The tyre designer’s job, it seems, is never done. As tractors continue to gain power and weight to meet farmer demand for greater performance, new tyre designs are needed to provide an effective interface between power unit and the soil.
Alliance 363 Agriflex
Row-crop tyres in the Alliance range already come in 55 sizes, including the 350 Row Crop as one of the first tall and narrow tyres to be rated for use at 65kph, but options have been further increased by the new 363 Agriflex, which is designated “IF” to indicate the Improved Flexion characteristics of the sidewall.
“IF” in the size marking indicates a tyre with greater sidewall flexibility for a given load and inflation pressure than a regular design, so the tyre can place a larger footprint on the ground than a non-IF rated tyre of the same size.
An unusual feature of the 363 Agriflex design is its tread pattern; instead of the usual continuous lugs, the directional pattern is formed from a number of blocks.
Alliance says this produces a very “grippy” tread with good traction in soft conditions but also a larger proportion of rubber contact area, resulting in a long service life and lower rolling resistance during road travel.
The steel reinforced carcass has a “D” speed rating, which means it is approved for up to 65kph.
Compared with a standard tyre of the same size, the 363 Agriflex can run at a 20% lower inflation pressure for a given load or carry 20% more for the same inflation pressure.
At present, the newcomer is available in a single size – IF 320/90R46.
Four new sizes added to the Michelin AxioBib range cater for the highest horsepower conventional tractors.
Two 38in front sizes are matched with a pair of 46in tyres for the rear – IF 750/75R46 and IF 900/65R46. Fendt has adopted the larger size as standard equipment on 420-500hp versions of the 1000 Vario series tractors.
Like other tyres constructed using Michelin’s Ultraflex technology, the biggest AxioBib sizes have a strong, but supple sidewall that produces a large tread contact patch.
A novel additional feature is that the tyres are micro-chipped, enabling operators to access a personalised digital support service.
After registering by smartphone, operators can arrange a technical visit to have their tractor and implements weighed for accurate inflation pressure calculation and get tyre management advice relating to their particular set-up online.
The ability to mount “VF” rated traction tyres on standard rims in place of a less capable tyre is a feature of the Bridgestone VT-Tractor design, the premium line that complements the Firestone agricultural tyre range.
The all-new design caters for tractors of around 150hp and upwards and is available in several 28in to 38in rim sizes in various low-profile configurations.
It meets the performance standard defined for tyres to carry the “Very high Flexion”, which means it combines the strength and load capacity to carry 40% more load than a reference tyre at the same pressure and with a high degree of sidewall flexibility.
Like other “VF” rated tyres, the VT-Tractor can be operated at 65kph (as long as the relevant load limits are observed) and avoid the usual compromises between road travel and field work pressures by handling both at inflations down to 1 bar or less.
Normally, “VF” tyres have to be fitted to a wider rim than their “conventional” counterparts, but Bridgestone says half of the 22 sizes envisaged can be used on a standard rim.
Outwardly, the new tyre is distinguished from its Firestone forebears by a longer inner end to the lug, which projects further into the centreline of the tread, a pointed lug nose to encourage penetration and a larger leading edge surface to the lug to enhance traction.
A new design of lug, with a ledge built into the leading face, has produced significant improvements in traction on soil, say Trelleborg engineers of their ProgressiveTraction technology.
The so-called ‘double lug’ is reinforced at its base and so more resistant to bending back under torque load.
The reinforcing block, which has a sharp edge and flat top rather than blending smoothly into the main structure, increases the soil contact area by 5%, while also providing two “bites” at the soil. The structure also distributes torque forces more evenly across the lug.
Early comparative tests showed more than 10% extra traction versus control tyres and with further testing now under the R&D team’s belt, Trelleborg confidently claims as much as 18% improved traction over the industry average. In one test, the traction gain meant it took 3% less time to plough 200ha.
The Trelleborg TM700 ProgressiveTraction is the first tyre range to feature the double lug. Sizes from 420/70R28 to 620/70R42 are the first sizes available.