisgives a loaded weight of 39,419 kg.

Using this figure:

M =39,419 kg + 29,019 kg

2

M = 34,219 kg

A

A

The average speed of the loader is8.4 kph. Therefore, assuming thatthe average load acts over the twofront tyres only:

TKPH =34,219 kg

2 x 8.4 kph

TKPH = 144

Using the Bridgestone productcatalogue, there are two tyres thathave a TKPH rating over 144, theseare:

FG-2A

VALS H

The FG-2A tyre would need to be a28 ply or higher tyre to cope with theloads placed upon it. Using the 28ply tyre, the theoretical tyrepressures would be:

Front : 400 kPa (58 psi)Rear : 225 kPa (33 psi)

The VALS H tyre would have thefollowing theoretical tyre pressures:



Type of Tyre Maximum Length of CyclePermissible (Round Trip)

Average Numberof Kilometres

Allowed in OneHour

XHA, XRA, XRDNA 1,800 m 16 km

XR D1A, XLD D1A 1,800 m 14 km

XR D2A, XLD D2A,

X Mine D1

1,500 m 10 km

X Mine D2, XSM D2 1,200 m 6 km

Table 9 - Michelin Tyre Selection Guidelines

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