Track systems have become increasingly popular for combines to minimise soil compaction. But tyre manufacturers have been hard at work developing new designs that give similar benefits. Peter Hill reports.

Street furniture is the main problem with combine operators with width restrictors designed to limit the speed of traffic entering and exiting some of our towns and villages make life difficult when moving big combines by road from one block of land to another.

It is partly for that reason that a large proportion of Claas Lexion combines are ordered on Terra Tracs – it keeps overall width within manageable proportions while spreading the weight of the machine in the field.

Tyre manufacturers keen to keep supplying products for heavy harvest machinery aim to keep a foothold in this market by developing more sophisticated tyres. While still being capable of supporting the considerable weight of a combine, they retain practical section widths, but reduce compaction by using greater carcass flexibility to plant a longer than usual contact patch.

Michelin CerexBib first put in an appearance last year when it became an exclusive fitment on Claas combines – the two manufacturers collaborated on the development of the new tyre.

It is now available as a replacement tyre for other combines with sizes that include the IF 680/85 R32, VF 520/80 R26, IF 800/70 R32 and VF 620/70 R26. A further six sizes are expected by the end of this year.

The letters preceding the metric sizing give a clue to the tyre’s performance characteristics: VF refers to Very high Flexion; IF to Improved Flexion. These markings first appeared on Michelin’s XeoBib and AxioBib tractor tyres to highlight the patented Ultraflex technology that gives them exceptional sidewall flexibility, but sufficient strength and integrity to carry high loads at road speeds using inflation pressures previously reserved for the field.

Goodyear’s new combine tyre also carries the “IF” prefix to reflect its highly flexible carcass design. Currently available in three sizes (IF 800/75 R32, IF 800/70 R32 and IF 900/60 R32), the Optitrac H+ is designed to operate with greater sidewall deflection than usual to plant a larger footprint, but otherwise has the same design features as other designs in the Optitrac range, such as the asymmetric lug shape.

“Extensive testing and evaluation by combine manufacturers has shown that the entire harvesting operation can be carried out using one constant inflation pressure for both road and field work,” says Phil Stanton of Goodyear’s UK agriculture team. “The lower inflation pressure and higher load capacity of the Optitrac H+ tyre provides an increase in footprint area that improves traction and reduces the vehicle’s impact on the soil while reducing rolling resistance and improving fuel consumption.”

Compared with an 800/70 R32 Optitrac DT830, the equivalent IF 800/70 R32 H+ carrying the same 8,500kg load can be operated at 0.6 bar lower inflation pressure. Looked at another way, it can carry a maximum load of 13,174kg at 2.4 bar when a DT830 is limited to 10,710kg at a higher 3 bar inflation pressure.

A trial commissioned by Michelin to compare the impact of using standard and CerexBib tyres found significant differences in soil compaction.

Conducted by former Simba International technical director Philip Wright, and now an independent consultant, the trial included Michelin’s MegaXbib and MachXbib tyres, plus standard fitments from two other manufacturers. Inflation pressures were set according to each manufacturer’s recommendations for the relevant axle loadings, which included road configuration and in-field operating configuration with the grain tank 80% full.

In field configuration, the combine put a load of 10,740kg on the nearside front tyre, 8,800kg on the offside, or 19,540kg in total. The rear tyres carried 4,010kg on the nearside, 4,060kg on the offside, for a total of 8,070kg across the axle and 27,610kg in total.

After two runs with each tyre configuration across soil that had been loosened and re-compacted to provide consistent results, soil penetration measurements showed significantly lower compaction levels from the CerexBib: a mean of 1,099kPa compared with 1,425kPa for a MegaXbib (front) and MachXbib (rear) combination, and 1,506kPa and 1,603kP for the “other brand” tyres.

“It is clear that for depths to 25cm, the compacting effect of the Ultraflex technology tyres is significantly lower than the conventional tyres, which all gave broadly similar effects,” says Mr Wright. “Plant root growth and yield potential would be less adversely affected by using CerexBib tyres.”

Michelin commercial director Rob Beddis emphasises that the CerexBib is unique for being 15% narrower than any conventional harvester tyre with the same load index and diameter and the only commercially available harvester tyre that can operate at less than 2 bar (29psi) pressure – around 30% less than conventional tyres.

“The larger contact patch and lower ground pressure not only reduce rut depth and soil compaction, but they increase traction on wet and dry soil to also contribute improved fuel efficiency,” he adds. “The extremely flexible sidewalls also considerably improve ride comfort, with vibration and noise also reduced.”

Track developments

Having toyed with track assemblies from specialist manufacturers in previous years, John Deere has produced its own system for the new S-Series combines.

Available on level land combines only (HillMaster slope compensating versions must remain on wheels and tyres), the track system wraps a 660mm wide rubber traction belt around an upper drive wheel and large front and rear idler wheels. Three rollers between the idlers keep the belt firmly in contact with the surface.

“The hydraulic suspension is designed to provide a smooth ride for the combine and operator, both on the road and when working in the field,” notes product manager Mark Smith.

Growers facing extreme harvesting conditions with their Claas Lexion Terra Trac combines can get more traction and increased flotation by fitting the undercarriage with one of two wider traction belts.

Built by Canadian manufacturer Camoplast to Claas specification, the largest of the two increases ground contact area by 40%, giving Lexion 670 straw walker combine and 750, 760 and range-leading 770 rotary separation models greater ability to cope with challenging late-season conditions.

“We’re not actively promoting the new traction belt sizes here because most users will be content with the standard width belt,” says product manager Tom Pine of Claas UK. “They are intended mainly for countries where combines are harvesting grain maize in wet conditions; but if we had a customer in, say, Scotland working on steep hills and wanted the wider belts, we could supply them.”

At present, the Terra Trac undercarriage is fitted with a 635mm wide Camoplast belt with a ground contact area of 2.32sq m. Factory product specialist Jens Broer notes that with the 735mm belt available exclusively on the Lexion 750 narrow-frame rotary separation combine, this increases by 15.5% increase.

“Where mobility is not a great issue and the operator wants maximum flotation to minimise ground compaction, then there is an 890mm option for the 750 that is also be available for the 770.”