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Fuel Saving Workshop: Selecting The Right Rubber

Once all the engine designers, transmission boffins and production engineers have clocked off and disappeared to the pub, one small hurdle has to be crossed before tractors can turn diesel into acres worked. Fire up the engine, go to move off and power floods down to the axle ends — but that’s where it will stay without tires to take it to the ground. And, according to Michelin, that final short hop is where money can be wasted.

The humble tire is the link between axles and the land. Only today’s tires are not so humble: like the tractors and implements that ride on them, they have blossomed technically. So much so that the only true way to maximize machine efficiency is to understand what modern rubber can do for you, pick the products that best suit your equipment (ideally at machine buying time), then run the new tires at the correct pressure(s). And that logic applies as much to old kit (tractors) as it does to new.

But are there really savings to be made? All major tire makers agree that there are. Michelin sponsors the Agricultural Contractor’s Panel (MACP): made up of five past winners of the Contractor of the Year Award, its aim is to encourage good practice by example. Which explains why 80-odd contractors, farmers and industry specialists came to be standing in a field close by Claas’s U.K. headquarters at Sax-ham, Suffolk, witnessing a range of tires busily engaged in the act of saving hard-earned cash.

Three demos were aimed at saving fuel and/or reducing soil damage. Even in dry, dusty conditions not best suited to revealing the differences between types, the results turned out to be interesting and pretty clear-cut. So, here’s what happened.

Can fuel be saved in heavy draught work by thoughtful tire choice? An instrumented Claas Axion 820 pulled a 7f Lemken semi-mounted plough, first on Michelin’s conventional AgriBibs then on its high-tech XeoBibs: for info on tire types and differences, see “Tire round-up” later in this article. In both cases, pressures were set to suit the load and the job. Draught load on the tractor in work was monitored by Scarlett research and held at 5.5 tonnes. Forward speed, wheelslip and fuel use were measured.

DRIVE TIRES — CONVENTIONAL VS LOW-PRESSURE ( “ULTRAFLEX”) TECHNOLOGY

Test Comment: Thanks to their much greater internal volume, the wider XeoBibs can run at 50 per cent lower pressures while supporting the same load. Their 42 per cent bigger footprint spreads weight over more soil so ground pressure comes down and traction goes up — wheelslip is reduced by almost 35 per cent. Less per cent slip means 10 per cent more drawbar power, 9 per cent less fuel use and 10 per cent faster work. Overall fuel efficiency rose by 6.7 per cent.

TRAILER TIRES — CONVENTIONAL VS FLOTATION

Many farms run their trailers on super singles. These are commercial vehicle tires with steel-braced sidewalls, designed to give great carcass longevity but requiring very high inflation pressures to support load. What would be the effect on fuel consumption of switching to more flexible, purpose-designed trailer tires, able to handle the same loads and speeds but at lower pressures? To see, identical 18 tonne tandem-axle trailers, carrying 14 tonne payloads, were pulled over cultivated land by a 155 horsepower Claas Arion 640. One trailer was shod with super singles, the other with Michelin’s CargoXBib flotation tires.

For each of the set-ups, Scarlett research monitored the draught force required to pull the trailer, the combination’s forward speed, tractor wheelslip and drawbar power demanded.

This 7f Lemken was pulled by the same Axion 820 on two sets of drive tires — conventional and XeoBibs. An instrumented linkage measured draught forces (purple frame, inset). Separate ground speed radar provided speed info, allowing drawbar power calculation.

Then to effectively highlight the effects on ground compaction, Wright resolutions (an independent soil specialist company) wielded a penetrometer in the trafficked areas.

Test Comment: in the sizes used, the CargoXBib has a footprint more than twice as big as the equivalent super single. The effect of spreading the trailer’s load is immediate: its rolling resistance drops and wheelings are much shallower. Draught load on the tractor is halved, drawbar power requirement is almost halved, wheelslip falls by 43 per cent and forward speed goes up by 16.7 per cent. The calculated energy requirement is around 45 per cent less — which means a substantial fuel saving if the driver isn’t tempted to exploit the situation through even faster travel. Soil compaction was strikingly different between the tire types. Penetrometer readings in the ruts left by super singles suggested root growth would be blocked without further cultivation, and compaction extended deep below the surface.

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Set-Up: Conventional Tires Rear: Agribib 520/85 R42, 25 Psi

Set-Up: Ultraflex Tires Rear: Xeobib Vf710/60 R42, 12.5 Psi

Front: AgriBib 420/85 r30, 20 psi

Front: XeoBib VF600/60 r30, 9 psi

———

Set-Up: Super Singles Size: 385/65 R22.5, Inflation Pressure 90 Psi Set-Up: Flotation Tires Size: 560/60 R22.5, Inflation Pressure 32 Psi

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14

TIRE TYPE

CHANGE PER CENT 10.3

12.76

Forward speed (k. p. h) Conventional 6.82 Ultraflex 7.52

Drawbar power(kW)

Tire footprint (cm)

*Combines drawbar power with fuel consumption kilowatt (= 1.341 horsepower) litres per hectare

**kilowatt hours per litre

104.2

3024

9.22

114.8

4312

-34.1

10.2

42.6

Wheelslip (per cent)

Fuel use (l/ha)

Efficiency* (kWh/l**)

3.42

11.61

3.65

-9

6.7

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22 6

RESULTS

TIRE TYPE CONVENTIONAL FLOATATION

CHANGE PER CENT

Draught load (kN)

Forward speed (k. p.h.)

Wheelslip (per cent)

Power required

Tire footprint (cm)

Average rut depth (mm)

Energy requirement

*At 7 k.p.h. Drawbar power required (kW)

14

37

1520

240

11

7

8

20

3300

165

Calculated value

-50

16.7

-43

-46

117

-31.2

-45

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Tire Round Up —Products Used In TheMACP Demo Were:

Agribib: 85-Series Radial Drive Tire For 60 To 160 Hp Tractors. Xeobib: Low-Profile 60-Series Radial Drive Tire For 80 To 200 Horsepower Tractors. Wider Than Agribibs And With Lower Side-Walls, So Enclose More Air And Have A Bigger Footprint. Ultraflex Technology Lets The Tire Run Cooler By Increasing The Tire Wall Flexion Zone Length, Reinforcing The Shoulder Areas And Adding Decoupling Rubbers To Reduce Heat Build Up. Xeobibs Are Designed To Operate At Up To 65 Km/H. (40 M.P.H.) At Pressures Up To A Max Of 1 Bar (15 Psi). Compared To A Conventional Or Low Profile Radial, The Equivalent Xeobib Can Carry Up To 40 Per Cent More Load At The Same Pressure, Regardless Of Speed. Claimed Pluses Include Reduced Wheelslip, The Ability To Replace Dual Wheels, No Need To Adjust Pressure Between The Field And The Road And Better Driver Comfort Cargoxbib: 65-Ser Ies Tra-Iler Tires With Steel Bracing Under The Tread. More Flexible Casing And A Bigger Footprint Than On Equivalent Super Singles; Carries The Same Load At Much Lower Pressure.

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